Question

I have a document with sub-documents and sub-sub-documents

{
 "ClockID" : "fd51b6e0-5b81-49ab-8424-71fd768281b2",
 "ClockName" : "AAA-TEST123-002",
 "FilesList" : [{
                 "FileName" : "AAA-TEST123-002.mpg",
                 "FileLocationHistory" :    [{
                                               "FullPath" : "192.168.32.166/Ingestion",
                                               "AllowDeleteOnCancel" : false,
                                               "_id" : "565b7343-9dc5-4916-a788-0f392fce2502"
                                    }],
                  "_id" : "15b54499-a0be-4278-82ed-58c82c13bd40",
               }],
 "_id" : ObjectId("510164d0a63cfa2250fd6d19"),
 "_t" : "ClockRecord"

This is mapped to 3 classes:

public class ClockRecord : IDatabaseRecord
{
      public ClockRecord()
      {
         FilesList = new List<ClockRecordFile>();
      }
      public string ClockID { get; set; }
      public string ClockName { get; set; }        
      public List<ClockRecordFile> FilesList { get; set; }
      public BsonObjectId _id { get; set; }
}

public class ClockRecordFile
{
     public ClockFileRecord()
     {
         FileLocationHistory = new List<ClockFileLocationHistoryRecord>();
     }
     public string FileName { get; set; }
     public string FileStatus { get; set; }
     public string _id { get; set; }
 }

public class ClockFileLocationHistoryRecord
{
    public string FullPath { get; set; }
    public bool AllowDeleteOnCancel { get; set; }
    public string _id { get; set; }
}

And I use this method to retrieve the top level document:

public List<ClockRecord> GetClocksByID(string id)
{
   var collection = MongoDatabase.GetCollection<ClockRecord>(Collections.Clocks);
   var query = from e in collection.AsQueryable()
            where e._id == ObjectId.Parse(id) 
             select e;

   var clocks = query.ToList();
   return clocks;
}

So,
when I want to update a sub-document in the FilesList array I use this:

    public void UpdateClocksFilesRecord(string collectionName, ClockFileRecord clockFileRecord, BsonObjectId clockDocumentID)
    {
        var mongoCollection = MongoDatabase.GetCollection<ClockRecord>("Clocks");
        var update = Update.Set("FilesList.$", BsonDocumentWrapper.Create<ClockFileRecord>(clockFileRecord));
        var modeResult = mongoCollection.Update(
                Query.And(
                Query.EQ("_id", clockDocumentID),
                Query.ElemMatch("FilesList", Query.EQ("_id", clockFileRecord._id))
                ),
                update, UpdateFlags.Upsert
                );
    }

This works fine.

When I want to update a sub-sub-document in the FilesList.FileLocationHistory array I use this:

    public void UpdateClockFilesLocationRecord(string collectionName, ClockFileLocationHistoryRecord clockFileLocationHistory, BsonObjectId clockDocumentID, string clockFileDocumentID)
    {
        var mongoCollection = MongoDatabase.GetCollection<ClockRecord>("Clocks");
        var update = Update.Set("FilesList.$.FileLocationHistory", BsonDocumentWrapper.Create<ClockFileLocationHistoryRecord>(clockFileLocationHistory));
        var modeResult = mongoCollection.Update(
             Query.And(
                Query.EQ("_id", clockDocumentID),
                Query.EQ("FilesList._id", clockFileDocumentID)
                ), 
              update, UpdateFlags.Upsert
              );
    }

This updates the sub-sub-document OK but when I run GetClocksByID() to deserialise the document I get an error:

“An error occurred while deserializing the FilesList property of class ClockRecord:

An error occurred while deserializing the FileLocationHistory property of class ClockFileRecord:

Expected element name to be ‘_t’, not FullPath.”

Now the FileLocationHistory document did not have a property _t before the edit and it de-serialized just fine (the top level document does have _t).

Why is the driver expecting the document to have an _t property after the update?
And what should I do about it?

Additional:
The only change I can see is that the FileLocationHistory document changes the order of fields after the update. I don’t know if this relevant.

Answer 1

OK, the problem is that my Update code is turning FileLocationHistory from an array of documents into an object.
I have posted this as a new question:

“Why does my Update to a sub document remove the array nature of sub document”