Question

This is my current code to update a field in database

private void SaveUser(User user)
{
   USER UserObj = _db.USERs.First(i => i.USER_ID == user.USER_ID);
   UserObj.NAME = user.NAME;
   _db.SaveChanges();
}

This works fine. However, I want to change two things

1) Can I skip the loading of the row from DB first? i.e. this line USER UserObj = _db.USERs.First(i => i.USER_ID == user.USER_ID);

2) If there are 20 fields to update, how can I set all of them at once? Or I’ll have to write all 20 assignments myself?

Thanks

Answer 1

Edit – samples modified for EFv1 – it answers both your questions:

You are looking for this:

private void SaveUser(User user)
{
    // Attach dummy entity - it must have only primary key property and EntityKey 
    // property assigned
    _db.USERs.Attach(new User() { ... });
    // Apply current values to dummy entity - this will mark the entity as modified
    // and it will also mark all properties (except key and store generated) as modified
    _db.ApplyPropertyChanges("UserSetName", user);
    _db.SaveChanges();
}

There is some difference between EntityObjects (today mostly obsolete) and POCOs (only EFv4) where POCO simply updates if it is marked as modified but EntityObject doesn’t. It will update only if properties differ to its original state or if property is manually set as modified in ObjectStateEntry.

Selectively defining which properties must be updated is the same as manually assigning them:

private void SaveUser(User user)
{
    _db.USERs.Attach(user);
    ObjectStateEntry entry = _db.ObjectStateManager.GetObjectStateEntry(user);
    entry.SetModifiedProperty("PropertyName");
    // set other properties
    _db.SaveChanges();
}

Btw. have you heard about naming conventions?