Temporarily set DbContext's CommandTimeout

Question

I know I can set the DbContext's CommandTimeout for all queries with something like this:

public class YourContext : DbContext
{
    public YourContext() : base("YourConnectionString")
    {
        // Get the ObjectContext related to this DbContext
        var objectContext = (this as IObjectContextAdapter).ObjectContext;

        // Sets the command timeout for all the commands
        // to 2 min instead of the default 30 sec
        objectContext.CommandTimeout = 120;
    }
}

However, I want to keep the default 30 sec, except for one single method that takes a bit longer.

How should I change this for this single query?

I did try to use:

public void doSomething(){
    // The using had another reason, but in this case it also
    // automatically disposes of the DbContext
    using(IMyDbContext = delegateDbContext()){
        ((IObjectContextAdapter)usingDb).ObjectContext.CommandTimeout = 120;

        ... // myQuery
    }
}

Everything works perfectly, until I run my UnitTest with a Mock-DbContext (and yes, I did set my delegate to this Mock-DbContext). It gives me an InvalidCastException:

System.InvalidCastException: Unable to cast object of type
'Castle.Proxies.FakeMyDbContextProxy' to type
'System.Data.Entity.Infrastructure.IObjectContextAdapter'.

Answer 1

That's because you're relying on an implementation detail (the fact that your IMyDbContext also implements IObjectContextAdapter) that you're not supposed to know about. In your unit test, the IMyDbContext instance is actually a proxy generated by the mocking framework, and doesn't implement IObjectContextAdapter.

Since the CommandTimeout wouldn't make sense for this fake DbContext, I suggest you try to cast and set the CommandTimeout only if the cast succeed:

var objectContextAdapter = usingDb as IObjectContextAdapter;
if (objectContextAdapter != null)
    objectContextAdapter.ObjectContext.CommandTimeout = 120;

This way, the CommandTimeout will be set in the real execution environment, but not in the unit test (which doesn't matter, since the mock doesn't actually query the DB)

---

EDIT: actually, a better and cleaner option would be to modify IMyDbContext to expose a way to set the CommandTimeout:

interface IMyDbContext
{
    ...

    int CommandTimeout { get; set; }
}


class MyDbContext : IMyDbContext
{
    ...

    public int CommandTimeout
    {
        get { return ((IObjectContextAdapter)this).ObjectContext.CommandTimeout; }
        set { ((IObjectContextAdapter)this).ObjectContext.CommandTimeout = value; }
    }
}

And now you can just do:

usingDb.CommandTimeout = 120;

without worrying about the actual type of the context. The mocking framework would just generate a dummy implementation for this property.

Answer 2

And to touch on the original question of setting the Timeout for a single statement. The straight-forward approach is sometimes the best. Assuming you've exposed the CommandTimeout as suggested above (great idea), then in your function:

var originalTimeout = _dbContext.CommandTimeout;
_dbContext.CommandTimeout = 120;
// do something relevant
_dbContext.CommandTimeout = originalTimeout;