實體框架上下文問題

Question

好吧...實體框架6問題的所有y'alls。

我在寫一個使用EF的小型Intranet門戶。這是一個非常簡單的使用gridview的CRUD。 Everthings要游泳，但我在嘗試保存更改時遇到問題。

爲了在gridview上進行分頁，排序和過濾，我創建了一個包含實體對象列表的會話變量，然後將該會話變量綁定到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(); 
} 

這樣，如果用戶過濾列表中上下設置更小的結果或排序和網頁，然後做觸發回發一些其他的事件，GridView的設置保持不變。

但從我所知道的，會話[「vlans」]中的Vlans列表不再有上下文（由於回發事件？）。所以當我嘗試編輯選定的vlan並保存它（特別是當我嘗試將一個environment_type子實體添加到vlan實體時），我收到一個錯誤。

我已經嘗試將vlan條目重新連接到_context中，但是它帶來了一個「蠟燭球」。做這個的最好方式是什麼？

這裏是我的更新，因爲它代表：

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

你_context創建您發表或讓每一個時間，和VLAN的列表被綁定到不同的環境作爲一個結果。

會話不關心POST或GET，我想你應該改變這樣的：

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

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

要這樣：

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(); 
}