Create Multiple Objects Single LINQ EF Method

Question

List<MyObject> objects = await item.tables.ToAsyncEnumerable()
                               .Where(p => p.field1 == value)
                               .Select(p => new MyObject(p.field1,p.field2))
                               .ToList();

^ I have something like that, but what i'm wondering, is there anyway way to add a second object creation, in the same select? eg. new MyObject(p.field3,p.field4) ? and add it to the same list? order does not matter.

I know could do this with multiple calls to database or splitting up lists into sections, but is there way to do this in single line?

Answer 1

You could create it as a tuple.

List<Tuple<MyObject1, MyObject2>> = query.Select(x => Tuple.Create(
    new MyObject1
    {
        // fields
    },
    new MyObject2
    {
        //fields
    }))
    .ToList();

From my testing in Linqpad, it seems that this will only hit the database once.

Alternatively, you could just select all the fields you know you'll need from the database to create both:

var myList = query.Select(x => new { FieldA = x.FieldA, FieldB = x.FieldB }).ToList(); //hits db once
var object1s = myList.Select(x => new MyObject1(x.FieldA));
var object2s = myList.Select(x => new MyObject1(x.FieldB));
var bothLists = object1s.Concat(object2s).ToList();

Answer 2

What you'd want to do is use the SelectMany method in linq. Which will select all the items from an array. The array can be created anonymously as seen below.

List<MyObject> objects = await item.tables.ToAsyncEnumerable()
                               .Where(p => p.field1 == value)
                               .SelectMany(p => new []{new MyObject(p.field1,p.field2), new MyObject(p.field3,p.field4)})
                               .ToList();

Hope that solves you problem!