Sort collection by first item of sub list in Entity Framework

Question

Is it possible to sort IQueryable collection by it\'s sub collections?

For example I have a Books collection. I also have an Authors<

Answer 1

The answer to your concrete question (after clarification that The authors should be ordered by name, and the books collection by previously ordered list of authors) is like this:

var query = db.Books
    .OrderBy(b => b.Authors.OrderBy(a => a.Name).Select(a => a.Name).FirstOrDefault());

which would generate a single SQL query like this:

SELECT
    [Project2].[Id] AS [Id],
    [Project2].[Title] AS [Title]
    FROM ( SELECT
        [Extent1].[Id] AS [Id],
        [Extent1].[Title] AS [Title],
        (SELECT TOP (1) [Project1].[Name] AS [Name]
            FROM ( SELECT
                [Extent2].[Name] AS [Name]
                FROM [dbo].[Author] AS [Extent2]
                WHERE [Extent1].[Id] = [Extent2].[BookId]
            )  AS [Project1]
            ORDER BY [Project1].[Name] ASC) AS [C1]
        FROM [dbo].[Book] AS [Extent1]
    )  AS [Project2]
    ORDER BY [Project2].[C1] ASC

Note that the books w/o author will be the first in the order.

Another way is to use Min function:

var query = db.Books
    .OrderBy(b => b.Authors.Min(a => a.Name));

with SQL translation:

SELECT
    [Project1].[Id] AS [Id],
    [Project1].[Title] AS [Title]
    FROM ( SELECT
        [Extent1].[Id] AS [Id],
        [Extent1].[Title] AS [Title],
        (SELECT
            MIN([Extent2].[Name]) AS [A1]
            FROM [dbo].[Author] AS [Extent2]
            WHERE [Extent1].[Id] = [Extent2].[BookId]) AS [C1]
        FROM [dbo].[Book] AS [Extent1]
    )  AS [Project1]
    ORDER BY [Project1].[C1] ASC