public async Task <KnowledgeModel> SaveAsync(KnowledgeModel entity)
        {
            var collection = MongoClientManager.DataBase.GetCollection <KnowledgeModel>(CollectionNames.Knowledge);

            await collection.InsertOneAsync(entity as KnowledgeModel);

            Console.WriteLine("document added: " + entity.ToJson());

            var filter = new BsonDocument();

            Console.WriteLine("count:" + collection.CountDocuments(filter).ToString());


            return(entity);
        }
        public async Task <KnowledgeModel> UpdateAsync(KnowledgeModel entity)
        {
            var collection = MongoClientManager.DataBase.GetCollection <KnowledgeModel>(CollectionNames.Knowledge);


            await collection.ReplaceOneAsync(d => d.ID == entity.ID, entity);

            Console.WriteLine("document updated: " + entity.ToJson());

            var filter = new BsonDocument();

            Console.WriteLine("count:" + collection.CountDocuments(filter).ToString());


            return(entity);
        }