put where predicate in a variable

Question

I am using Entity Framework code first and I have code like this:

var foos = context.Foos.Where(f => f.Bar == "Hello World").ToList();

Using an SQL profiler, I see that the script run against the database contained a WHERE statement, as expected.

But when I put the Where predicate in a variable:

Func<Foo, bool> predicate = f => f.Bar == "Hello World");
var foos = context.Foos.Where(predicate).ToList();

the resulting SQL command no longer contains a WHERE statement.

Is there a way that this can work?

What does it include instead of a WHERE?

John Saunders
– John Saunders

2015-03-05 03:00:37 +00:00
Commented Mar 5, 2015 at 3:00 — John Saunders
– John Saunders, Commented Mar 5, 2015 at 3:00

Aducci · Accepted Answer · 2015-03-05 02:32:04Z

1

Change to Expression<Func<Foo, bool>>

Expression<Func<Foo, bool>> predicate = f => f.Bar == "Hello World";

answered Mar 5, 2015 at 2:32

Aducci

26.8k8 gold badges67 silver badges69 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

AechoLiu · Accepted Answer · 2015-03-05 03:04:51Z

0

LinqKit could solve this kind issues. It can be obtained by nuget.

An example about using PredicateBuilder of LinqKit.

IQueryable<Product> SearchProducts (params string[] keywords)
{
  var predicate = PredicateBuilder.False<Product>();

  foreach (string keyword in keywords)
  {
    string temp = keyword;
    predicate = predicate.Or (p => p.Description.Contains (temp));
  }
  return dataContext.Products.Where (predicate);
}

How it works

var predicate = PredicateBuilder.True <Product> ();

// is just a shortcut for this:
Expression<Func<Product, bool>> predicate = c => true;

edited Mar 5, 2015 at 3:04

answered Mar 5, 2015 at 2:59

AechoLiu

18.6k11 gold badges108 silver badges122 bronze badges

Collectives™ on Stack Overflow

put where predicate in a variable

2 Answers 2

Comments

How it works

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

How it works

Comments

Your Answer

Sign up or log in

Post as a guest

Related