Insert element into nested array in Mongodb

Question

I have this :

{
  "_id" : ObjectId("4fb4fd04b748611ca8da0d48"),
  "Name" : "Categories",
  "categories" : [{
      "_id" : ObjectId("4fb4fd04b748611ca8da0d46"),
      "name" : "SubCategory",
      "sub-categories" : [{
          "_id" : ObjectId("4fb4fd04b748611ca8da0d47"),
          "name" : "SubSubCategory",
          "standards" : []
        }]
    }]
}

I would like to add a new SubCategory using the C# driver. Is there an optimal way to do this?

Answer 1

You can do this using FindOneAndUpdateAsync and positional operator

public async Task Add(string productId, string categoryId, SubCategory newSubCategory)
{
    var filter = Builders<Product>.Filter.And(
         Builders<Product>.Filter.Where(x => x.Id == productId), 
         Builders<Product>.Filter.Eq("Categories.Id", categoryId));
    var update = Builders<Product>.Update.Push("Categories.$.SubCategories", newSubCategory);
    await collection.FindOneAndUpdateAsync(filter, update);
}

Answer 2

You can use the positional operator using Linq expressions too:

public async Task Add(string productId, string categoryId, SubCategory newSubCategory)
{
    var filter = Builders<Product>.Filter.And(
         Builders<Product>.Filter.Where(x => x.Id == productId), 
         Builders<Product>.Filter.ElemMatch(x => x.Categories, c => c.Id == categoryId));
    var update = Builders<Product>.Update.Push(x => x.Categories[-1].SubCategories, newSubCategory);
    await collection.FindOneAndUpdateAsync(filter, update);
}

And get yourself free of using hard-coded property names inside strings.

Answer 3

Adding an example for my case. Did work but without the dollar sign when entering inside an array:

public async Task AddCustomMetadata()
       {
            Dictionary<string, string> dic = new Dictionary<string, string>();
            dic.Add("EntityCustomMetadataFieldId", "5bf81296-feda-6447-b45a-08d5cb91211c");
            var filter = Builders<BsonDocument>.Filter.Eq("_id", "6c7bb4a5-d7cc-4a8d-aa92-b0c89ea0f7fe");
            var update = Builders<BsonDocument>.Update.Push("CustomMetadata.Fields", dic);
            await _context.BsonAssets.FindOneAndUpdateAsync(filter, update);
        }