How would you write an Upsert for LINQ to SQL?

Question

So I\'d like to write a generic Upsert function for LINQ to SQL and I\'m having some trouble conceptualizing how to do it. I\'d like it to work something like this:

Answer 1

I do something similar, but with a different approach. Every entity implements IEntity. One of the properties of IEntity is a state if the object is new or existing. I then implement that for each entity, like:

public EntityState EntityState
{
    get
    {
        if (_Id > 0)
            return EntityState.Exisiting;
        else
            return EntityState.New;
    }
}

Then, a generic Upsert could be (on a generic repository type class):

public virtual void Upsert(Ta entity)
    where Ta: class
{
    if (!(entity is IEntity))
        throw new Exception("T must be of type IEntity");

    if (((IEntity)entity).EntityState == EntityState.Exisiting)
        GetTable().Attach(entity, true);
    else
        GetTable().InsertOnSubmit(entity);
}

private System.Data.Linq.Table GetTable()
    where Ta: class
{
    return _dataContext.Context.GetTable();
}

If your attaching from another datacontext, also make sure you have a timestamp on your objects.