I have a simple Parent Child table in a database like so
CREATE TABLE [Parent](
[Id] [int] IDENTITY(1,1) NOT NULL,
[Name] [nvarchar](256) NOT NULL)
ALTER TABLE [Parent] ADD CONSTRAINT [PK_Parent_Id] PRIMARY KEY ([Id])
CREATE TABLE [Child](
[Id] [int] IDENTITY(1,1) NOT NULL,
[ParentId] [int] NOT NULL,
[Name] [nvarchar](256) NOT NULL)
ALTER TABLE [Child] ADD CONSTRAINT [PK_Child_Id] PRIMARY KEY ([Id])
ALTER TABLE [Child] ADD CONSTRAINT [FK_Child_Parent_ID]
FOREIGN KEY([ParentId]) REFERENCES [Parent] ([Id])
The data that I have in them is
Parent Table
Id Name
1 John
Child Table
Id ParentId Name
1 1 Mike
2 1 Jake
3 1 Sue
4 1 Liz
These tables are mapped to Parent
and Child
C# objects using the Linq-2-SQL designer in Visual Studio with no non standard options.
I made a simple test program to query all child with their parents
public partial class Parent
{
static int counter = 0;
//default OnCreated created by the linq to sql designer
partial void OnCreated()
{
Console.WriteLine(string.Format("CreatedParent {0} hashcode={1}",
++counter , GetHashCode()));
}
}
class Program
{
static void Main(string[] args)
{
using (var db = new SimpleDbDataContext())
{
DataLoadOptions opts = new DataLoadOptions();
opts.LoadWith<Child>(c => c.Parent);
db.LoadOptions = opts;
var allChildren = db.Childs.ToArray();
foreach (var child in allChildren)
{
Console.WriteLine(string.Format("Parent name={0} hashcode={1}",
child.Parent.Name, child.Parent.GetHashCode()));
}
}
}
}
The output of the above program is
CreatedParent 1 hashcode=53937671
CreatedParent 2 hashcode=9874138
CreatedParent 3 hashcode=2186493
CreatedParent 4 hashcode=22537358
Parent name=John hashcode=53937671
Parent name=John hashcode=53937671
Parent name=John hashcode=53937671
Parent name=John hashcode=53937671
As you can see a Parent
object was created for every Child
in the database only to be discarded eventually.
Questions:
- Why does Linq-2-Sql create these unnecessary extra
Parent
objects ? - Are there any options to avoid creation of extra
Parent
objects ?