If you’re like me (and apparently many other people), when you start using (no pun intended) WCF by creating a client channel, it’s only a matter of time before you realize that you’re probably doing it wrong. 

Problem number one is that if you don’t explicitly close the connection, it’s only a matter of time before the connection starts faulting.  So you say to yourself, “Aha!  I need to close the damn connection.  And since I’m a good .Net programmer, I see the IChannelListener interface extends the IDisposable interface so I can just wrap my call in a ‘using’ statement which will explicitly clean up all my resources no matter what happens during the method execution.”

And then an exception happens.  Even though you wrap your call in the using statement, you see this weird exception about the channel being in the faulted state (or something like that).  Wait – I wrapped my call in the using statement.  This should work!  So you fire up GoogleBing and quickly learn the WCF team made the decision to implement IDisposable wrong uniquely. 

In order to get a WCF client to work as expected, you need to workaround the decision made by the WCF team and wrap all your WCF calls in blocks similar to this one:

          
  1: var channelFactory = new ChannelFactory(binding,
endpointAddress); 
          
  2: 

          
  3: var proxy = channelFactory.CreateChannel<ICustomerService>();

          
  4: IClientChannel clientChannel = (IClientChannel)proxy;

          
  5: bool isSuccessful
= false; 
          
  6: try
          
  7: {

          
  8:   proxy.AddCustomer(customer);

          
  9:   clientChannel.Close();

          
 10:   isSuccessful = true; 
          
 11: }

          
 12: finally
          
 13: {

          
 14:   if (
!isSuccessful ) 
          
 15:   {

          
 16:     clientChannel.Abort();

          
 17:   }

          
 18: }
        

As you can see here, you must explicitly call Close() on the client channel unless an Exception is thrown, in which case you need to call the Abort() method.

This code doesn’t just emit a code smell of violating the DRY principle, it absolutely reeks of it.  Steve Smith (and others) have come up with extension/utility methods aimed at simplifying the call and removing the repetitive boiler plate code from the above example.  Inspired by these solutions, I’d thought I’d throw out my own answer to this problem:

          
  1: publicclass WcfClient<TInterface> 
          
  2: {

          
  3:   public WcfClient(Uri
uri) : this(uri, new NetTcpBinding(SecurityMode.None)) 
          
  4:   {

          
  5:     Uri = uri;

          
  6:   }

          
  7:   

          
  8:   public WcfClient(Uri
uri, Binding binding) 
          
  9:   {

          
 10:     this.Uri
= uri; 
          
 11:     this.Binding
= binding; 
          
 12:   }

          
 13:   

          
 14:   public Uri
Uri 
          
 15:   {

          
 16:     get; 
          
 17:     privateset; 
          
 18:   }

          
 19:   

          
 20:   public Binding
Binding 
          
 21:   {

          
 22:     get
          
 23:     privateset; 
          
 24:   }

          
 25: 

          
 26:   publicvoid Using(Action<TInterface>
serviceAction) 
          
 27:   {

          
 28:     TInterface proxy = CreateChannelFactory().CreateChannel();

          
 29:     IClientChannel clientChannel = (IClientChannel)proxy;

          
 30:     bool isSuccessful
= false; 
          
 31:     try
          
 32:     {

          
 33:       serviceAction(proxy);

          
 34:       clientChannel.Close();

          
 35:       isSuccessful = true; 
          
 36:     }

          
 37:     finally
          
 38:     {

          
 39:       if (
!isSuccessful ) 
          
 40:       {

          
 41:         clientChannel.Abort();

          
 42:       }

          
 43:     }

          
 44:   }

          
 45: 

          
 46:   public TResult
Using<TResult>(Func<TInterface, TResult> serviceAction) 
          
 47:   {

          
 48:     TResult result;

          
 49:     TInterface proxy = CreateChannelFactory().CreateChannel();

          
 50:     IClientChannel clientChannel = (IClientChannel)proxy;

          
 51:     bool isSuccessful
= false; 
          
 52:     try
          
 53:     {

          
 54:       result = serviceAction(proxy);

          
 55:       clientChannel.Close();

          
 56:       isSuccessful = true; 
          
 57:     }

          
 58:     finally
          
 59:     {

          
 60:       if (
!isSuccessful ) 
          
 61:       {

          
 62:         clientChannel.Abort();

          
 63:       }

          
 64:     }

          
 65: 

          
 66:     return result; 
          
 67:   }

          
 68:   

          
 69:   private ChannelFactory
CreateChannelFactory() 

          
 70:   {

          
 71:     var endpoint = new EndpointAddress(Uri); 
          
 72:     returnnew ChannelFactory
(Binding, endpoint); 

          
 73:   }

          
 74: }
        

The two Using() methods offer an overloaded way to invoke a method on the service proxy.  In the first version, you can invoke an Action call which doesn’t expect a returned value.  In the second version, the TResult generic type determines the type of value expected from the invocation of the proxy object.  The return value will flow through from the proxy call execution to the caller.  Think of these two methods as being akin to the differences between a Sub or a Function in VB (my God, did I just admit to knowing VB?!?!?!).

The WcfClient code is responsible for creating the client proxy and returns the proxy back to the calling code.  As the caller, here is how you would execute the methods:

          
  1: string wcfUri
= ConfigurationManager.AppSettings["wcfUri"]; 
          
  2: 

          
  3: var wcfClient = new WcfClient<ICustomerService>(wcfUri); 
          
  4: 

          
  5: wcfClient.Using(proxy => proxy.AddCustomer(new Customer())); 
          
  6: 

          
  7: //
...
          
  8: 

          
  9: Customer[] customers = wcfClient.Using(proxy => proxy.GetCustomers());
        

The nice thing about this solution is that we take care of the exception handling and correctly clean up our resources in one place, and that logic is completely shielded from the calling code.  Plus, we can account for situations where a return value is expected versus when one is not.

In my last post, I discussed how to use DataSet objects with Miado.  In this post, I will tackle a common problem – building dynamic queries.

ISqlQuery Interface

I have created an ISqlQuery interface that can be used to run dynamic queries.  The interface is quite simple.  It exposes three properties – IsBuilt, Parameters, and Sql – and one method – Build(). 

          
  1: public
interface ISqlQuery 
          
  2: {

          
  3:     bool IsBuilt
{ get; } 
          
  4:     string Sql
{ get; } 
          
  5:     IDictionary<string, object>
Parameters { get; } 
          
  6:     void Build(); 
          
  7: }    
        

The idea behind this design is for the Sql property represents the SQL that will eventually be run against the database.  It can be built up dynamically based on the filtering that is applied to the object.  The same goes for the Parameters property.  It represents the DB parameters that will be bound to the Sql statement.  Parameters can be added to this property in the same way they are added to a IDbStatement.  By doing so, you can still safely use parameterized queries (as opposed to dynamically substituting the variables straight in the SQL string – i.e. String.Format(“and Name=’{0}’”, name), which exposes a risk for SQL Injection attacks).

The Build() method should be the place where you put your logic to dynamically create the SQL and populate the parameters. 

          
  1: public
class CustomerQueryByCityAndState : ISqlQuery 
          
  2: {

          
  3:     privateconststring SELECT_CUSTOMERS_BASE_SQL
= 
          
  4:         "select
CustomerID, Name, Address1, Address2, City, County, " + 
          
  5:         "StateCode,
ZipCode " + 
          
  6:         "from
Customers " + 
          
  7:         "where
1=1 "; // etc...
          
  8: 

          
  9:     public CustomerQueryByCityAndState(string city, string state) 
          
 10:     {

          
 11:         City = city;

          
 12:         State = state;

          
 13:         Parameters = new Dictionary<string, object>(); 
          
 14:     }

          
 15: 

          
 16:     publicstring City
{ get; privateset;
} 
          
 17:     publicstring State
{ get; privateset;
} 
          
 18: 

          
 19:     publicbool IsBuilt
{ get; privateset;
} 
          
 20:     publicstring Sql
{ get; privateset;
} 
          
 21:     public IDictionary<string, object>
Parameters { get; privateset;
} 
          
 22: 

          
 23:     publicvoid Build() 
          
 24:     {

          
 25:         var sb = new StringBuilder(); 
          
 26:         sb.Append(SELECT_CUSTOMERS_BASE_SQL);

          
 27: 

          
 28:         //
add City
          
 29:         sb.Append(" and
City = @City "); 
          
 30:         Parameters.Add("City",
City); 
          
 31: 

          
 32:         //
add State
          
 33:         sb.Append(" and
StateCode = @State "); 
          
 34:         Parameters.Add("State",
State); 
          
 35: 

          
 36:         //
Populate the SQL
          
 37:         Sql = sb.ToString();

          
 38:     

          
 39:         //
info
          
 40:         IsBuilt = true; 
          
 41:     }

          
 42: }
        

Though it’s not actually being for used anything now, the last step of the Build() method should flip the IsBuilt property to True.  This is purely for information purposes at this point, but it could be informative to the calling class.

SqlQuery Abstract Class

To simplify things, I have created a base class you can use that implements the ISqlQuery interface.  It manages the Sql and the Parameters, and will automatically flip the IsBuilt property when the Build() method is called.  The only thing a derived class must do is implement the DoBuild() method, which is a template method to actual perform the logic that was previously implemented in Build().  It should contain the logic of dynamically creating the SQL and Parameters.

          
  1: protectedabstractvoid DoBuild(); 
          
  2: 

          
  3: publicvirtualvoid Build() 
          
  4: {

          
  5:     DoBuild();

          
  6:     IsBuilt = true; 
          
  7: }
        

So the previous example above becomes much simpler…

          
  1: public
class CustomerQueryByCityAndState : SqlQuery 
          
  2: {

          
  3:     privateconststring SELECT_CUSTOMERS_BASE_SQL
= ... 
          
  4: 

          
  5:     public CustomerQueryByCityAndState(string city, string state) 
          
  6:     {

          
  7:        City = city;  

          
  8:        State = state;

          
  9:     }

          
 10: 

          
 11:     publicstring City
{ get; privateset;
} 
          
 12:     publicstring State
{ get; privateset;
} 
          
 13: 

          
 14:     publicoverridevoid DoBuild() 
          
 15:     {

          
 16:         var sb = new StringBuilder(); 
          
 17:         sb.Append(SELECT_CUSTOMERS_BASE_SQL);

          
 18:    

          
 19:         sb.Append(" and
City = @City "); 
          
 20:         Parameters.Add("City",
City); 
          
 21: 

          
 22:         sb.Append(" and
State = @State "); 
          
 23:         Parameters.Add("State",
State); 
          
 24: 

          
 25:         Sql = sb.ToString();

          
 26:     }

          
 27: }
        

The disadvantage is that inheriting from this class binds you into an inheritance hierarchy, which may not be a good thing (see inheritance vs. composition).  If you need to maintain a pure inheritance hierarchy, use the interface instead, or hide the implementation of this class in an internal Property.

Filter Objects

In many cases, you probably expose a common lightweight object to the UI layer for representing a “filter” to the database.  In reality, this is nothing more than a simple Data Transfer Object (DTO) that has properties representing all the ways the data can be filtered.

A common pattern I use is to take a Filter DTO object into the Query object’s constructor and build the SQL from it dynamically:

          
  1: publicclass SiteLocatorQuery
: SqlQuery 
          
  2: {

          
  3:     privateconststring SELECT_SITES_SQL
= .. 
          
