在实体框架中使用AttachTo不起作用

Question

I have a generic CRUD repository that attaches an updated object to the ObjectContext using AttachTo as below:

NB the property entitySetName supplies the name of the table the object is being attached to

    public virtual void Save(TModel t)
    {
            TModel unboxed = (TModel)t;
            db.AttachTo(entitySetName, unboxed);
            db.SaveChanges();
    }

No errors show up, just doesnt save the data. Can anyone see why?

Answer 1

AttachTo adds an entity to the context in state Unchanged . When you call SaveChanges immediately after that nothing gets updated because - from EF perspective - the entity is "unchanged".

You need to set the state to Modified to tell EF that properties have changed and should be written to the database:

public virtual void Save(TModel t)
{
        TModel unboxed = (TModel)t;
        db.AttachTo(entitySetName, unboxed);
        db.ObjectStateManager.ChangeObjectState(unboxed, EntityState.Modified);
        db.SaveChanges();
}

Answer 2

I believe you want to modify by a single column. You can try the .Attach .

    public virtual void Save(TModel t)
    {
        db.SystemUserLogs.Attach(t);
        //db.Entry(t).State = EntityState.Modified; //<--- For whole fields modifier

        db.Entry(t).Property(x => x.entitySetName).IsModified = true; //<--- For one field modifier
        db.SaveChanges();
    }