Overriding code-generated DbContext constructor

Question

Overriding code-generated DbContext constructor

.net asp.net-mvc c# connection-string entity-framework

Question

I'm sure I've done this before at some stage, but I can't figure out how to now! My scenario:

// This is generated from EDMX
public partial class HOLDbEntities : DbContext
{
    public HOLDbEntities()
            : base("name=HOLDbEntities")
        {
        }
}

Now, I want this connection string to be easily changeable (I want to Implement from the HOLDbEntities), so I need to override this constructor.

I've tried:

public partial class HOLDbEntities
{
    private const string _contextName = "HOLDbEntities";
    public static string ContextName { get { return _contextName; } }

    public HOLDbEntities()
        : base(ContextName)
    {
    }
}

But this throw an error:

HOLDbEntities already defines a member called "HOLDbEntities" with the same parameter types.

I can understand why this errors, but how would I stop the constructor being auto-generated in the first place in order to do what I'm trying to achieve?

Chris Dixon

Popular Answer

I up-voted the previous accepted answer because it is a fairly elegant way of doing it. However another approach would be to modify the T4 template that generates the dbContext Class.

When using EF DB first you have a .edmx file and under that you have an [Entity].Context.tt file. Go into that file and remove (or modify) the following code:

public <#=code.Escape(container)#>()
        : base("name=<#=container.Name#>")
    {
<#
if (!loader.IsLazyLoadingEnabled(container))
{
#>
        this.Configuration.LazyLoadingEnabled = false;
<#
}

foreach (var entitySet in container.BaseEntitySets.OfType<EntitySet>())
{
    // Note: the DbSet members are defined below such that the getter and
    // setter always have the same accessibility as the DbSet definition
    if (Accessibility.ForReadOnlyProperty(entitySet) != "public")
    {
#>
        <#=codeStringGenerator.DbSetInitializer(entitySet)#>
<#
    }
}
#>

now your context class will generate without a constructor, so you should be able to go and create one in an extended class.

Dylan Hayes

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Marc Gravell · Accepted Answer · 2/26/2013 11:59:23 AM

Accepted Answer

The best I can suggest is a factory method:

private HOLDbEntities(string contextName) : base(contextName) { }

public static HOLDbEntities Create() {
    return new HOLDbEntities(ContextName);
}

and use HOLDbEntities.Create() rather than new HOLDbEntities().

Marc Gravell

Overriding code-generated DbContext constructor

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