vb.net - LINQ to SQL 定义对象标识的成员无法更改

Question

我正在为 LINQ to SQL CUD 编写通用。我

'通用插入

Public Shared Sub Add(Of T As Class)(ByVal entity As T)

    Using db As New APIUDataContext()

        db.GetTable(Of T)().InsertOnSubmit(entity)
        db.SubmitChanges()

    End Using

通用插入运行良好。

'一般更新

Public Shared Sub Update(Of T As Class)(ByVal oldEntity As T, ByVal newEntity As T)

    Dim db As New DemoDataContext()

    db.GetTable(Of T)().Attach(newEntity, oldEntity)
    db.SubmitChanges()

End Sub

'使用通用更新

    Dim oldEntity As New TestAuthor
    oldEntity.Id = 4
    oldEntity.FirstName = "James"

    Dim newEntity As New TestAuthor
    newEntity.FirstName = TextBox1.Text
    newEntity.LastName = TextBox2.Text

    GenericCUD.Update(oldEntity, newEntity)

来自通用更新的错误消息。

“TestAuthor”类型的对象的成员“Id”的值已更改。定义对象身份的成员不能更改。考虑添加具有新标识的新对象并删除现有对象。

我需要修改通用更新什么？谢谢。

Answer 1

您的 newEntity 对象的 Id 不是 4，而是 0，因此这两个对象不被视为对应于同一数据库行。

Dim newEntity As New TestAuthor
newEntity.Id = oldEntity.Id
newEntity.FirstName = TextBox1.Text
newEntity.LastName = TextBox2.Text