如何改进有关EntityCollections<TEntity>的这段代码？

Question

这就是我不相信的密码。请检查我是如何作为参数传递实体集合的。

public ExamProduced GetExamProduced(XElement xml)
{
    var examProduced = new ExamProduced
    {
        ExamProducedID = (int)xml.Attribute("ExamID"),
        Date = (DateTime)xml.Attribute("Date"),
        Seed = (int)xml.Attribute("Seed"),
        //Exercises = GetExercises(xml)
    };

    GetExercises(xml, examProduced.Exercises);
    return examProduced;
}

public void GetExercises(XElement xml, EntityCollection<Exercise> entityCollection)
{
    var objs =
        from objective in xml.Descendants("Objective")
        where (bool)objective.Attribute("Produced")
        let id = (int)objective.Attribute("ID")
        let id2 = (Objective)entityService.Objectives.Where(o => o.ObjectiveID == id).FirstOrDefault()
        select new Exercise
        {
            Objective = id2,
            MakeUp = ...
            Quantify = ...
            Score = ...
        };

    foreach (var exercise in objs)
    {
        entityCollection.Add(exercise);
    }
}

如果没有，我会收到一个错误。就像这个密码一样。

public ExamProduced GetExamProduced(XElement xml) 
{ 
    var examProduced = new ExamProduced 
    { 
        ExamProducedID = (int)xml.Attribute("ExamID"), 
        Date = (DateTime)xml.Attribute("Date"), 
        Seed = (int)xml.Attribute("Seed"), 
        Exercises = GetExercises(xml) 
    }; 

    return examProduced; 
} 

public EntityCollection<Exercise> GetExercises(XElement xml) 
{ 
    var objs = 
        from objective in xml.Descendants("Objective") 
        where (bool)objective.Attribute("Produced") 
        let id = (int)objective.Attribute("ID") 
        select new Exercise 
        { 
            ExerciseID = id, 
            MakeUp = (bool)objective.Attribute("MakeUp"), 
            Quantify = (byte)(int)objective.Attribute("Quantify"), 
            Score = (float)objective.Elements().Last().Attribute("Result") 
        }; 

        var entityCollection = new EntityCollection<Exercise>();

        foreach (var exercise in objs)
            entityCollection.Add(exercise);

        return entityCollection;
} 

​

​

我得到的错误如下：

InvalidOperationException没有被处理。

无法将对象添加到EntityCollection或EntityReference中。附加到ObjectContext的对象不能添加到不与源对象关联的EntityCollection或EntityReference中。

Answer 1

我希望我对你的理解是正确的.如果没有，我会更新这个答案。

首先，您的EntityCollection<Exercise> GetExercises(XElement xml)将无法工作。正如错误消息所述，您不能构建这样的随机EntityCollection：EntityCollection需要将对象附加到上下文，因为它会自动同步其列表和上下文。既然你没有说要把它附加到任何地方，它就没用了。使其工作的唯一方法是首先避免创建EntityCollection。

你的void GetExercises(XElement xml, EntityCollection<Exercise> entityCollection)程序可以工作。但是，您需要确保实际上有一个--一个EntityCollection<Exercise>实例，以便能够调用它。按照创建ExamProduced对象的方式，在您从GetExamProduced返回时它不会附加到上下文中，因此不可能在此时为它设置一个EntityCollection<Exercise>属性。

也许最简单的方法是将上下文传递给GetExamProduced方法，并让它们自动地附加到上下文中。我假设它是一个常见的ObjectContext，但是您可以根据需要更新它：

public ExamProduced GetExamProduced(XElement xml, YourContext context)
{
    var examProduced = new ExamProduced()
    {
        ExamProducedID = (int)xml.Attribute("ExamID"),
        Date = (DateTime)xml.Attribute("Date"),
        Seed = (int)xml.Attribute("Seed")
    };
    context.ExamsProduced.Attach(examProduced);
    LoadExercises(xml, context, examProduced);
    // examProduced.Exercises should be available at this point
    return examProduced;
}

public void LoadExercises(XElement xml, YourContext context, ExamProduced examProduced)
{
    foreach (var exercise in
        from objective in xml.Descendants("Objective")
        where (bool)objective.Attribute("Produced")
        let id = (int)objective.Attribute("ID")
        let id2 = (Objective)entityService.Objectives.Where(o => o.ObjectiveID == id).FirstOrDefault()
        select new Exercise
        {
            ExamProduced = examProduced,
            Objective = id2,
            MakeUp = ...
            Quantify = ...
            Score = ...
        }))
    {
        context.Exercises.Attach(exercise);
    }
}

我不知道这些对象是否应该添加到数据库中，或者这些对象是否已经存在于数据库中。我假设是后者。如果是前者，则应该在两个地方将.Attach更新为.AddObject。

这就是你要找的，还是我误会了？