  4: 

          
  5:     public SiteLocatorQuery(SiteLocatorFilter
filter) 
          
  6:     {

          
  7:         Filter = filter;

          
  8:     }

          
  9: 

          
 10:     public SiteLocatorFilter
Filter { get; privateset;
} 
          
 11: 

          
 12:     publicoverridevoid DoBuild() 
          
 13:     {

          
 14:         var sb = new StringBuilder(); 
          
 15:         sb.Append(SELECT_SITES_SQL);

          
 16:       

          
 17:         if (
Filter.IsRecent ) 
          
 18:         { 

          
 19:            sb.Append(" and
IsRecent = @IsRecent "); 
          
 20:            Parameters.Add("IsRecent",
1); 
          
 21:         }

          
 22:         if (
Filter.BrandID > 0 ) 
          
 23:         {

          
 24:            sb.Append(" and
BrandID = @BrandID "); 
          
 25:            Parameters.Add("BrandID",
filter.BrandID); 
          
 26:         }

          
 27: 

          
 28:         //
etc...
          
 29: 

          
 30:         Sql = sb.ToString();

          
 31:     }    

          
 32: }
        

This has the advantage of hiding the complexity of how the SQL is built up (or the fact that we are using raw SQL at all) from the UI layer.  I normally isolate my “Query” objects to a namespace in my MyCompany.Data dll, requiring a reference to the Filter objects (and not the other way around).  Plus, the light-weight DTOs can be used to pass data in and out of the UI layer very easily, as in the case of using messaging or web services.

So I’ve got my ISqlQuery interface coded … how do I use it?

Once you have a reference to the IDatabase interface, you can simply call the RunningQuery(ISqlQuery query) method to get a reference to an IDbStatement interface.  The method will call the Build() method on your interface and use the Sql and Parameters properties to populate the IDbStatement appropriately.  Once you get the IDbStatement back, you can then proceed just as you would have otherwise.

          
  1: public IEnumerable<Customer>
FindCustomersByFilter(CustomerFilter filter) 
          
  2: {

          
  3:     var query = new CustomerQuery(filter); 
          
  4:     this.Database 
          
  5:         .RunningQuery(query)

          
  6:         .QueryForResults(row => new Customer()); //
row mapping omitted
          
  7: }
        

Better late than never, eh?  Due to a crazy series of events in my life (both personally and professionally), I’ve had to put blogging on a hold for a short time.  Well, I’m back baby!  Today I’m going to continue my series on the latest Miado release.

In this post, I will discuss the use of DataSet (both generic and typed) with Miado.

Plain ol’ DataSet

If you really want to use a DataSet object, it’s dead-simple easy with Miado.  It’s just like using the Miado API for the IDbStatement, except that you don’t need to map the Result Set to a custom business object.  You just need to call the QueryForDataSet() method on the IDbStatement.

          
  1: public DataSet
FindBlogEntriesByBlog(int blogID) 
          
  2: {

          
  3:     return
          
  4:         this.Database 
          
  5:             .ExecutingSql(SELECT_BLOG_ENTRIES_BY_BLOG_ID_SQL)

          
  6:             .AddParameter("BlogID",
blogID) 
          
  7:             .QueryForDataSet();

          
  8: }
        

Typed DataSets

If you weren’t aware, Typed DataSet classes were introduced in 2.0 version of the .Net framework to compensate for some of the shortcomings of the original DataSet object.  Typed DataSets inherit from the DataSet class, but allow for strong typing on the rows and columns contained in the DataSet.  So instead of having to access the column values in the rows through a Dictionary key lookup, the column values now are exposed as strongly-typed properties on the Typed DataSet object itself.

On the QueryForDataSet() method detailed above, Miado exposes an optional generic typed version of the method that let’s you define the type of DataSet that will be returned.  QueryForDataSet<T>() can be used to return a strongly-typed DataSet object since T is constrained to be a subclass of DataSet.

          
  1: public BlogEntryDataSet
FindBlogEntriesByBlog(int blogID) 
          
  2: {

          
  3:     return
          
  4:         this.Database 
          
  5:             .ExecutingSql(SELECT_BLOG_ENTRIES_BY_BLOG_ID)

          
  6:             .AddParameter("BlogID",
blogID) 
          
  7:             .QueryForDataSet<BlogEntryDataSet>();

          
  8: }
        

DataTable

Not surprisingly, you can also retrieve a DataTable from the IDbStatement instead of a DataSet if you are only interested in a single table’s result set.  Simply call QueryForDataTable() instead of QueryForDataSet().

          
  1: public DataTable
FindBlogEntriesByBlog(int blogID) 
          
  2: {

          
  3:     return
          
  4:         this.Database 
          
  5:             .ExecutingSql(SELECT_BLOG_ENTRIES_BY_BLOG_ID_SQL)

          
  6:             .AddParameter("BlogID",
blogID) 
          
  7:             .QueryForDataTable();

          
  8: }
        

Thoughts on DataSet

I consider myself to be Alt.Net, so by law I’m required to tell you not to use DataSet.  It’s funny though – I like to play devil’s advocate a lot and ask the question as to why we don’t use it more often.  I’m just as guilty as the next person in creating my share of dumb Data Transfer Objects (DTOs) that directly represent database tables.  In doing so, I am forced to manually map the columns in the result set to properties on the DTO.  Why not skip that effort and just let the DataSet (typed or regular) handle that?  It’s already built into the framework after all.  And if you’ve ever played with Rails – isn’t an ActiveRecord object effectively the same thing as a Typed DataSet???

I guess it boils down to control.  I don’t like letting go of the classes I create and can easily refactor and manipulate without having to employ or depending on tooling to do so.  It’s a personal choice.  I don’t think I’d turn my nose down at a developer who chooses to use DataSets.  That being said, I can’t remember the last time I’ve done so.

Coming up next!

In my next post (whenever that may be), I will discuss how you can use Miado to build dynamic queries.

