LINQ - take x objects from database for each object property value

Question

I have an entity:

public class Component
{
    public Guid Id { get; set; }
    public string Name { get; set; }
    public ProductType Type { get; set; }
}

ProductType

public enum ProductType
{
    Harddrive = 1,
    GraphicCard,
    ComputerCase,
}

I'm trying to get list of Product that contains 15 random items (5 per ProductType) in single LINQ.

ComputerCase, GraphicCard and Harddrive inherts from same base class

For now I have something like that:

        var response = db.Components
            .Select(x => new Product
            {
                Id = x.Id,
                Name = x.Name,
                Type = x.Type,
            }).ToList();

but I have no idea how could I achive what I need. Can anyone help me with that?

Answer 1

Make groups of Components with the same ProductType . From the resulting collection of groups take the first Component in the group. From that result take the first 5, items.

var result = myComponents.                    // take the collection of Components
    .GroupBy(component => component.Type)     // group this into groups of components with same Type
    .Select(group => group.FirstOrDefault())  // from every group take the first element
    .Take(5)                                  // take only the first five

Of course, if you really want a proper random, you'll have to fetch all Component groups to local memory and use RND to extract random groups and random element from each selected group