LINQ问题：从数据库读取对象，出现异常

Question

我对LINQ相当陌生，而且我遇到了一些问题。我尝试了一段时间的谷歌搜索，但我仍然没有找到任何精确的答案来解决我的问题，所以我也会问。

我已经在Microsoft SQL Server上建立了一个测试数据库，其中有两个表“Person2”和“Department2”。 Person2与Department2有多对一的关系。许多人只属于一个部门。

PERSON2具有以下属性：

• ID（INT，主键）
• 名称（NCHAR（50））
• phoneNumber的（NCHAR（10））
• DepartmentID的（INT，外国主要用名： “fk_Department2_DepartmentID”）

Department2具有以下属性：

• DepartmentID的（INT，主键）
• DepartmentDesc（NCHAR（50））

的C＃-code由四个班的两个项目文件：人，部和方案（运行测试），另一个是TabellTest。 这是我试图运行代码：

using System; 
using System.Collections.Generic; 
using System.Linq; 
using System.Text; 
using System.Threading.Tasks; 
using System.Data.Linq; 
using System.Data.Linq.Mapping; 

namespace DBTest 
{ 
    [Database] 
    public class TableTest : DataContext 
    { 
     public Table<Person> persons; 
     public Table<Department> departments; 

     public TabellTest(String ConnectionString): 
      base(ConnectionString){} 

    } 

} 


using System; 
using System.Collections; 
using System.Linq; 
using System.Text; 
using System.Threading.Tasks; 
using System.ComponentModel; 
using System.Data; 
using System.Drawing; 
using System.Data.Linq; 
using System.Data.Linq.Mapping; 

namespace DBTest 
{ 
    [Table(Name = "Person2")] 
    public class Person 
    { 

     public Person() { } 

     [Column(IsPrimaryKey = true)] 
     private int id; 
     public int Id 
     { 
      get { return this.id; } 
      set { this.id = value; } 
     } 

     [Column] 
     private string name; 
     public string Name 
     { 
      get { return this.name; } 
      set { this.name = value; } 
     } 

     [Column] 
     private string phoneNumber; 
     public string PhoneNumber 
     { 
      get { return this.phoneNumber;} 
      set { this.phoneNumber = value;} 
     } 

     [Column (Name="DepartmentID")] 
     private int? personDepartmentID; 
     public int? PersonDepartmentID 
     { 
      get { return this.personDepartmentID; } 
      set { this.personDepartmentID = value; } 
     } 

     [Association(Name = "FK_Person_PersonDepartment", 
     IsForeignKey = true, Storage = "_department", ThisKey = "personDepartmentID")] 
     private EntityRef<Department> _department; 
     public Department Department 
     { 
      get { return _department.Entity; } 
      set { _department.Entity = value; } 
     } 



    } 

    [Table (Name = "Department2")] 
    public class Department { 

     public Department() { } 

     public Department(int departmentID, string departmentDesc) 
     { 
      this.departmentID = deparmentID; 
      this.departmentDesc = departmentDesc; 
     } 

     [Column(IsPrimaryKey = true)] 
     private int departmentID; 
     public int DepartmentID 
     { 
      get {return this.departmentID; } 
      set {this.departmentID = value; } 
     } 

     [Column] 
     private string departmentDesc; 
     public string DepartmentDesc 
     { 
      get { return this.departmentDesc; } 
      set { this.departmentDesc = value; } 
     } 

     private EntitySet<Person> _person = new EntitySet<Person>(); 
     [Association(Name = "FK_Person_PersonDepartment", 
     IsForeignKey = true, Storage = "_person", ThisKey = "departmentID", OtherKey="personDepartmentID")] 
     public EntitySet<Person> person 
     { 
      get { return _person; } 
      set { _person = value; } 
     } 


    } 

    class Program 
    { 
     static void Main(string[] args) 
     { 
      TableTest Test = new TableTest("REMOVED FOR STACKOVERFLOW.COM, JUST ASSUME IT WORKS"); 

      foreach (Person pers in Test.persons) 
      { 
       Console.WriteLine(pers.Name + " " + pers.Id + " " + pers.PhoneNumber + " " + pers.Department.DepartmentID + " " + pers.Department.DepartmentDesc); 
      } 

      Console.WriteLine("\n\n"); 
      foreach (Department dep in Test.department) 
      { 
       Console.WriteLine(dep.DepartmentID + " " + dep.DepartmentDesc); 
       foreach (Person pers in dep.person) 
       { 
        Console.WriteLine(pers.Name + " " + pers.Id + " " + pers.PhoneNumber); 
       } 
      } 

     } 
    } 
} 

问题的核心是该代码段中的类人：

[Association(Name = "FK_Person_PersonDepartment", IsForeignKey = true, 
    Storage = "_department", ThisKey = "personDepartmentID")] 
    private EntityRef<Department> _department; 
    public Department Department 
    { 
     get { return _department.Entity; } 
     set { _department.Entity = value; } 
    } 

每当我试着运行该程序，我得到此例外：

未处理的异常：System.InvalidOperationException：ThisKey列的数量与'Person'类型中关联属性'_department'的OtherKey列的数量不同 在.......等等等等等等

的溶液使用Google问题建议我的OtherKey属性添加到关联，在这种情况下，该协会代码变成这样，当我发现：

[Association(Name = "FK_Person_PersonDepartment", IsForeignKey = true, 
Storage = "_department", ThisKey = "personDepartmentID", OtherKey = "departmentID")] 

（我也试图与资本d：OtherKey = “DepartmentID的”）

当我这样做，我得到这个异常：

未处理的异常：System.InvalidOperationException：找不到类型为'EntityRef 1´. The key may be wrong or the field or property on ´EntityRef 1'的关键'departmentID'的关键成员'departmentID'已更改名称。 在....等等等等

具有讽刺意味的是，该协会段自处，这与EntitySet的操作同时使用的按键（只接通ThisKey和OtherKey），和作品。 换句话说：我无法从Person类的数据库中获取Department对象，但它可以在Department-Code中获取Person对象的集合。

现在，亲爱的读者和程序员，你建议我做什么？

Answer 1

看起来它可能只是订单 - 您正在修改私人会员而非公众;你试过这个吗？

private EntityRef<Department> _department; 
[Association(Name = "FK_Person_PersonDepartment", IsForeignKey = true, 
    Storage = "_department", ThisKey = "personDepartmentID", OtherKey = "departmentID")] 
public Department Department 
{ 
    get { return _department.Entity; } 
    set { _department.Entity = value; } 
}