This is part 4 in a series about the latest release of Miado.  In my last post, I discussed about creating an IDbStatement from the IDatabase interface.  In this post, I will start to discuss the main methods exposed by the IDbStatement interface.

Adding Parameters

Adding parameters to the IDbStatement is really easy.  It is accomplished simply by calling the AddParameter() method with a name/value pair.  The name should match the parameter name declared in the SQL statement and the value is what will be substituted during the query execution.  Optionally, you can also set the DBType and/or parameter direction.  If the DBType is not set, it will be inferred by the DbProvider implementation based the type of the parameter value.  The parameter direction is assumed to be an input parameter unless explicitly declared.  This routine should be very familiar to anyone who has ever done traditional ADO.Net development.

Like most other methods on the IDbStatement interface, the AddParameter() method returns a reference to itself so it can be chained with other method calls on the IDbStatement interface.  Example:

          
  1: privatestaticreadonlystring INSERT_ADDRESS_SQL
= 
          
  2:     "insert
into Address(Address1, Address2, City, State, ZipCode) " + 
          
  3:     "values(@Addr1,
@Addr2, @City, @State, @ZipCode)"; 
          
  4: 

          
  5: publicvoid SaveAddress(Address
addr) 
          
  6: {

          
  7:     this.Database 
          
  8:         .ExecutingSql(INSERT_ADDRESS_SQL)

          
  9:         .AddParameter("Addr1",
addr.Address1) 
          
 10:         .AddParameter("Addr2",
addr.Address2) 
          
 11:         .AddParameter("City",
addr.City, DbType.String) // explicitly set DbType
          
 12:         .AddParameter("State",
addr.State) 
          
 13:         .AddParameter("ZipCode",
addr.ZipCode) 
          
 14:         .ExecuteNonQuery();

          
 15: }
        

If you really want total control over the parameter, you can get a reference to the actual DbParameter object using the Action<DbParameter> method signature of AddParameter().

          
  1: publicvoid UpdateUser(User
user) 
          
  2: {

          
  3:     this.Database 
          
  4:         .ExecutingSql(UPDATE_USER_SQL)

          
  5:         .AddParameter(dbParm => 

          
  6:         {

          
  7:             dbParm.ParameterName = "Email"; 
          
  8:             dbParm.Value = user.Email;

          
  9:         }) //
AddParameter(Action<DbParameter> dbParmAction)
          
 10:         .AddParameter(dbParm => 

          
 11:         { 

          
 12:             dbParm.ParameterName = "UserID"; 
          
 13:             dbParm.Value = user.UserID;

          
 14:             dbParm.DbType = DbType.Int32;

          
 15:             dbParm.ParameterDirection.Input;

          
 16:         }) //
dbParm is a DbParameter
          
 17:         .ExecuteNonQuery();

          
 18: }
        

Insert/Update/Delete

Anytime you want to execute a SQL statement that does not return a result set, you can call the ExecuteNonQuery() method (you probably already realized this fact from previous examples).  I’ve thought about adding explicit Save(), Update(), and Delete() methods to the API for clarity sake, but since I’m not providing an ORM, these methods would only be information and could not be guaranteed to perform their exact intended action.  In other words, they would merely wrap the ExecuteNonQuery() method, so you could call the Save() method to in fact execute a “delete from User where UserID = @ID” SQL statement with no problems.  I would be interested to see what other people thought about this change in the comments.  Does the readability of Save(), Update(), and Delete() outweigh the need to validate whether the right one is called?  Should there be validation against the raw SQL when one of these methods is called (e.g. explicitly checking the SQL string for “INSERT” when Save() is called)?  The validation method option is the route I’m leaning.

Creating Custom Business Objects

When you call QueryForResults() or QueryForOne(), you must use a generic type to declare the type of object that will be created from each row in the result set.  Your job will be to create an object for each row as the cursor moves forward in each iteration by mapping the values from the columns in the result set row.  Most of the time, this will be a custom business object.  However, it could be something as simple as an int if you are just returning a count(*).  Both these method types take a delegate that passes in an IResultSetRow interface (which merely wraps a DbDataReader) and return an instance of the generic type you declared.  The IResultSetRow interface has both typed  - using generics GetValue<T>() - and non-typed - GetValue() - methods that can be used to retrieve values using ordinals or by column name.

If your return type is simple or will not likely be re-used, you can use a lambda expression to create the returned object.

          
  1: privatestaticreadonly SELECT_USER_COUNT_SQL
= "select count(*) from Users"; 
          
  2: 

          
  3: publicint FindUserCount() 
          
  4: {

          
  5:     return
          
  6:         this.Database 
          
  7:             .ExecutingSql(SELECT_USER_COUNT_SQL)

          
  8:             .QueryForOne<int>(row
=> row.GetValue<int>(0)); 
          
  9: }
        

Alternatively, you can create a true delegate method that satisfies the signature required by the QueryForOne() and QueryForResults() methods and pass a reference to the delegate.

          
  1: public IEnumerable<BlogEntry>
FindBlogEntriesByBlog(int blogID) 
          
  2: {

          
  3:     return
          
  4:         this.Database 
          
  5:             .ExecutingSql(SELECT_BLOG_ENTRIES_BY_BLOG_ID_SQL)

          
  6:             .AddParameter("BlogID",
blogID) 
          
  7:             .QueryForResults<BlogEntry>(CreateBlogEntry);

          
  8: }

          
  9: 

          
 10: private BlogEntry
CreateBlogEntry(IResultSetRow row) 
          
 11: {

          
 12:     returnnew BlogEntry 
          
 13:     {

          
 14:         BlogEntryID = row.GetValue<int>("BlogEntryID"), 
          
 15:         Text = row.GetValue<string>("BlogText") 
          
 16:         //
rest of mapping ommitted
          
 17:     };

          
 18: }
        

In my next post, I will describe how to use the IDbStatement to return our old friend DataSet.

