此上下文僅支持原始類型（“例如 Int32、String 和 Guid”）

Question

我收到以下錯誤：

無法創建類型為“Phoenix.Intranet.Web.ClientSettings.ComponentRole”的常量值。 此上下文僅支持原始類型（“例如 Int32、String 和 Guid”）。

我明白為什么會發生錯誤。 我不明白為什么我的代碼會產生錯誤。 我的比較是針對原始類型的。 所有比較都是Guid to Guid。 該錯誤特別指出Guids沒問題。

錯誤發生在這一行（朝向底部）：

 var vla =  (from cir in phoenixEntities.ComponentInRoles

代碼：

List<ComponentRole> roles;
using (IMSMembershipEntities entities = new IMSMembershipEntities())
{
    roles = (from role1 in entities.Roles
             select new ComponentRole{Name = role1.RoleName, RoleId = role1.RoleId} ).ToList();
}

List<Components> componentInRoles;

using (PhoenixEntities phoenixEntities = new PhoenixEntities())
{
    phoenixEntities.ContextOptions.LazyLoadingEnabled = false;
    componentInRoles = (from component in phoenixEntities.Components
                        select new Components{Name = component.Name,
                                              ComponentId = component.ComponentId,
                                              //InRoles = (from componentInRole in phoenixEntities.ComponentInRoles
                                              //           join role in roles on componentInRole.RoleId equals role.RoleId 
                                              //           where componentInRole.ComponentId == component.ComponentId
                                              //           select new ComponentRole{RoleId = role.RoleId, Name = role.Name})
                                              }
                       ).ToList();


    foreach (Components cmpent in componentInRoles)
    {
        Components cmpent1 = cmpent;
        //cmpent.InRoles = 

         var vla =  (from cir in phoenixEntities.ComponentInRoles
                     join role in roles on cir.RoleId equals role.RoleId
                     where cir.ComponentId == cmpent1.ComponentId
                         select role).ToList();
    }
}

Answer 1

EntityFramework and Linq to SQL both try to translate such queries which a part is in memory and the other part is in Database, to sql IN operator.

並且因為您的角色是 IEnumerable 的 class 不是原始類型，所以它不能轉換為 SQL 查詢。

您應該首先從數據庫中獲取 memory，然后加入 memory 中的兩個列表。

例如：

 var vla =  (from cir in phoenixEntities.ComponentInRoles.ToList()
                     join role in roles on cir.RoleId equals role.RoleId
                     where cir.ComponentId == cmpent1.ComponentId
                         select role).ToList();

我希望我有所幫助