visual-studio-2010 - 被 "The EntityCollection has already been initialized."错误卡住

Question

工具:视觉工作室 2010
语言: C#

我刚刚开始学习 Entity Framework ，我遇到了一个问题，每当我使用 Code#1 时它都可以正常工作，但是每当我使用 CODE#2 时，我都会出错(发布在下面)

Title: InvalidOperationException was unhandled by user code
Error Message "The EntityCollection has already been initialized. The InitializeRelatedCollection method should only be called to initialize a new EntityCollection during deserialization of an object graph."

//SchoolModel.Designer.cs
public EntityCollection<Course> Courses
{
    get
    {  //Blah blah code }
    set
    {
        if ((value != null))
        {//Below statement is pointed by Visual Studio as Exception Thrower
            ((IEntityWithRelationships)this).RelationshipManager.InitializeRelatedCollection<Course>("SchoolModel.CourseInstructor", "Course", value);
        }
    }
}

代码# 1:

List<string> list = new List<string>();
var prs = new Person();
using (var myEntity = new SchoolEntities())
{
    var result = myEntity.People;
    foreach (var ppl in result)
    {
        list.Add(ppl.PersonID+","+ppl.FirstMidName);
    }
}

代码# 2:

List<string> list = new List<string>();
List<Person> prsList = new List<Person>();//when using this list,problem started
var prs = new Person();
using (var myEntity = new SchoolEntities())
{
    var result = myEntity.People;
    foreach (var ppl in result)
    {
        list.Add(ppl.PersonID+","+ppl.FirstMidName);

        //New code which raised exceptions
        prs.PersonID = ppl.PersonID;
        prs.FirstMidName = ppl.FirstMidName;
        prs.LastName = ppl.LastName;
        prs.Courses = ppl.Courses;
        prsList.Add(prs);
        //New code end
    }
}

数据库图:


实体图:


附注:

我在 http://www.asp.net/web-forms/tutorials/getting-started-with-ef/the-entity-framework-and-aspnet-getting-started-part-3 上关注了 EF 教程，然后偏离并开始玩它:)

我确实找到了一些相关的错误问题，但我的情况不同。

Answer 1

您不应该像在 prs.Courses = ppl.Courses 中那样设置 EntityCollection .该集合已被初始化(根据异常(exception)情况)。您只能通过 Add 修改它ing Course实例。