This is part 3 in a series about the new release of Miado.  If you want, you can go back and see Part 1 and Part 2 where I talk about creating an IDatabase reference.  In this part, I will discuss how to use the IDatabase to create an IDbStatement.

IDbStatement

The IDbStatement interface is the main working component of the Miado API.  You need to use this interface to run raw SQL or to execute a stored procedure.  Once you get a handle on the interface (from the IDatabase interface), you can begin “building” the statement that will be run against the DB.  Most of the methods on the interface return a reference to itself, so the method calls can be chained to form a fluent-type interface.

Executing SQL

Most of the time, I use raw SQL to execute my DB statements.  The ExecutingSql() method on the IDatabase interface returns an IDbStatement reference.

          
  1: publicclass ProductRepository
: IProductRepository 
          
  2: {

          
  3:     privatestaticreadonlystring SELECT_PRODUCT_BY_ID
= 
          
  4:         "select
ProductID, Name, ProductNumber, Color, ListPrice, ProductModel " + 
          
  5:         "from
Products " + 
          
  6:         "where
ProductID = @ID"; 
          
  7: 

          
  8:     //
more SQL 
          
  9: 

          
 10:     public ProductRepository(IDatabase
db) 
          
 11:     {

          
 12:         this.Database
= db; 
          
 13:     }

          
 14: 

          
 15:     public IDatabase
Database 
          
 16:     {

          
 17:         get; 
          
 18:         privateset; 
          
 19:     }

          
 20: 

          
 21:     public Product
Load(int productID) 
          
 22:     {

          
 23:         IDbStatement dbStmt = this.Database.ExecutingSql(SELECT_PRODUCT_BY_ID); 
          
 24:         dbStmt.AddParameter("ID",
productID); 
          
 25:         return dbStmt.QueryForOne<Product>(CreateProduct); 
          
 26:     }

          
 27: 

          
 28:     //
more CRUD methods
          
 29: 

          
 30:     private Product
CreateProduct(IResultSetRow row) 
          
 31:     {

          
 32:         //
implementation omitted...
          
 33:     }

          
 34: } 
        

As I said before, since the methods on the IDbStatement return themselves, you can chain the calls.  In line 21-26, you could change the Load() method to read like this:

          
  1: public Product
Load(int productID) 
          
  2: {

          
  3:     return
          
  4:         this.Database 
          
  5:             .ExecutingSql(SELECT_PRODUCT_BY_ID)

          
  6:             .AddParameter("ID",
productID) 
          
  7:             .QueryForOne<Product>(CreateProduct);

          
  8: }
        

Stored Procedures

Stored Procedures are built up in a similar fashion, except you need to call the CallingStoredProcedureNamed() method to load the SP.

          
  1: publicclass EmployeeRepository
: IEmployeeRepository 
          
  2: {

          
  3:     public EmployeeRepository(IDatabase
db) 
          
  4:     { 

          
  5:         this.Database
= db; 
          
  6:     }

          
  7:  

          
  8:     public IDatabase
Database 
          
  9:     {

          
 10:         get; 
          
 11:         privateset; 
          
 12:     }

          
 13: 

          
 14:     public IEnumerable<Employee>
FindEmployeesByManager(int mgrID) 
          
 15:     {

          
 16:        return
          
 17:           this.Database 
          
 18:               .CallingStoredProcedureNamed("uspGetManagerEmployees") 
          
 19:               .AddParameter("ManagerID",
mgrID) 
          
 20:               .QueryForResults<Employee>(CreateEmployee);

          
 21:     }

          
 22: 

          
 23:     private Employee
CreateEmployee(IResultSetRow row) 
          
 24:     {

          
 25:         //
implementation omitted
          
 26:     }

          
 27: }
        

Registered Queries

I showed in my last post how you can use the IDatabase interface to “register” queries.  You can easily retrieve them in the IDbStatement interface by using LoadQueryRegisteredAs() method, which will load the corresponding SQL.

          
  1: public IEnumerable<State>
FindAllStates() 
          
  2: {

          
  3:     return
          
  4:         this.Database 
          
  5:             .LoadQueryRegisteredAs("SelectStates") 
          
  6:             .QueryForResults<State>(

          
  7:                 row => new State 
          
  8:                 { 

          
  9:                     Abbreviation = row.GetValue<string>("StateCode"), 
          
 10:                     Name = row.GetValue<string>("Name") 
          
 11:                 });

          
 12: }                
        

Running Custom Queries

There is one more way to “load” a query in the IDbStatement interface, and that is by calling the RunningQuery() method, and passing in an object that implements the ISqlQuery interface.  That is new functionality to this release and probably deserves its own blog post, so I will cover that later.

In my next post, I will discuss how the IDbStatement executes and discuss the different kinds of return types available, and how you can create custom business objects from the query result set.

This is part 2 in a series on the new updates to the Miado API.  You can read the first part in the series here.  In this post, I am going to discuss some of the new features available when configuring Miado.

Query Registration

I’ve had a couple of clients who’ve had a requirement where they wanted to store their SQL in a single location rather than spread across the Repository objects as embedded SQL.  In fact, one client put all their SQL in .sql files and stored them on the file system.  I had never seen this before, but after working with it for a while I definitely warmed up on the idea.  I definitely saw some advantages for doing this:

• Versioning – it’s very easy to isolate changes to individual SQL statements, and you can take advantage of all the benefits of using a version control system, like labeling, diffs, branching, etc.
• Testing - you can open the SQL files directly in your DB management software to test the queries (as opposed to cutting and pasting out your source code, where you have to remove code formatting like string concatenations)
• Collaboration – you can easily share the queries with a DBA, who can help tweak them or run profiling tools against them
• Isolation – all your queries are stored in a common well-known place

So I added the capability in Miado to “register” queries by name.  You can either do this manually or by pointing to files or a directory on the file system.  The IQueryRegistry interface controls the registration and retrieval of stored queries.  To get an access to this interface, you need to declare an Action<IQueryRegistry> delegate to configure itself.  The delegate is passed in via a method on the IDatabase interface.

