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.

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;
}