Query: improve identifier validation so that we don't throw exception for "insufficient identifiers" when there is only one collection in the projection

[maumar]

Example scenario:

await using var context = new BlogContext();
await context.Database.EnsureDeletedAsync();
await context.Database.EnsureCreatedAsync();

await context.Blogs.Select(b => new
{
    b.Id,
    Names = new[] { b.Name }.Concat(b.Posts.Select(c => c.Title)).ToList()
}).ToListAsync();

public class BlogContext : DbContext
{
    public DbSet<Blog> Blogs { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        => optionsBuilder
            .UseSqlServer("Server=localhost;Database=test;User=SA;Password=Abcd5678;Connect Timeout=60;ConnectRetryCount=0;Encrypt=false")
            .LogTo(Console.WriteLine, LogLevel.Information)
            .EnableSensitiveDataLogging();
}

public class Blog
{
    public int Id { get; set; }
    public string Name { get; set; }

    public List<Post> Posts { get; set; }
}

public class Post
{
    public int Id { get; set; }
    public string Title { get; set; }

    public Blog Blog { get; set; }
}

This throws Unable to translate a collection subquery in a projection since either parent or the subquery doesn't project necessary information required to uniquely identify it and correctly generate results on the client side. This can happen when trying to correlate on keyless entity type.

In theory we should be ok here because there is no second collection in the projection, so we should know how to bucket the results only based on identifiers of the parent (Blogs).

[roji]

@maumar putting this on the backlog FYI.