Registering Queries Manually

The easiest way to register queries is by setting name/value pairs:

          
  1: var db = new SqlServerDatabase(connString); 
          
  2: db.ConfigureQueryRegistry(queryRegistry => 

          
  3:     {

          
  4:         string name
= "SelectStates"; 
          
  5:         string sql
= "select StateCode, Name from States"; 
          
  6:         queryRegistry.RegisterQuery(name, sql);

          
  7: 

          
  8:         string name1
= "SelectUserByID"; 
          
  9:         string sql1
= "select UserID, Email " + 
          
 10:                       "from
Users " + 
          
 11:                       "where
UserID = @ID"; 
          
 12:         //
NamedQuery is a simple name/value pair object
          
 13:         var namedQuery = new NamedQuery(name1,
sql1); 
          
 14:         queryRegistry.RegisterQuery(namedQuery);

          
 15:     });
        

Registering Queries From Files

Alternately, you can register queries from files on the file system.  There are multiple ways to do this.  First of all, you can start at a selected directory and optionally pass a Predicate to select only certain files.  From the resulting files, you need to build a NamedQuery list from each individual file.

          
  1: var db = new SqlServerDatabase(connString); 
          
  2: db.ConfigureQueryRegistry(queryRegistry =>

          
  3:     {

          
  4:         //
start looking in the "sql" directory for files named *.sql
          
  5:         queryRegistry.RegisterQueriesFromPath(

          
  6:             "sql", 
          
  7:             fileInfo => String.Compare(fileInfo.Extension, ".sql")
== 0, 
          
  8:             fileInfo => 

          
  9:             {

          
 10:                 string queryName
= fileInfo.Name.Substring(0, fileInfo.Name.IndexOf('.')); 
          
 11:                 string sql
= File.ReadAllText(fileInfo.FullName); 
          
 12:                 returnnew NamedQuery[]
{ new NamedQuery(queryName, sql) }; 
          
 13:             });

          
 14:     });
        

You can also pass in the specific files you want processed:

          
  1: var db = new SqlServerDatabase(connString); 
          
  2: db.ConfigureQueryRegistry(queryRegistry => 

          
  3:     {

          
  4:         //
find the files yourself
          
  5:         string[]
files = Directory.GetFiles("sql", "*.sql",
SearchOption.AllDirectories); 
          
  6:         queryRegistry.RegisterQueriesFromFiles(

          
  7:             files, 

          
  8:             fileInfo =>

          
  9:             {

          
 10:                 string queryName
= fileInfo.Name.Substring(0, fileInfo.Name.IndexOf('.')); 
          
 11:                 string sql
= File.ReadAllText(fileInfo.FullName); 
          
 12:                 returnnew NamedQuery[]
{ new NamedQuery(queryName, sql) }; 
          
 13:             });

          
 14:     });
        

Be Smart

Obviously, you need to be careful about exposing the raw SQL in any directory that can be compromised.  If you are using a web app, make sure it is not in a publicly visible folder.  If you are using a rich client app, you might want to think about using Isolated Storage as your underlying query repository.

In my next post, I will show how to use the IDbStatement to run queries, including those registered in the IQueryRegistry.

I released a new version of Miado on CodePlex last night, so I thought I’d spend a couple of blog posts explaining how to use the API.  Consider this post as the first in a multi-part series on how to use the newest version.

Basics – Creating an IDatabase

The first thing you need to do is get a handle on an IDatabase.  The interface (and its corresponding implementation) serves as the entry point of the API.  Obviously, the easiest way to do so would be to directly new one up.  The Database constructor takes in a DbProviderFactory object and a connection string.

          
  1: string connString
= 
          
  2:     "Data
Source=localhost;Initial Catalog=MyDatabase; User ID=MyUser; Password=Password1"; 
          
  3: IDatabase db = new Database(SqlClientFactory.Instance,
connString);
        

I’ve created a few sub-classes of the Database class that take care of the provider initialization (using the corresponding DbProviderFactory implementations provided in the .Net Framework) and just take in a connection string:

• OdbcDatabase
• OleDatabase
• OracleDatabase
• SqlServerDatabase

e.g.

          
  1: string connString
= 
          
  2:     "Data
Source=localhost;Initial Catalog=MyDatabase; User ID=MyUser; Password=Password1"; 
          
  3: IDatabase db = new SqlServerDatabase(connString);
        

Using Miado with a Depedency Injection Container

I’m a big fan of Dependency Injection, so I normally create a reference to the IDatabase in my application start event and store it in the DI container. 

          
  1: publicclass Global
: System.Web.HttpApplication, IContainerAccessor 
          
  2: {

          
  3:     public IUnityContainer
Container 
          
  4:     {

          
  5:         get; 
          
  6:         protectedset; 
          
  7:     }

          
  8: 

          
  9:     protectedvoid Application_Start() 
          
 10:     {

          
 11:         this.InitializeContainer(); 
          
 12:     }

          
 13: 

          
 14:     protectedvoid InitializeContainer() 
          
 15:     {

          
 16:         var container = new UnityContainer(); 
          
 17:         

          
 18:         string connString
= ConfigurationManager.ConnectionStrings["MyDatabase"].ConnectionString; 
          
 19:         //
create IDatabase instance and store it in the container
          
 20:         var db = new SqlServerDatabase(connString); 
          
 21: 

          
 22:         container.RegisterInstance<IDatabase>(db);

          
 23: 

          
 24:         //
create a Repository object - IDatabase will injected in it
          
 25:         container.RegisterType<IUserRepository, UserRepository>();

          
 26: 

          
 27:         //
rest of the container initialization omitted ...
          
