Can I combine a LINQ and a foreach that I use to add objects to a collection?

Question

I am using the following code:

IEnumerable<ObjectiveDetail> toBeAdded = 
   objectiveDetail1.Where(a => objectiveDetail2.All(
                          b => b.ObjectiveDetailId != a.ObjectiveDetailId));

Then:

foreach (var _obj in toBeAdded)
{
   _uow.ObjectiveDetails.Add(_obj);
}

This works and adds the one (or many) new object details to the collection.

However I am wondering. Is there another way that I could do this that would combine the LINQ and the foreach?

Answer 1

So you actually want to add all objects which are not in the second collection. Enumerable.Except is much more efficient(assuming the ObjectiveDetailId is unique):

IEnumerable<ObjectiveDetail> toBeAdded = objectiveDetail1.Except(objectiveDetail2);

You need to override Equals + GetHashCode :

public class ObjectiveDetail
{
    public int ObjectiveDetailId { get; set; }
    // other properties ...

    public override bool Equals(object obj)
    {
        var obj2 = obj as ObjectiveDetail;
        if (obj2 == null) return false;
        return ObjectiveDetailId == obj2.ObjectiveDetailId;
    }
    public override int GetHashCode()
    {
        return ObjectiveDetailId;
    }
}

Btw, you don't need the foreach , you can use AddRange :

_uow.ObjectiveDetails.AddRange(toBeAdded);

Answer 2

Yeah you can do this way -

objectiveDetail1.Where(a => objectiveDetail2.All(
                       b => b.ObjectiveDetailId != a.ObjectiveDetailId))
                      .ToList().ForEach(_uow.ObjectiveDetails.Add);

Answer 3

最短的方法是

_uow.ObjectiveDetails.AddRange(toBeAdded);

Answer 4

Yep.

_uow.ObjectiveDetails.AddRange(
    objectiveDetail1.Where(a => objectiveDetail2.All(
        b => b.ObjectiveDetailId != a.ObjectiveDetailId)));