Question

With the following DB schema:

CREATE TABLE master (
    id integer primary key autoincrement, 
    title text);
CREATE TABLE slave (
    id integer primary key autoincrement, 
    master_id integer not null, 
    title text, 
    foreign key (master_id) references master (id));

I created an sqlite database, which I then used to create an Entity Framework .edmx file.

Then I add a master and a slave record, which works fine, and then I try to remove the slave record, but that raises an exception and I don’t know why.

var ctx = new blaEntities();
var newMaster = master.Createmaster(0);
ctx.masters.AddObject(newMaster);

var newSlave = slave.Createslave(0, 0);
newMaster.slaves.Add(newSlave);

ctx.SaveChanges(); // works fine, both id and master_id properties of newMaster 
                   // and newSlave are then set with generated values.

newMaster.slaves.Remove(newSlave);

ctx.SaveChanges(); // InvalidOperationException is raised

The message of the exception is:

The operation failed: The relationship could not be changed because
one or more of the foreign-key properties is non-nullable. When a
change is made to a relationship, the related foreign-key property is
set to a null value. If the foreign-key does not support null values,
a new relationship must be defined, the foreign-key property must be
assigned another non-null value, or the unrelated object must be
deleted.

What am I doing wrong?

Edit:

Here is the generated by EF Createslave(...) method:

public static slave Createslave(global::System.Int64 id, global::System.Int64 master_id)
{
    slave slave = new slave();
    slave.id = id;
    slave.master_id = master_id;
    return slave;
}

Answer 1

There is still a slave object in your slave table that has no value set in the masterId column.

Try using ctx.DeleteObject(newSlave) to get rid of it.