 28: 

          
 29:         Container = container;

          
 30:     }

          
 31: }
        

When I create my repository objects, I design them to take a reference to the IDatabase in the constructor.

          
  1: publicclass UserRepository
: IUserRepository 
          
  2: {

          
  3:     public UserRepository(IDatabase
db) 
          
  4:     {

          
  5:         this.Database
= db; 
          
  6:     }

          
  7: 

          
  8:     public IDatabase
Database 
          
  9:     {

          
 10:         get; 
          
 11:         privateset; 
          
 12:     }

          
 13: 

          
 14:     //
CRUD methods omitted
          
 15: 

          
 16: }

          
 17: 
        

The nice thing about the DI container is that it will automatically inject a reference to the IDatabase instance I registered when it resolves the Repository reference.

          
  1: IContainerAccessor accessor = HttpContext.Current.ApplicationInstance as IContainerAccessor; 
          
  2: 

          
  3: //
IDatabase is resolved and injected in UserRepository constructor
          
  4: IUserRepository userRepository = accessor.Container.Resolve<IUserRepository>();
        

If you don’t want to use a DI container, you can accomplish a similar de-coupling by hiding the IDatabase creation behind a Factory object.

          
  1: publicstaticclass DatabaseFactory 
          
  2: {

          
  3:     privatestaticreadonly IDatabase
_db = 
          
  4:         new SqlServerDatabase(ConfigurationManager.ConnectionStrings["MyDatabase"].ConnectionString); 
          
  5: 

          
  6:     publicstatic IDatabase
CreateDatabase() 
          
  7:     {

          
  8:         return _db; 
          
  9:     }

          
 10: }
        

In my next post, I will discuss how to use the IDatabase interface to register queries (a new feature in Miado).

When I first jumped into C# programming, one of the biggest points of confusion for me was in understanding delegates.  You see, Java had no real similar concept.  So the idea of function pointers didn’t really register with me.  I saw some really weird syntax for event handlers that looked like this:

               1: myButton.Clicked
+= MyButton_Clicked;

               2:  

               3:
              //
...
            

               4:  

               5:
              private MyButton_Clicked(object sender,
EventArgs e) 

               6: {

               7:
              //
do something
            

               8: }

Eventually, I caught on that because the function called MyButton_Clicked satisfied the signature required by the OnClick event, it could be added as an event handler to the event.

Aha!  Delegates are nothing more than “interfaces” at the method (as opposed to class) level.  So even though I understood what delegates were, I still didn’t see a widespread use for them outside event handlers.  Sure, I saw examples where they were used, but they all seemed very contrived to me. 

Enter in lambda expressions

Lambda expressions were introduced in C# 3.0.  I’ve said it before, while lambda expressions are new to .Net, they are not even close to being a new concept in programming languages.  They have been around forever.  Basically, it’s a terse syntax for defining anonymous delegates.  In .Net, they were really a simpler way to interact with LINQ.  Now you no longer had to go through the ceremony of creating an explicit method just to satisfy the compiler.  This “inline” function call was especially useful in simple delegate calls, as in a Predicate:

               1: var
myList = new List<Person>();

               2:
              //
...
            

               3: Person
chris = myList.Find(person => person.FirstName == "Chris");

I don’t know why, but I really latched on to lambda expressions in a  way I never did with delegates.  Which is actually a little weird, since I’ve heard numerous complaints that the lambda expression syntax is too confusing for the average developer. 

Changing the way I code

Now, lambda expressions have really changed the way I approach programming.  I’ll give an example from Miado.  I wanted to add support to Miado for creating typed DataSet objects (in addition to regular DataSet objects).  I added support for a querying for a DataSet using generics, where the generic type had to be a class derived from DataSet:

               1:
              public
              virtual T
QueryForDataSet<T>() where T : DataSet

I wanted to have one common method that handles creating both types of DataSets (the ol’ DRY – i.e. “Don’t Repeat Yourself”).  Here’s the rub - when using a DataAdapter to fill the DataSet, the method actually is just a little different from using a regular DataSet versus a typed one.  It’s not that different, but enough to make you have to handle it two different ways.  Previously, I probably would’ve created a template method or maybe handled it through an interface.  But to use interfaces would require an interface to define the method and two separate classes to implement the varying implementations.  That’s a lot of work to accomplish this seemingly simple task.

Hmm … if I could just pass in the method  that I want to call, I can solve this problem much easier.  Enter in my good friend Action<T> to the rescue! 

Action<T>

Action<T> is a delegate method.  It takes in an instance of the generic T type defined in its signature and has no return value.  So it’s a callback method that performs some action (and thus cleverly named).  I love this delegate.  It’s really great for implementing simple one line functions via a lambda expression.  The syntax becomes very terse without having to build up all the ceremony just to satisfy the compiler.

Implementation

Actually, Action is overloaded so you can pass in multiple arguments.  In my case, I am using two arguments to the method (i.e. Action<T,U>).  Here is the way I implemented it:

               1:
              private T
QueryForDataSetUsingCustomDataAdapterFillFunction<T>(

               2: Action<DbDataAdapter,
T> adapterFillFunction) where T : DataSet

               3: {

               4: T
ds = CreateEmptyDataSet<T>();

               5:  

               6:
              using (
DbConnection conn = this.Database.CreateConnection()
)

               7: {

               8: conn.Open();

               9:  

               10:
              using (
DbCommand cmd = conn.CreateCommand() )

               11: {

               12: cmd.CommandText
= this.CommandText;

               13: cmd.CommandType
= this.CommandType;

               14:  

               15:
              if ( this.Parameters
!= null )

               16: {

               17: cmd.Parameters.AddEnumeration(this.Parameters);

