Question

Could anyone explain to my why this is not working?

In the database we have Employees with an IdEmployee column. We also have some tables with foreign keys to that one.

Say we have something like this:

var employee = dataContext.Employees.First(<some predicate>); var someEntity = dataContext.SomeEntities.First(<some predicate>); 

Why does this not work:

var something = someEntity.SomeThings.First(t => t.Employee == employee); 

while this does:

var something = someEntity.SomeThings.First(t => t.IdEmployee == employee.IdEmployee); 

I don’t get it… Isn’t the first version supposed to work? The Employee entity is from the same datacontext…

Answer 1

It is a little bit tricky to know for sure when you have used names like SomeThings and someEntity, but what I believe is happening is that when you’re looking at someEntity.SomeThings, SomeThings is a collection of Employee entities. Thus, the t in your lambda expression will refer to an Employee object, giving you the ability to compare their properties.

Try the following

var something = someEntity.SomeThings.First(t => t.Equals(employee)); 

and see if that works better.

EDIT: Actually, the .Equals() syntax is better than the == I first proposed…

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EDIT2: As Sessiz Saas proposes, it is probably because of lazy loading. An alternate way of loading the employee objects is provided below:

var myThings = dataContext.Things.Include('employee'); 

However, remember that this could cause extra (and unnecessary, as you are able to do the job anyway) data calls.