MongoDb C# Updating elements at array element

Question

i have the following document structure:

{
   "name":"Test Online",
   "strategies":[
      {
         "strategyType":"Online",
         "strategyBudget":0,
         "extraElements":{
            "URL":"http:\\www.google.com"
         }
      },
      {
         "strategyType":"TV",
         "strategyBudget":0,
         "extraElements":{
            "ChannelSlots":[
               {
                  "channelName":"SIC",
                  "fromHour":"13:30:00",
                  "toHour":"13:30:00"
               },
               {
                  "channelName":"TVI",
                  "fromHour":"15:30:00",
                  "toHour":"16:30:00"
               }
            ]
         }
      },
      {
        "strategyType":"Outdoor",
        "strategyBudget":2000,
        "extraElements":{
            "Latitude": 8.123456,
            "Longitude": -16.123456

        }
      }

   ],
   "campaignBudget":3000
}

I want to create a function that gather the campaign Budget, divide it equally by all defined strategies (in this case 3) and then updates for each strategy the strategyBudget Field.

I have created all necessary objects so that i can do this in a typesafe way. For example i have for the strategy:

    [BsonDiscriminator("StrategyType", RootClass = true, Required = true)]
    [BsonKnownTypes(
        typeof(OnlineStrategy), 
        typeof(TvStrategy), 
        typeof(OutdoorStrategy))]
    public class Strategy
    {

        [JsonConverter(typeof(StringEnumConverter))]  // JSON.Net
        [BsonRepresentation(BsonType.String)]  // Mongo
        public  StrategyType StrategyType { get; set; }

        [JsonProperty("strategyBudget")]
        public  int StrategyBudget { get; set; }

        [JsonProperty("extraElements")]
        public ExtraElements ExtraElements { get; set; }
    }
}

so i can call Strategy.StrategyBudget and i get or set the budget.

My function so far is:

/**
         * Divide the budget of a campaign equally between all defined strategies for that campaign
         * so if a campaign has 3000 of budget and 3 strategies, 
         * each strategy would get 1000, and the campaign budget is set to 0
         */
        private void DivideBudgetEqually(string campaignID)
        {
            Campaign campaignRecord = _campaigns.Find(cpg => cpg.Id == campaignID).FirstOrDefault();
            int campaignBudget = campaignRecord.CampaignBudget;
            int numStrategies = campaignRecord.Strategies.Count;

            int equalBudget = campaignBudget / numStrategies;

            var campaignFilter = Builders<Campaign>.Filter.Eq(cpg => cpg.Id, campaignID);

            var strategyUpdate = Builders<Campaign>.Update.Set(cpg => cpg.Strategies[-1].StrategyBudget, equalBudget);
            var campaignUpdate = Builders<Campaign>.Update.Set(cpg => cpg.CampaignBudget, 0);

            // update the each strategy budget to equal value
            var resultStrategy = _campaigns.UpdateMany(campaignFilter, strategyUpdate);

            // update the campaign budget to 0, since we've distributed all the budget to the strategies
            var resultCampaign = _campaigns.UpdateMany(campaignFilter, campaignUpdate);


        }

But when i call the endpoint to execute this, i get the following:

