Conditionally Exclude Child Property in Entity Framework Query - entity-framework

Question

Given the following object graph
public class Bar {
public Guid Id {get;set;}
public string SomeBar {get;set;}
}
public class Foo {
public Guid Id {get;set;}
public string FooString {get; set;}
public IList<Bar> Bars {get;set;}
}
How do I conditionally exclude the Bars property properly so that Entity Framework doesn't load the entire object graph?
// my thoughts
public Task<Foo> GetFooByIdAsync(Guid id, bool includeBars)
{
var query = _db.Foos.Where(f => f.Id == id);
if(!includeBars)
{
return query.Select(f=> new Foo{
Id = f.Id,
FooString = f.FooString
}).ToListAsync();
} else {
return query.ToListAsync();
}
}

Answer 1

Just conditionally add the Include(f => f.Bars) into the query expression. Like this:
using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations.Schema;
using System.Data.Common;
using System.Data.Entity;
using System.Data.Entity.ModelConfiguration;
using System.Data.SqlClient;
using System.Linq;
using System.Threading.Tasks;
namespace ConsoleApp8
{
public class Bar
{
public Guid Id { get; set; }
public string SomeBar { get; set; }
}
public class Foo
{
public Guid Id { get; set; }
public string FooString { get; set; }
public IList<Bar> Bars { get; set; }
}
class Db: DbContext
{
public DbSet<Foo> Foos { get; set; }
public DbSet<Bar> Bar { get; set; }
public async Task<Foo> GetFooByIdAsync(Guid id, bool includeBars)
{
var query = (IQueryable<Foo>)Foos.AsNoTracking();
if (includeBars)
{
query = query.Include(f => f.Bars);
}
query = query.Where(f => f.Id == id);
var results = await query.ToListAsync();
return results.FirstOrDefault();
}
}
class Program
{
static void Main(string[] args)
{
Database.SetInitializer(new DropCreateDatabaseAlways<Db>());
using (var db = new Db())
{
db.Database.Initialize(false);
db.Database.Log = m => Console.WriteLine(m);
var r1 = db.GetFooByIdAsync(Guid.Empty, false).Result;
var r2 = db.GetFooByIdAsync(Guid.Empty, true).Result;
}
Console.WriteLine("Hit any key to exit");
Console.ReadKey();
}
}
}
outputs
Opened connection asynchronously at 9/11/2017 11:37:26 PM -05:00
SELECT
[Extent1].[Id] AS [Id],
[Extent1].[FooString] AS [FooString]
FROM [dbo].[Foos] AS [Extent1]
WHERE [Extent1].[Id] = #p__linq__0
-- p__linq__0: '00000000-0000-0000-0000-000000000000' (Type = Guid, IsNullable = false)
-- Executing asynchronously at 9/11/2017 11:37:26 PM -05:00
-- Completed in 22 ms with result: SqlDataReader
Closed connection at 9/11/2017 11:37:26 PM -05:00
Opened connection asynchronously at 9/11/2017 11:37:26 PM -05:00
SELECT
[Project1].[C1] AS [C1],
[Project1].[Id] AS [Id],
[Project1].[FooString] AS [FooString],
[Project1].[C2] AS [C2],
[Project1].[Id1] AS [Id1],
[Project1].[SomeBar] AS [SomeBar]
FROM ( SELECT
[Extent1].[Id] AS [Id],
[Extent1].[FooString] AS [FooString],
1 AS [C1],
[Extent2].[Id] AS [Id1],
[Extent2].[SomeBar] AS [SomeBar],
CASE WHEN ([Extent2].[Id] IS NULL) THEN CAST(NULL AS int) ELSE 1 END AS [C2]
FROM [dbo].[Foos] AS [Extent1]
LEFT OUTER JOIN [dbo].[Bars] AS [Extent2] ON [Extent1].[Id] = [Extent2].[Foo_Id]
WHERE [Extent1].[Id] = #p__linq__0
) AS [Project1]
ORDER BY [Project1].[Id] ASC, [Project1].[C2] ASC
-- p__linq__0: '00000000-0000-0000-0000-000000000000' (Type = Guid, IsNullable = false)
-- Executing asynchronously at 9/11/2017 11:37:26 PM -05:00
-- Completed in 2 ms with result: SqlDataReader
Closed connection at 9/11/2017 11:37:26 PM -05:00
Hit any key to exit