更新父实体不会更新子实体

Question

Whether attaching parent entity to the context again and updating it should update the child entity? Am i missing something?

Or should I necessarily write the updating EF logic (in DAL) for the child entity?

This is my sample code model:

ChildEntity entityChild;
if (ParentEntity.ChildEntity.SingleOrDefault() != null)
    entityChild = ParentEntity.ChildEntity.SingleOrDefault();
else
{
    entityChild = new ChildEntity();
    ParentEntity.ChildEntity.Add(entityChild);
}

entityChild.ColumnA= txtA.Text;
entityChild.ColumnB= txtB.Text;

// Send entityParent for update
_objParent.Update(entityParent)

_objParent.Update() code:

context.vouchers.Attach(entityParent);
ObjectStateEntry objectState = context.ObjectStateManager.GetObjectStateEntry(entityParent);
objectState.ChangeState(System.Data.EntityState.Modified);
context.SaveChanges();

UPDATE (Parent Loading Code Sample)

    public ParentEntity GetById(int id)
    {
        using (var context = new DBEntities())
        {
            ParentEntity _entity = context.ParentEntity
                .Include("ChildEntity")
                .Where(e => e.parent_id == id);

            return (ParentEntity)_entity.SingleOrDefault()
        }
    }

Answer 1

EF only track changes from the point where it gets to know about the object. The most simple way to work with updates in EF is to load the existing object from the DB, update it and then save it back. In this case it means that you should load the ParentEntity object from the DB.

The other approach is to use Attach as you do. In that case you should first call attach the unchanged ParentEntity and then call ParentEntity.ChildEntity.Add(entityChild) .

Another alternative is to explicitly add the new ChildEntity directly to the DbContext, then you could simply set the foreign key value of the ChildEntity to the key value of the ParentEntity to make them connected.

Answer 2

You should load and update your entities inside the using statement - this way all the changes will be tracked by the Entity Framework:

using (var context = new DBEntities())
{
    // load and update entities
    // ....

    context.SaveChanges();
}

UPDATE - This is just an example, I'll keep it simple. I would create a service where I'd put my logic - something like this:

public class ParentService
{
    // other service methods here

    protected DBEntities CreateContext()
    {
        return new DBEntities();
    }

    public ParentEntity Update(int id, string columnA, string columnB)
    {
        ParentEntity _entity = null;

        using (var context = CreateContext())
        {
            bool isNew = false;

            _entity = context.ParentEntity
                .Include("ChildEntity")
                .SingleOrDefault(e => e.parent_id == id);

            ChildEntity entityChild = ParentEntity.ChildEntity.SingleOrDefault();

            if(entityChild == null)
            {
                entityChild = new ChildEntity();
                isNew = true;
            }

            entityChild.ColumnA = columnA;
            entityChild.ColumnB = columnB;

            if(isNew)
            {
                ParentEntity.ChildEntity.Add(entityChild);
            }

            context.SaveChanges();
        }

        return _entity;
    }
}

In the UI code:

string id = .....;
string columnA= txtA.Text;
strign columnB = txtB.Text;

var service = new ParentService();
ParentEntity parent = service.Update(id, columnA, columnB);