c# - 无法转换类型为 'System.Data.Objects.MaterializedDataRecord' 的对象

Question

我有一个与 EntityDataSource 相连的 GridView。

EntityDataSource 有一个 Where Parameters 的内部参数。到目前为止一切正常。

    <asp:EntityDataSource ID="EntityDataSourceListAuthors" runat="server" ConnectionString="name=CmsConnectionStringEntityDataModel"
        DefaultContainerName="CmsConnectionStringEntityDataModel" EnableFlattening="False"
        EntitySetName="CmsAuthors" EntityTypeFilter="" OrderBy="it.FirstName" Select="it.AuthorId, it.UserId, it.FirstName, it.LastName, it.NoteInternal, it.ContentAuthor"
        Where="it.UserId = @ActiveUser">
    </asp:EntityDataSource>

---

我使用 Event RowDataBound 和 Entity Framework 来检索每一行的值并执行一些逻辑。

我一运行代码就收到这个错误:

Unable to cast object of type 'System.Data.Objects.MaterializedDataRecord' to type 'WebProject.DataAccess.DatabaseModels.CmsAuthor'.

在我看来，向 EntityDataSource 添加参数时 smt 发生了变化，因此我无法像以前那样使用 EF 任何想法？谢谢大家!

---

        protected void uxListAuthorsDisplayer_RowDataBound(object sender, GridViewRowEventArgs e)
    {
            switch (e.Row.RowType)
            {
                // In case type of row is DataRow (a data row of GridView) 
                case DataControlRowType.DataRow:
                    // Display friendly User's Name instead of his Guid
                    // Retrive underlying data from a single row rappresented in GridView (use Entity Framwork)                
                    WebProject.DataAccess.DatabaseModels.CmsAuthor myRow = (WebProject.DataAccess.DatabaseModels.CmsAuthor)e.Row.DataItem;
                    // Retrive the Guid for a User in a specific row
                    Guid myUserGuid = (Guid)myRow.UserId;
                    // Find out used UserName using Guid UserId
                    MembershipUser mySelectedUser = Membership.GetUser(myUserGuid);
                    // Write friendly User's Name instead of his Guid value in a specific Grid View Cell
                    e.Row.Cells[3].Text = mySelectedUser.UserName;

                    // Disable Delete Button if a Content has associated an Author
                    // Use Entity Framwork for retriving data - Create a "Context" for a single Row
                    using (CmsConnectionStringEntityDataModel context = new CmsConnectionStringEntityDataModel())
                    {
                        // Find out Row Id and create an varaible to store it
                        int myWorkingRowId = myRow.AuthorId;
                        // Find the Edit Link
                        HyperLink myEditLink = (HyperLink)e.Row.FindControl("uxLinkEditButton");
                        // Find the Delete Button
                        LinkButton myDeleteButton = (LinkButton)e.Row.FindControl("uxLinkDeleteButton");
                        // Find the System Note Label
                        Label mySystemNote = (Label)e.Row.FindControl("uxSystemNoteDisplayer");
                        // Use of Lamba Espression with EF to check if an Author is associated with a Content
                        CmsContent authorIdInContent = context.CmsContents.FirstOrDefault(x => x.AuthorId == myWorkingRowId);
                        // Make visible or invisible the Delete Button if an Author is associated to a Content
                        if (authorIdInContent != null)
                        {
                            myDeleteButton.Visible = false;
                            mySystemNote.Text = "Author is being used in Contents";
                        }
                        else
                        {
                            myDeleteButton.Visible = true;
                        }

                        // Programmatically Limiting Functionality depending on User's Roles
                        myEditLink.Visible = User.IsInRole("CMS-ADMINISTRATOR") || User.IsInRole("CMS-AUTHOR") || User.IsInRole("CMS-EDITOR");
                        myDeleteButton.Visible = User.IsInRole("CMS-ADMINISTRATOR");
                    }
                    break;
            }
        }

Answer 1

阅读 Diego Vega 关于在 RowDataBound 事件中绑定(bind) EntityDataSource 的博文:

http://blogs.msdn.com/b/diego/archive/2008/05/13/entitydatasource-to-wrap-or-not-to-wrap.aspx

你遇到了他的“包装规则”的第四个场景。

Finally, if you set the Select property to do a projection (i.e. "it.CustomerID, it.CustomerName", you get DbDataRecord regardless of how you start your query.

您将无法获取源实体。您必须将 DataItem 视为 DataRow 之类的东西。

If e.Row.RowType = DataControlRowType.DataRow Then

    Dim rowCmsAuthor = CType(e.Row.DataItem, Data.Common.DbDataRecord)

    Dim myUserID As Integer = rowCmsAuthor("UserId")

End If

或者，您可以从 EntityDataSource 中删除 Select 属性。尝试使用 Diego 规则的场景 1 或场景 2 进行包装。