在插入新的父对象时，防止EF添加新的子对象而不是关联？ [英] Prevent EF from adding new child objects instead of just association when inserting new parent object?

问题描述

我有以下内容：

  public int CreateExercise（Exercise newExercise）{
 
 db。 Exercises.Add（newExercise）; 
 db.SaveChanges（）; 
 return newExercise.ExerciseId; 
} 
  

运动如下：

  public class Exercise {
 
 public Exercise（）{
 Users = new Collection< User>（）; 
} 
 
 [Key] 
 [必需] 
 public int ExerciseId {get;组; } 
 
 [StringLength（300，ErrorMessage =该值不能超过300个字符。）] 
 public string Title {get;组; } 
 
 public virtual ICollection< User>用户{get;组; } 
} 
  

当我创建一个新的练习时，有时预先存在的用户随身携带，Id包含。即使对于这些用户指定的现有 UserId ，新的用户条目被添加到这里。我只想添加关联，而不是新用户 - 我想象，EF很聪明，可以弄清楚这一点？我究竟做错了什么？

我只是想避免必须循环遍历所有附加到新练习的用户，在添加 ing，确保它们存在，添加练习，然后添加每个用户，最后调用 SaveChanges 。

解决方案

当连接的实体重新连接时，默认情况下它们处于添加状态。

  public int CreateExercise（练习newExercise）{
 
 db.Exercises.Add（newExercise）; 
 
 //将所有附加的用户设置为不变。 
 db.ChangeTracker.Entries< User>（）。ToList（）。ForEach（p => p.State = EntityState.Unchanged）; 
 
 db.SaveChanges（）; 
 return newExercise.ExerciseId; 
} 
  

I have the following:

    public int CreateExercise(Exercise newExercise) {

        db.Exercises.Add(newExercise);
        db.SaveChanges();
        return newExercise.ExerciseId;
    }

Where Exercise is the following:

public class Exercise {

    public Exercise() {
        Users = new Collection<User>();
    } 

    [Key]
    [Required]
    public int ExerciseId { get; set; }

    [StringLength(300, ErrorMessage = "The value cannot exceed 300 characters. ")]
    public string Title { get; set; }

    public virtual ICollection<User> Users{ get; set; }
 }

When I create a new Exercise, sometimes pre-existing Users come with it, Id included. Even with an existing UserId specified for these Users, new User entries are getting added here. I only want to add associations, not new users - I'd imagine EF is smart enough to figure this out? What am I doing wrong?

I'm just trying to avoid having to loop through all Users attached to a new Exercise, clearing them out before Adding, making sure they exist, adding the exercise, and then adding each individual user, finally calling SaveChanges.

解决方案

When disconnected entities are reattached they are in Added state by default.

You can change the state after attaching the exercise.

public int CreateExercise(Exercise newExercise) {

    db.Exercises.Add(newExercise);

    // set all attached users to unchanged.
    db.ChangeTracker.Entries<User>().ToList().ForEach(p => p.State = EntityState.Unchanged);

    db.SaveChanges();
    return newExercise.ExerciseId;
}

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