Json into EF with duplicates

Question

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?

From what you wrote, the save appears to be trying to do an insert and not an update. — ΩmegaMan, May 09 '22 at 14:27
this might help: https://stackoverflow.com/questions/62278581/saving-deserialized-json-objects-to-database-with-duplicate-child-entities — nilsK, May 09 '22 at 14:31
simplified code added, good point that it's not update, but insert. The problem is how to handle correctly. — Tomas Svestka, May 09 '22 at 14:46
Do you want insert only programme or the 2 entity? See this link https://stackoverflow.com/questions/25441027/how-do-i-stop-entity-framework-from-trying-to-save-insert-child-objects — Den, May 09 '22 at 14:56

score 0 · Accepted Answer · answered May 09 '22 at 15:31

0

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.

answered May 09 '22 at 15:31

Serge

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What exactly do you mean by "explicit class" as many:many table is generated by EF. I can see it the database. – Tomas Svestka May 09 '22 at 16:09
@TomasSvestka You can define ProgrammeModerator class manually – Serge May 09 '22 at 16:10
I can, but please how does it resolve issue with duplicity? Is there any trick to tell EF how to process such case? – Tomas Svestka May 09 '22 at 16:20
@TomasSvestka Yes, in this case you can create ProgrammeModerator class and assign Programme and ModeratorId – Serge May 09 '22 at 16:37
And you mean, do it manually, right? that makes sense, thanks! – Tomas Svestka May 10 '22 at 04:37

Json into EF with duplicates

1 Answers1