How to use multi expression methods in Entity Framework query

Question

I use same EF query multiple times in my application so I need something like this:

private Expression<Func<Student, bool>> StudentIsActive()
{
    return (x) => !x.IsDeleted && x.ItemsNumber > 0 && x.Sort > 0 && x.Status == StudentStatus.Active;
}

private Expression<Func<Student, bool>> StudentIsBusy()
{
    return (x) => x.Mode == ModeType.Busy && x.Jobs.Count() > 0;
}

I want to use same logic in multiple of my queries, like:

 var students = context.Orders.Where(x => StudentIsActive() && StudentIsBusy()).ToList();

Does any one have any idea about this? how could I use AND or OR logic between expression methods?

If you only need to `And` them together, just add another `Where` clause, for example: `context.Orders.Where(StudentIsActive()).Where(StudentIsBusy())` — DavidG, Mar 17 '17 at 16:42

score 0 · Answer 1 · answered Mar 17 '17 at 16:53

I am not in home so I cant test itt buy I think you can transport these methods into extensions methods of IQueryable like this:

  public static class Ext
    {
       public static IQueryable<MainActivity.Student> StudentIsActive(this IQueryable<MainActivity.Student> @this)
        {
            return @this.Where(x => !x.IsDeleted && x.ItemsNumber > 0 && x.Sort > 0 && x.Status == StudentStatus.Active);
        }

        public static IQueryable<MainActivity.Student> IsBusy(this IQueryable<MainActivity.Student> @this)
        {
            return @this.Where(x.Mode == ModeType.Busy && x.Jobs.Count() > 0);
        }

    }

And use it like:

context.Orders.StudentIsActive().IsBusy().ToList();

This only does "and" but not "or", it's also no different than my comment above. — DavidG, Mar 17 '17 at 16:59

score 0 · Answer 2 · answered Mar 17 '17 at 17:21

0

I usually find the easiest way to And/Or Expressions together is to use LinqKit. Once you've referenced that library you can do this:

//Or
var orPredicate = PredicateBuilder.Or(StudentIsActive(), StudentIsBusy());
var orders1 = context.Orders.AsExpandable().Where(orPredicate);

//And
var andPredicate = PredicateBuilder.And(StudentIsActive(), StudentIsBusy());
var orders2 = context.Orders.AsExpandable().Where(andPredicate);

answered Mar 17 '17 at 17:21

DavidG

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Could the person who downvoted this please explain? – DavidG Mar 17 '17 at 18:21

How to use multi expression methods in Entity Framework query

2 Answers2