c# - LINQ TO ENTITY 无法与枚举类型进行比较

Question

下面是枚举叶子

public enum Leaves
{
    Annual = 0,
    Medical = 1,
    Hospitalization = 2,
    Unpaid = 3
}

下面是linq查询

public ActionResult ApproveLeave(int? id)
    {
        if (id == null)
            return View();

        LeaveApplication leaveApplication = db.LeaveApplication.Find(id);

        if (leaveApplication == null)
            return HttpNotFound();

        leaveApplication.Status = "Approved";

        if (ModelState.IsValid)
        {
            db.Entry(leaveApplication).State = EntityState.Modified;

            Leaves leavesType = (Leaves)Enum.Parse(typeof(Leaves), leaveApplication.LeaveType.ToString());

            var lb = (from t in db.LeaveBalance
                      select t)
                      .Where(t => t.LeaveType == leavesType && t.Profileid.Equals(id))
                      .FirstOrDefault();

            lb.Taken++;
            lb.Balance--;
            db.SaveChanges();

            return RedirectToAction("Index");
        }

        return View();
    }

我什至尝试过使用 Leaves.Annual，但它不起作用。LINQ 查询抛出以下异常:

System.NotSupportedException HResult=0x80131515 Message=Unable to create a constant value of type 'System.Object'. Only primitive types or enumeration types are supported in this context.

Answer 1

Equals 在 Linq2ToEntity 中不受支持，您应该改用双等号:

var lb = (from t in db.LeaveBalance select t)
  .Where(t => t.LeaveType == leavesType && t.Profileid == id)
  .FirstOrDefault();

假设您的 Profileid 是一个整数，使用 == 应该可以在不改变逻辑或遇到大小写问题的情况下使其正常工作。