Custom LINQ extension for make join

Question

Let's say I need create custom expression to make some manipulation with IQueryable<x> and IQueryable<y>. Regretfully I do not have idea how to implement this. This is my try:

public static IQueryable<T> JoinQueries<T>(this IQueryable<T> query, IQueryable<T> expr)
        {
           if (query == null)
                throw new ArgumentNullException("query");
            //Here we make Join for x and and return result something like this:
           query = from a in query join b in expr on a.Id equals b.Id select a;
            return query;
        }

Or say other words I need result like this:

IQueryable <somevalue> x = query.CustomJoinExtension(Iqueryablevalue);

I would assume `expr` needs to be `Expression>`. In order to access `Id` you need to use a generic constraint `where T : SomeEntity` — Callum Linington, Jul 28 '15 at 10:03
You want to combine two different queries on the same type? Or did i misunderstand something? — KeyNone, Jul 28 '15 at 10:04
@CallumLinington, thanks, may you provide some simple example please, I'm completele new to use extensions and expressions. — andrey.shedko, Jul 28 '15 at 10:05
@BastiM, yes, this sound wrong that's why I'm asking how to handle this situation. — andrey.shedko, Jul 28 '15 at 10:06

score 1 · Answer 1 · answered Jul 28 '15 at 10:07

1

Something like this:

public static IQueryable<T> JoinQueries<T>
(this IQueryable<T> query, IQueryable<T> expr) where T : IHasId
{
    if (query == null)
        throw new ArgumentNullException("query");
    //Here we make Join for x and and return result something like this:
    query = from a in query join b in expr on a.Id equals b.Id select a;
    return query;
}

public interface IHasId
{
    int Id { get; set; }
}

answered Jul 28 '15 at 10:07

Davor Zlotrg

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if this is for use in the Entity Framework, the class restriction should have "class" added, otherwise EF cannot understand the query: http://stackoverflow.com/a/21172754/1117815 – felipe Dec 22 '16 at 14:28

Custom LINQ extension for make join

1 Answers1