CODEWITHSUNDEEP
c#.netlinq-to-sqlpredicate
Dilberted
Dilberted

Reputation: 1172

Creating a predicate for the following where condition

I have looked at many posts but unable to find an answer to my question.

I have a lot of queries that are using the Where condition as below. In the code it looks quite ugly, so i thought of using a predicate (dont know whether it is possible or not).

.Where(i => i.Timestamp <= date.ToUniversalTime() && i.Timestamp >= yearStart.ToUniversalTime())

I want this to become or something like this

.WhereYearTotal(date)

so the condition can be evaluated within "WhereYearTotal" function.

Edited:

I have already tried the extension method but it does not seem to work inside a nested query such as:

var query = (from o in db.tableA
        select new {
           monthly =  db.tableA.WhereYearTotal(date),
}).FirstOrDefault();

I get a Null reference exception.

Upvotes: 0

Views: 290

Answers (4)

svick
svick

Reputation: 244787

Have a look at LINQKit. I will let you do exactly what you want.

Upvotes: 1

archil
archil

Reputation: 39501

Predicate is method passed as argument to Where. What you want is not a predicate, but extension method

namespace ExtensionMethods
{
    public static class MyExtensions
    {
        public static IEnumerable<MyClass> WhereYearTotal(this IEnuerable<MyClass> source, DateTime date)
        {
            return source.Where(i => i.Timestamp <= date.ToUniversalTime() && i.Timestamp >= yearStart.ToUniversalTime())
        }
    }   
}

Upvotes: 0

Strelok
Strelok

Reputation: 51451

Just write your own extension method for IQueryable:

public static IQueryable<TSource> WhereYearTotal<TSource>(
    this IQueryable<TSource> source,
    DateTime date ) {
    return source.Where(i => i.Timestamp <= date.ToUniversalTime() && i.Timestamp >= yearStart.ToUniversalTime());
}

Upvotes: 0

J.N.
J.N.

Reputation: 8421

This is done using extension methods. You need to create a static class and a static method for it.

static class MyHelper
{
    public static IEnumerable<T> WhereYearTotal(this IEnumerable<T> input, DateTime d)
    {
         return input.Where( ... )
    }
}

// usage : (the namespace for MyHelper must be in your using list)
myCollection.WhereYearTotal( DateTime.Now );

Upvotes: 0

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