Json into EF with duplicates-CodePudding

I have following sample JSON (simplified):

{
   "programmes":[
      {
             "programmeID":"163",
             "title":"Programme 1",
             "color":"#ff5f57",
             "moderators":[
                {
                   "moderatorID":"27",
                   "name":"Moderator 1",
                }
             ]
          },
          {
             "programmeID":"153",
             "title":"Programme 2",
             "color":"#ff5f57",
             "moderators":[
                {
                   "moderatorID":"27",
                   "name":"Moderator 1",
                }
             ]
          },

       ]
}

I want to convert into following objects:

    public class Programme
    {
        [Key]
        public string programmeID { get; set; }
        public string title { get; set; }

        //Navigational Property
        public virtual ICollection<Moderator> moderators { get; set; }
    }

    public class Moderator
    {
        [Key]
        public string moderatorID { get; set; }
        public string name { get; set; }

        //Navigational Property
        public virtual ICollection<Programme> programmes { get; set; }
    }

Everything is fine, objects looks great, populated correctly, but when trying to save into db a get this error:

The instance of entity type 'Moderator' cannot be tracked because another instance with the key value '{moderatorID: 27}' is already being tracked. When attaching existing entities, ensure that only one entity instance with a given key value is attached.

This error happens when calling .Add with the list of Programmes:

List<Programme> programmes;
programmes = JsonSerializer.Deserialize<List<Programme>>(JSONcontent);
//... db init
db.AddRange(programmes);

I understand that there is a duplicity for Moderator (ID=27), but I think that it's quite a normal pattern in JSON. I can do some workaround, but wondering if there is any best practice how to handle this in EF directly?

CodePudding user response：

you can not add children you are created from deserialization as an existed ones. One of the solutions is finding the existed children at first

List<Programme> programmes = JsonSerializer.Deserialize<List<Programme>>(JSONcontent);

foreach (var program in programmes)
{
var moderators=new List<Moderator>();
foreach (var moderator in program.moderators)
{
     var existingModerator=db.Moderators.FirstOrDefault(i=> 
                 i.moderatorId=moderator.moderatorId);
    moderators.Add(existingModerator);
}
  programm.moderators=moderators;
}
db.AddRange(programmes);

but I usually prefer to create an explicit class for many to many relations. It will make all your code much more simple.