Question

I have a filter that I use across many methods:

Expression<Func<Child, bool>> filter = child => child.Status == 1;

(actually is more complex than that)

And I have to do the following

return db.Parents.Where(parent => parent.Status == 1 &&
                                  parent.Child.Status == 1);

where the condition is the same as in the filter above.

I want to reuse the filter in this method. But I don’t know how. I tried

return db.Parents.Where(parent => parent.Status == 1 &&
                                  filter(parent.Child));

but an Expression can’t be used as a method

Answer 1

If you want to combine expressions and still be able to use linq-to-sql, you may want to have a look at LinqKit. It walks inside your expression and replaces all the function calls by their contents before the sql conversion.

This way you’ll be able to use directly

return db.Parents
       .AsExpandable()
       .Where(parent => parent.Status == 1 && filter(parent.Child));