How to bind Ninject to [Obsolete] constructor?

Question

In my submodule, I have:

public class CustomerRepository : ICustomerRepository
{
    private readonly IDBEngine _dbEngine;
    [CanBeNull] private readonly string _overriddenDebugEmail;

    [Obsolete("Use the other constructor")]
    public CustomerRepository(IDBEngine dbEngine)
    {
        _dbEngine = dbEngine;
        _overriddenDebugEmail = null;
    }
    // ReSharper disable once UnusedMember.Global
    public CustomerRepository(IDBEngine dbEngine, IDebugConstants debugConstants)
    {
        _dbEngine = dbEngine;
        _overriddenDebugEmail = debugConstants.OverridingDebugEmail;
    }
    ...

The problem is, when I simply update the submodule without implementing IDebugConstants, I get the following runtime error:

Error activating IDebugConstants

No matching bindings are available, and the type is not self-bindable.

I want Ninject to bind to the Obsolete constructor if IDebugConstants is not implemented. But it refuses to because of the obsolete attribute. In theory I could remove the Obsolete attribute, but I want it to show that that code should no longer exist once all old programs using the submodule have been updated.

Is there some way to make Ninject ignore the Obsolete attribute?

Or am I going about this entirely wrong somehow?

Owen Pauling Owen Pauling · Accepted Answer · 2019-06-12T11:08:00

You can do this by adding the [Inject] attribute to your [Obsolete] constructor.

The reason for this is how the constructor scoring is implemented. Specifically this section of the Score method:

if (directive.Constructor.HasAttribute(this.settings.InjectAttribute))
{
    return int.MaxValue;
}

if (directive.Constructor.HasAttribute(typeof(ObsoleteAttribute)))
{
    return int.MinValue;
}

You will see that if the constructor has the [Obsolete] attribute then it is given the minimum possible score. But prior to that, if the constructor has the [Inject] attribute then it will be given the highest possible score.

This doesn't help in the specific case you mentioned where you want a conditional binding when IDebugConstants is not implemented, but it does answer "Is there some way to make Ninject ignore the Obsolete attribute?"

How to bind Ninject to [Obsolete] constructor?

1 Answers