Question

如何更新现有的LINQ实体？
这段代码告诉我：“无法插入已存在的实体。”
有关使用linq更新/插入的更好的做法吗？

     foreach (ListViewItem lvi in lvStudents.Items)
        {
            HiddenField hfStudentID = lvi.FindControl("hfID") as HiddenField;
            CheckBox cbPresent = lvi.FindControl("mycb") as CheckBox;
            int sInt = Int32.Parse(hfStudentID.Value);
            dc = new DataClassesSODataContext();//I renewed the dc to make sure that wasn't the problem?

            var currStudent = dc.students.Single(x => x.studentID == sInt);

            grade g = dc.grades.Single(x => x.subjectID == subjID || x.studentID == sInt);
            if (g == null)
            {
                g = new grade();
                g.subject = dc.subjects.Single(x => x.subjectID == subjID);
                g.student = currStudent;
                g.present = cbPresent.Checked;
                dc.grades.InsertOnSubmit(g);
            } else
            {
                g.present = cbPresent.Checked;                    
                dc.grades.Attach(g, true);//I tried both attaching and inserting
            }
        }

        dc.SubmitChanges();

Answer 1

您只需设置现有实体的值，然后调用submitchanges。类似的东西：

var g=dc.grades.Single(x => x.subjectID == subjID || x.studentID == sInt);
g.subject="some new subject";
dc.SubmitChanges();

Insert仅用于添加新实体，attach用于将实体从另一个DataContext附加到现有上下文。

如何更新现有的LINQ实体？

1 个答案: