Question

我有一个看起来像这样的函数：

public UpdateRecord(MyObjectModel TheObject, int TheUserID)
{
  using (MyDataContextModel TheDC = new MyDataContextModel())
  {
     var TheObjectInDB = (from o in TheDC.TheObjects
                          where o.ObjectID == TheObject.ObjectID
                          select new MyObjectModel()).SingleOrDefault();

     if (TheObject.Prop1 != null) { TheObjectInDB.Prop1 = TheObject.Prop1; }
     if (TheObject.Prop2 != null) { TheObjectInDB.Prop2 = TheObject.Prop2; }

     TheDC.SubmitChanges();
  }
}

代码没有崩溃，但它没有更新数据库。我需要改变什么？

Answer 1

选择o而不是新的MyObjectMode（），修改：

var TheObjectInDB = (from o in TheDC.TheObjects
                          where o.ObjectID == TheObject.ObjectID
                          select o).SingleOrDefault();

Answer 2

首先，在查询中执行select new MyObjectModel()，这将始终创建一个新对象，关注从数据库中提取的内容。将其更改为select o。

其次，在：

if (TheObject.Prop1 != null) { TheObjectInDB.Prop1 = TheObject.Prop1; }
if (TheObject.Prop2 != null) { TheObjectInDB.Prop2 = TheObject.Prop2; }

有条件地更新对象的值。因此，如果Prop1和Prop2为空，则不会更新对象的属性。

Answer 3

以下代码有效，与您发布的内容几乎相同。

DataContext dc = new DataContext(ConnectionString);
var q = from a in dc.GetTable<Employee>()
        where a.EmployeeID == this.EmployeeID
        select a;
Employee temp = q.Single<Employee>();
temp.EmployeeActiveStatus = this.EmployeeActiveStatus;
temp.EmployeeName = this.EmployeeName;
temp.EmployeeUserID = this.EmployeeUserID;
temp.EmployeeCreateModifyDate = this.EmployeeCreateModifyDate;
temp.EmployeePaperWork = this.EmployeePaperWork;
dc.SubmitChanges();

我看到的唯一主要区别是这条线：选择新的MyObjectMode（））。SingleOrDefault（）

在c＃中使用linq更新数据库记录到sql

3 个答案: