I tried to store and reload objects and their references between each other. The problem is when I reload the data from the database the references are not set correctly.
Here is an example code which describes the problem. I comment the the expcted state and the real state of the output in the code.
[Table(Name = "ClassA")]
public class ClassA
{
public ClassA()
{
LinksToClassB = new EntitySet<ClassB>();
}
[Column(IsPrimaryKey = true, IsDbGenerated = true, AutoSync = AutoSync.OnInsert, DbType = "Int NOT NULL IDENTITY")]
public int ID { get; set; }
[Association]
public EntitySet<ClassB> LinksToClassB { get; set; } //=> 1 to n cardinality
[Association]
public ClassB OneLinkToClassB { get; set; }//=> 1 to 1 cardinality
}
[Table(Name = "ClassB")]
public class ClassB
{
[Column(IsPrimaryKey = true, IsDbGenerated = true, AutoSync = AutoSync.OnInsert, DbType = "Int NOT NULL IDENTITY")]
public int ID { get; set; }
[Column(CanBeNull = true)]
public string Name { get; set; }
}
public class DatabaseContext : DataContext
{
public Table<ClassA> ClassATable;
public Table<ClassB> ClassBTable;
public DatabaseContext(string connection) : base(connection) { }
}
[TestClass]
public class Test
{
string path = @"F:\Temp\Testspace - Forum Database\database.mdf";//path to database
[TestMethod]
public void TestMethod()
{
//creates Database
DatabaseContext context = new DatabaseContext(path);
if (context.DatabaseExists())//Delete if exists
{
context.DeleteDatabase();
}
context.CreateDatabase();
ClassB b1 = new ClassB(); b1.Name = "name 1";
ClassB b2 = new ClassB(); b2.Name = "name 2";
ClassB b3 = new ClassB(); b3.Name = "name 3";
ClassA a = new ClassA();
//now the references will be added to the object a
//in 1-n references
a.LinksToClassB.Add(b1);
a.LinksToClassB.Add(b2);
a.LinksToClassB.Add(b3);
//and the has-one reference (OneLinkToClassB)
a.OneLinkToClassB = b1;
context.ClassATable.InsertOnSubmit(a);
context.SubmitChanges(); //store in database
//now the database will be reloaded
context = new DatabaseContext(path);
//Check if all ClassB objects were correctly stored and reloaded
foreach (ClassB x in context.ClassBTable)
{
Console.WriteLine(x.ID + "; " + x.Name);
/*
-> expected output:
1; name 1
2; name 2
3; name 3
-> real output
1; name 1
2; name 2
3; name 3
-> check!
*/
}
//check if all ClassA objects were correctly stored and reloaded
foreach (ClassA x in context.ClassATable)//context.ClassATable has only one entry
{
Console.WriteLine("check of entitys set");
//check of 1-n references
foreach (ClassB b in x.LinksToClassB)
{
Console.WriteLine(x.ID + " has a link to " + b.ID + ", " + b.Name);
/*
-> expected output:
1 has a link to 1, name 1
1 has a link to 2, name 2
1 has a link to 3, name 3
-> real output
1 has a link to 1, name 1
-> doesn't match...
*/
}
Console.WriteLine("check of single link");
//check of 1-1 reference
Console.WriteLine(x.ID + " has a link to " + x.OneLinkToClassB.ID + ", " + x.OneLinkToClassB.Name);
/*
-> expected output:
1 has a link to 1, name 1
-> real output
this line throws an NullReferenceException
*/
}
}
}
I hope anyone can give me a hint how to solve this bug in my code :)
as @Nick said the "parent / child association(s) are missing". Here now the complete changed code:
[Table(Name = "ClassA")]
public class ClassA
{
public ClassA()
{
LinksToClassB = new EntitySet<ClassB>();
}
[Column(IsPrimaryKey = true, IsDbGenerated = true)]
private int ID;
[Association(ThisKey = "ID", OtherKey = "ClassAId")]
private EntitySet<ClassB> LinksToClassB;//=> 1 to n cardinality
public void addLink(ClassB x)
{
LinksToClassB.Add(x);
x.setLink(this);
}
public HashSet<ClassB> getLinks()
{
HashSet<ClassB> collection = new HashSet<ClassB>();
foreach(ClassB x in LinksToClassB)
{
collection.Add(x);
}
return collection;
}
}
[Table(Name = "ClassB")]
public class ClassB
{
private EntityRef<ClassA> _classA = default(EntityRef<ClassA>);
[Column(IsPrimaryKey = true, IsDbGenerated = true, AutoSync = AutoSync.OnInsert, DbType = "Int NOT NULL IDENTITY")]
public int ID { get; set; }
[Column(CanBeNull = true)]
public string Name { get; set; }
[Column(CanBeNull = false)]
private int ClassAId { get; set; }
[Association(ThisKey = "ClassAId", OtherKey = "ID", IsForeignKey = true)]
private ClassA ClassA
{
get
{
return _classA.Entity;
}
set
{
_classA.Entity = value;
}
}
private ClassA getLink()
{
return _classA.Entity;
}
public void setLink(ClassA x)
{
_classA.Entity = x;
}
}
public class DatabaseContext : DataContext
{
public Table<ClassA> ClassATable;
public Table<ClassB> ClassBTable;
public DatabaseContext(string connection) : base(connection) { }
}
[TestClass]
public class Test
{
string path = @"F:\Temp\Testspace - Forum Database\database.mdf";//path to database
[TestMethod]
public void TestMethod()
{
//creates Database
DatabaseContext context = new DatabaseContext(path);
if (context.DatabaseExists())//Delete if exists
{
context.DeleteDatabase();
}
context.CreateDatabase();
ClassB b1 = new ClassB(); b1.Name = "name 1";
ClassB b2 = new ClassB(); b2.Name = "name 2";
ClassB b3 = new ClassB(); b3.Name = "name 3";
ClassA a = new ClassA();
//now the references will be added to the object a
//in 1-n references
a.addLink(b1);
a.addLink(b2);
a.addLink(b3);
context.ClassATable.InsertOnSubmit(a);
context.SubmitChanges(); //store in database
//now the database will be reloaded
context = new DatabaseContext(path);
//Check if all ClassB objects were correctly stored and reloaded
foreach (ClassB x in context.ClassBTable)
{
Console.WriteLine(x.ID + "; " + x.Name);
/*
-> expected output:
1; name 1
2; name 2
3; name 3
-> real output
1; name 1
2; name 2
3; name 3
-> check!
*/
}
//check if all ClassA objects were correctly stored and reloaded
foreach (ClassA x in context.ClassATable)//context.ClassATable has only one entry
{
Console.WriteLine("check of entitys set");
//check of 1-n references
foreach (ClassB b in x.getLinks())
{
Console.WriteLine(b.ID + " has a link to " + b.ID + ", " + b.Name);
/*
-> expected output:
1 has a link to 1, name 1
1 has a link to 2, name 2
1 has a link to 3, name 3
-> real output
1 has a link to 1, name 1
1 has a link to 2, name 2
1 has a link to 3, name 3
-> check!
*/
}
}
}
}