实体框架上下文问题

Question

好吧...实体框架6的所有问题。

我正在使用EF编写一个小型的Intranet门户。 这是一个使用gridview的非常简单的CRUD。 一切都很顺利，但尝试保存更改时遇到问题。

为了在gridview上进行分页，排序和过滤，我创建了一个包含实体对象列表的会话变量，然后将该会话变量绑定到gridview。

//Class level variables
private nsdc_supplyEntities _context = new nsdc_supplyEntities();
private VlanClass _vc;
private EnvironmentTypesClass _ec;

protected void Page_Load(object sender, EventArgs e)
{
    _vc = new VlanClass(_context);
    _ec = new EnvironmentTypesClass(_context);

    if (!IsPostBack)
    {
        Session["vlans"] = _vc.GetAllVlans();
        BindData();
    }
}

protected void BindData()
{
    GridView1.DataSource = Session["vlans"];
    GridView1.DataBind();
}

protected void GridView1_EditVlan(object sender, GridViewEditEventArgs e)
{
    GridView1.EditIndex = e.NewEditIndex;
    BindData();
}

这样，如果用户将列表过滤到较小的结果集或进行排序和页面排序，然后执行触发回发的其他事件，则Gridview的集合将保持不变。

但是据我所知，Session [“ vlans”]中的VLAN列表不再具有上下文（由于回发事件？）。 因此，当我尝试编辑所选vlan并将其保存时（尤其是当我尝试将vlane_type子实体添加到vlan实体时），我会收到错误消息。

我尝试过将vlan条目重新附加到_context中，但这带来了整个“另一个蜡球”。 做这个的最好方式是什么？

这是我目前的更新：

protected void UpdateVlan(object sender, GridViewUpdateEventArgs e)
{
    CheckBoxList environmenttypesCBL = (GridView1.Rows[e.RowIndex].FindControl("EnvironmenttypesCBL") as CheckBoxList);
    int vlanid = Convert.ToInt32(((Label)GridView1.Rows[e.RowIndex].FindControl("lblid")).Text);

    //At first I was creating a new instance of vlan in question and saving that, 
    //but then database and the Session["vlan"] variable (and gridview) is out of sync
    //vlan editedVlan = new vlan();
    //editedVlan = _vc.GetVlanByID(vlanid);

    //Get the vlan I am editing from Session["vlan"]
    List<vlan> list = Session["vlans"] as List<vlan>;
    vlan editedVlan = list.Find(i => i.id == vlanid);

    //Tried reattaching but "The object cannot be detached because it is not attached to the ObjectStateManager."
    //_context.Attach(editedVlan);

    #region EnvironmentTypes
    editedVlan.environment_type.Clear();
    if (environmenttypesCBL.Items.Count > 0)
    {
        foreach (ListItem l in environmenttypesCBL.Items.Cast<ListItem>())
        {
            //tried adding an environment_type to the editedVlan but "The object cannot be detached because it is not attached to the ObjectStateManager."
            if (l.Selected)
                editedVlan.environment_type.Add(_ec.GetEnvironmentTypeByID(Convert.ToInt32(l.Value)));
        }
    }
    #endregion

    _vc.UpdateSelectedVlan();

    GridView1.EditIndex = -1;
    BindData();
}

Answer 1

每次POST或GET都会创建_context，因此，VLAN列表将绑定到不同的上下文。

会话不关心POST或GET，我认为您应该更改此设置：

_vc = new VlanClass(_context);
_ec = new EnvironmentTypesClass(_context);

if (!IsPostBack)
{
    Session["vlans"] = _vc.GetAllVlans();
    BindData();
}

对此：

if (Session["vlans"] == null )
{
   _context = new nsdc_supplyEntities();  // only create the context here not in the instance var declaration.
   _vc = new VlanClass(_context);
   _ec = new EnvironmentTypesClass(_context);
    Session["vc"] = _vc;
    Session["vlans"] = _vc.GetAllVlans();
    Session["context"] = _context;
}
else
{
    _context = (DbContext)Session["context"];  // cast to your Context
   _vc = (VlanClass) Session["vc"]  ;
}

if (!IsPostBack)
{
    BindData();
}