Question

I am trying to set up a simple one-to-many relationship where a list can have zero or more tasks and a task must have a list associated. I want to assure this behavior with a unit test but I can’t figure out how the association has to be, so that the test will fail (later I will use an ExpectedExceptionAttribute, but I don’t even know which exception will be thrown yet).

The Task can be successfully submitted, but I would like to see Linq complain about a missing List reference:

[TestMethod]
public void SavingTaskWithoutListFails()
{
    var task = new Task() { Title = "Test Task", Description = "This is the task description." };
    Db.Tasks.InsertOnSubmit(task);
    Db.SubmitChanges();            
}

My classes and associations look like this:

[Table]
public class Task
{
    [Column(AutoSync = AutoSync.OnInsert, DbType = "Int NOT NULL IDENTITY", IsDbGenerated = true)]
    public int TaskId { get; set; }

    [Column(IsPrimaryKey = true)]
    public string Title { get; set; }

    [Column]
    public string Description { get; set; }

    [Column]
    public int ListId { get; set; }

    private EntityRef<List> _list;

    [Association(Storage = "_list", ThisKey = "ListId")]
    public List List
    {
        get { return _list.Entity; }
        set { _list.Entity = value; }
    }
}

and this:

[Table]
public class List
{
    [Column(AutoSync = AutoSync.OnInsert, DbType = "Int NOT NULL IDENTITY", IsDbGenerated = true)]
    public int ListId { get; set; }

    [Column(IsPrimaryKey = true)]
    public string Title { get; set; }

    private EntitySet<Task> _tasks;

    [Association(Storage = "_tasks", OtherKey = "TaskId")]
    public EntitySet<Task> Tasks
    {
        get { return _tasks; }
        set
        {
            if (_tasks == null)
            {
                _tasks = new EntitySet<Task>();
            }
            _tasks.Assign(value);
        }
    }
}

Can anyone help with the correct association or a hint how to achieve the desired behavior?

Answer 1

You should use [Column(CanBeNull = false)] for association columns to achieve that.

Edit:

[Table]
public class Task
{
    [Column(IsPrimaryKey = true, AutoSync = AutoSync.OnInsert, DbType = "Int NOT NULL IDENTITY", IsDbGenerated = true)]
    public int TaskId { get; set; }

    [Column]
    public string Title { get; set; }

    [Column]
    public string Description { get; set; }

    [Column(CanBeNull =  false)]
    public int ListId { get; set; }

    private EntityRef<List> _list;

    [Association(Storage = "_list", ThisKey = "ListId", IsForeignKey = true, OtherKey = "ListId")]
    public List List
    {
        get { return _list.Entity; }
        set { _list.Entity = value; }
    }
}

[Table]
public class List
{
    [Column(IsPrimaryKey = true, AutoSync = AutoSync.OnInsert, DbType = "Int NOT NULL IDENTITY", IsDbGenerated = true)]
    public int ListId { get; set; }

    [Column]
    public string Title { get; set; }

    private EntitySet<Task> _tasks;

    [Association(Storage = "_tasks", OtherKey = "TaskId", ThisKey = "ListId")]
    public EntitySet<Task> Tasks
    {
        get { return _tasks; }
        set
        {
            if (_tasks == null)
            {
                _tasks = new EntitySet<Task>();
            }
            _tasks.Assign(value);
        }
    }
}

I moved IsPrimaryKey to Id instead of Title for both tables, set one side of an association as IsForeignKey=true and fill both ThisKey and OtherKey for both sides of association. When I tried to add new task without ListId value SubmitChanges throwed SlqCEException with following message: A foreign key value cannot be inserted because a corresponding primary key value does not exist. [ Foreign key constraint name = FK_Task_List ]