               18: }

               19:  

               20:
              using (
DbDataAdapter adapter = this.Database.CreateDataAdapter()
)

               21: {

               22: adapter.SelectCommand
= cmd;

               23: adapterFillFunction(adapter,
ds);

               24: }

               25: }

               26: }

               27:  

               28:
              return ds;

               29: }

               30:  

               31:
              public
              virtual DataSet
QueryForDataSet()

               32: {

               33:
              return QueryForDataSetUsingCustomDataAdapterFillFunction<DataSet>(

               34: (adapter,
ds) => adapter.Fill(ds));

               35: }

               36:  

               37:
              public
              virtual T
QueryForDataSet<T>() where T : DataSet

               38: {

               39:
              return QueryForDataSetUsingCustomDataAdapterFillFunction<T>(

               40: (adapter,
ds) => adapter.Fill(ds, ds.Tables[0].TableName));

               41: }

Basically, I made it so that the common method takes in a function that, given a DataAdapter and a DataSet, does some work on those objects.  So the two public methods pass in a different implementation of the Fill() method on the DataAdapter.  Like I said before, it’s kind of like using interfaces for methods.  The common method (in line 23) calls the Action method to perform its specific function by passing back the current DataAdapter and DataSet.

Conclusion

Again, lambda expressions have changed the way I approach programming.  Once you get a handle on the syntax, it’s a great tool to have in your toolbox!

Tonight we are going to have another meeting of the Atlanta alt.net user group.  We are meeting at Manuel’s Tavern again, but we are supposed to be in a different room this time.  I know the last meeting at Manuel’s was a little hard to find (if you weren’t there, last time they put us in a side room off another room that was holding a meeting, which had closed its outer doors to the rest of the restaurant). 

This week were are going to be in the “Eagle’s Nest” room, which is located on the other side of the restaurant off the main dining area on its southern side.  Look for the small stairs in the corner of the room.

We are going to be discussing the book, “Agile Estimating and Planning” by Mike Cohn.  If you haven’t read the book, it’s no big deal.  We will be discussing lots of other things, too.  

Hope to see you there!

In case you’ve been living in a cave on Mars with your fingers in your ears for the last year, you’ve probably heard we just ended a little election here in the United States.  I’m not big on the whole politics scene, so I’ll spare you much further discussion on the subject, except that I just don’t *get* why people blindly pledge their allegiance to extremist political views (no matter which side they’re on).   Yet people by the millions are quick to eat up the junk spooned out by people like Rush Limbaugh, (fellow Cornell alum) Keith Olberman, (fellow Cornell alum) Ann Coulter, Sean Hannity, Bill O’Reilly, etc.  If you ask me, they’re all equally wackos.

The same phenomena happens in the software development community.  We as an industry are very divided on what we hold to be the best technology, whether it be operating systems, programming languages, IDEs, frameworks, etc. 

Maybe it’s the middle child in me or the fact that I’m a Libra, but I tend to take a more centrist view on things.

I’ll share two quick items about my past:

1. At one time, I was a snobby Java programmer at the height of the dot-com boom.  If you told me during the early part of this decade that I would be making my living doing (egad!) Microsoft development for a living, I would have called you bat-shit crazy.  But a funny thing happened … I got exposed to C# on a project I was on (i.e. it was mandated we use it), and it turned out to be (IMO) a better version of Java.  And .Net was a wonderful development environment!  It wasn’t at all like going to “the dark side” as I would have been led to believe by my Java brethren.
2. I’ve known my friend Brad, another software developer, since college.  Though neither of us were CS majors, somehow we both ended up in the software development field.  Here we are close to 15 years removed from school and both have taken much different routes to get to where we are in our careers.  While I have toed the corporate line and always stuck to “enterprise” software development (i.e. Java and .Net), Brad has been fascinated with open source technologies, functional programming languages, alternative databases, and highly concurrent systems (way before any of these gathered mainstream momentum).  In short, about 180 degrees from my development background.  Now that he has moved to Atlanta, in the last few years he has been a great influence on me and my view of the software development world.  In fact, part of the reason I so quickly latched on to the new dynamic-language-type features introduced in .Net 3.0 (e.g. lambda expressions, closures, extension methods) was directly because of his influence since he had been telling me about them in other languages for so long.  Once I finally was exposed to them first hand, I quickly understood where he was coming from.

The lesson I’ve learned is to keep an open mind when it comes to software development.  Too many times, we let pre-conceived notions and technology prejudices influence our decisions.  (Want to know a dirty little secret?  I like Vista … a lot, actually.)

I’m finally reading the Pragmatic Programmer (I know, I know, lay off me!), and though I’ve heard it re-told many times by many people, there is a classic adage in the book about learning a new programming language every year.  There’s a reason it’s re-told so often.  It’s because it’s really excellent advice.  If nothing else, it will help broaden your horizon when it comes to tackling problems in your day-to-day programming language.   It can open your mind to an entirely different way of thinking.  As humans, we’re creatures of habit.  We need something to shake things up occasionally.

The reason I’m writing this post now is that within the last few weeks, I’ve been exposed to technologists wielding “Golden Hammers”.  If you’re not familiar with the term, it refers to people who get so focused on a particular technology, they think it will solve every problem thrown at them.  “Sharepoint can do that!”  “You need to employ a 100% SOA so your website can scale, no matter how many users you are projecting!”  “Let’s write an iPhone app for this niche blue-collar customer base!”  When you have this Golden Hammer, everything looks like a nail.

It’s perfectly fine to have your convictions.  Being passionate about something, whatever that thing may be, is one of the highest highs you can get in life.  But don’t stick your head in the sand when it comes to technology.  There is no “one technology to rule them all”.  Try to be objective in your decisions.  Use common sense.  Weigh trade-offs for choosing one technology over another.  Practice pragmatism.  And use the right tool for the job.