Entity Framework–> Change Database

I was working with Entity Frameworks over the weekend when I ran into some sloppy programming on Microsoft’s part.  I made a project that uses Entity Frameworks to connection to Northwind.  I then added method to change the database at runtime like so:

public class NorthwindFactory
{
    public static void ChangeDatabase(String newDatabaseName)
    {
        using (NorthwindEntities entities = new NorthwindEntities())
        {
            entities.Connection.ChangeDatabase(newDatabaseName);
        }
    }
}

When I checked out intellisense on the ChangeDatabase method, there was nothing to indicate anything unusual.

image

When I invoked the method, I got the following exception:

image

Sure enough, when I go to MSDN help online, ChangeDatabase() is not supported in 4.5 and 4.0, but it is supported in 3.5. 

image

This is a clear violation of the Liskov Substitution Principle.  It is a also sloppy – they could have marked it obsolete or, at least, changed the XML code comments to reflect the fact that it is not supported.  Instead, they left it up to the developer to get the exception the first time s/he invokes it.

So instead of using the ChangeDatabase() method, I needed to use the SqlConnectionStringBuilder and EntityConnectionStringBuilder like so:

SqlConnectionStringBuilder sqlConnectionStringBuilder = 
    new SqlConnectionStringBuilder();
sqlConnectionStringBuilder.DataSource = ".";
sqlConnectionStringBuilder.InitialCatalog = newDatabaseName;
sqlConnectionStringBuilder.IntegratedSecurity = true;

EntityConnectionStringBuilder entityConnectionStringBuilder = 
    new EntityConnectionStringBuilder();
entityConnectionStringBuilder.Metadata = 
    @"res://*/NorthwindModel.csdl|res://*/NorthwindModel.ssdl|res://*/NorthwindModel.msl";
entityConnectionStringBuilder.Provider = "System.Data.SqlClient";
entityConnectionStringBuilder.ProviderConnectionString = 
    sqlConnectionStringBuilder.ConnectionString;

The problem is that I can’t use that entityConnectionStringBuilder inside of the using block of the Entity that I want to change:

image

So to switch databases, I have to drop the “using” statement.  The below code snippet works

NorthwindEntities entities = new NorthwindEntities();
SqlConnectionStringBuilder sqlConnectionStringBuilder = 
    new SqlConnectionStringBuilder();
sqlConnectionStringBuilder.DataSource = ".";
sqlConnectionStringBuilder.InitialCatalog = newDatabaseName;
sqlConnectionStringBuilder.IntegratedSecurity = true;

EntityConnectionStringBuilder entityConnectionStringBuilder = 
    new EntityConnectionStringBuilder();
entityConnectionStringBuilder.Metadata = 
    @"res://*/NorthwindModel.csdl|res://*/NorthwindModel.ssdl|res://*/NorthwindModel.msl";
entityConnectionStringBuilder.Provider = "System.Data.SqlClient";
entityConnectionStringBuilder.ProviderConnectionString = 
    sqlConnectionStringBuilder.ConnectionString;

entities = new NorthwindEntities(entityConnectionStringBuilder.ConnectionString);

I am not sure Microsoft thought this one through…

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