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c#entity-frameworklinq
Lost_In_Library
Lost_In_Library

Reputation: 3493

Create Linq Expression ( Combine Expressions )

I'm using entity framework 6.1.3 and .net framework 4.5.1 with C# lang.

What I want to do is; I want to combine expressions with if-else statements.
Here is my expression 

Expression<Func<Article, bool>> expression = 
    q => (!newsDayStart.HasValue || q.PublishedOn >= newsDayStart) &&
         (!newsDayEnd.HasValue || q.PublishedOn <= newsDayEnd) &&
         (!categoryId.HasValue || q.CategoryId == categoryId.Value) &&
         (string.IsNullOrEmpty(searchText) || q.Title.Contains(searchText) &&
         (!isActive != null || q.IsActive == isActive.Value));

to 

Expression<Func<Article, bool>> expression = ......;

if ( newsDayStart.HasValue )
{
   //Obviosly += this statement will not work.
   expression += q => q.PublishedOn > = newsDayStart

}

//TODO write other if else statements...

//Send expression
_context.Articles.Where(expression).Count();

Upvotes: 0

Views: 139

Answers (1)

Chris Wyatt
Chris Wyatt

Reputation: 142

If this is specifically for use with EF queries then you might find it easier to chain Where() calls to achieve the same effect.

Expression<Func<Article, bool>> expression = ......;

//Send expression
var query = _context.Articles.Where(expression)

if ( newsDayStart.HasValue )
{
    query = query.Where(q => q.PublishedOn > = newsDayStart);
}

query.Count();

*Edit

You could try using this third-party library, PredicateBuilder http://www.albahari.com/nutshell/predicatebuilder.aspx

Upvotes: 2

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