c# - 我可以将用于将对象添加到集合中的 LINQ 和 foreach 结合起来吗？

Question

我正在使用以下代码：

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

然后：

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

这有效并将一个（或多个）新对象详细信息添加到集合中。

不过我想知道。还有另一种方法可以结合LINQ和foreach吗？

Answer 1

因此，您实际上想要添加不在第二个集合中的所有对象。Enumerable.Except效率更高（假设ObjectiveDetailId是唯一的）：

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

您需要覆盖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;
    }
}

顺便说一句，你不需要foreach，你可以使用 AddRange：

_uow.ObjectiveDetails.AddRange(toBeAdded);

Answer 2

是的，你可以这样做 -

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

是的。

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