Does using a lambda expression passed into a method slow down an Entity Framework query?

Question

I have a method:

public static void GetObjects()
{
    using(MyContext context = new MyContext())
    {
         var objects = context.Bars.Where(b => b.Prop1         


        

Answer 1

As I discovered in my own question, .Where(o => whereFunc(o)) is not the same as .Where(whereFunc) in the Entity Framework.

The first one, .Where(Expression>) works like any other linq call, simply appending the expression to the expression tree.

In the second case, .Where(Func>), it will compile and evaluate the linq call (which so far is just context.Bars) before applying the whereFunc predicate.

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So, to answer your question, the second one is much slower because it is pulling the entire Bars table into memory before doing anything with it. Using .Where(o => whereFunc(o)) instead should fix that

(or, as Mark suggests, change the type of whereFunc to Expression>, which Func is implicitly convertible to)