web_1                  | fail: Microsoft.AspNetCore.Server.Kestrel[13]
web_1                  |       Connection id "0HLVNUBP8QGRB", Request id "0HLVNUBP8QGRB:00000001": An unhandled exception was thrown by the application.
web_1                  | MongoDB.Driver.MongoWriteException: A write operation resulted in an error.
web_1                  |   The positional operator did not find the match needed from the query.
web_1                  |  ---> MongoDB.Driver.MongoBulkWriteException`1[semasio_challenge_2.Models.Campaign]: A bulk write operation resulted in one or more errors.
web_1                  |   The positional operator did not find the match needed from the query.
web_1                  |    at MongoDB.Driver.MongoCollectionImpl`1.BulkWrite(IClientSessionHandle session, IEnumerable`1 requests, BulkWriteOptions options, CancellationToken cancellationToken)
web_1                  |    at MongoDB.Driver.MongoCollectionImpl`1.<>c__DisplayClass23_0.<BulkWrite>b__0(IClientSessionHandle session)
web_1                  |    at MongoDB.Driver.MongoCollectionImpl`1.UsingImplicitSession[TResult](Func`2 func, CancellationToken cancellationToken)
web_1                  |    at MongoDB.Driver.MongoCollectionImpl`1.BulkWrite(IEnumerable`1 requests, BulkWriteOptions options, CancellationToken cancellationToken)
web_1                  |    at MongoDB.Driver.MongoCollectionBase`1.<>c__DisplayClass92_0.<UpdateMany>b__0(IEnumerable`1 requests, BulkWriteOptions bulkWriteOptions)
web_1                  |    at MongoDB.Driver.MongoCollectionBase`1.UpdateMany(FilterDefinition`1 filter, UpdateDefinition`1 update, UpdateOptions options, Func`3 bulkWrite)
web_1                  |    --- End of inner exception stack trace ---
web_1                  |    at MongoDB.Driver.MongoCollectionBase`1.UpdateMany(FilterDefinition`1 filter, UpdateDefinition`1 update, UpdateOptions options, Func`3 bulkWrite)
web_1                  |    at MongoDB.Driver.MongoCollectionBase`1.UpdateMany(FilterDefinition`1 filter, UpdateDefinition`1 update, UpdateOptions options, CancellationToken cancellationToken)
web_1                  |    at semasio_challenge_2.Services.CampaignService.DivideBudgetEqually(String campaignID) in /src/Services/CampaignService.cs:line 109

If i change the update function to any Async version, this error doesn't happen, but startegyBudget is not updated, but campaign one is.

What i'm doing wrong here?

Kevin Smith · Accepted Answer · 2020-05-14 13:40:42Z

1

Your campaignFilter needs to match one of the documents in the array in which you want to update with the positional operator $.

This:

var campaignFilter = Builders<Campaign>.Filter.Eq(cpg => cpg.Id, campaignID);

Needs to change to something like:

var campaignFilter = Builders<Campaign>.Filter.Eq(cpg => cpg.Id, campaignID)
                 & Builders<Campaign>.Filter.ElemMatch(cpg => cpg.Strategies, x => x.FieldToMatch == "test");

answered May 14, 2020 at 13:40

Kevin Smith

14.5k5 gold badges63 silver badges88 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Sorcerer86pt Over a year ago

This worked like a charm:

var campaignFilter = Builders<Campaign>.Filter.Eq(cpg => cpg.Id, campaignID)                  & Builders<Campaign>.Filter.ElemMatch<Strategy>(cpg => cpg.Strategies, x => x.StrategyBudget != equalBudget);

Sorcerer86pt Over a year ago

Well, it's only updating the first strategy. I'm using UpdateManyAsync.

Kevin Smith Over a year ago

The positional operator will only update the first matched element in the array, the UpdateMany is for updating multiple documents, not array items.

Kevin Smith Over a year ago

If you want to do something more complex with updating arrays in documents look at array filters - docs.mongodb.com/manual/reference/operator/update/…

Sorcerer86pt · Accepted Answer · 2020-05-18 11:07:30Z

For reference, and using the Array Filters suggestion from Kevin Smith this is the code that executed that operation (since the usage of Array Filter in C# has few examples):

            var campaignFilter = Builders<Campaign>.Filter.Eq(cpg => cpg.Id, campaignID);
            // mongo c# driver has yet to have a fluent syntax for Array Filters.
            var updateDefinition = Builders<Campaign>.Update.Set("Strategies.$[stra].StrategyBudget", equalBudget);

            var arrayFilterStratergy = new List<ArrayFilterDefinition>();
            arrayFilterStratergy.Add(
                 new BsonDocumentArrayFilterDefinition<BsonDocument>(new BsonDocument("stra.StrategyBudget", new BsonDocument("$gte", 0)))
            );

            // update the each strategy budget to equal value
            var resultStrategy = await _campaigns.UpdateOneAsync(
                campaignFilter,
                updateDefinition,
                new UpdateOptions { ArrayFilters = arrayFilterStratergy });

Collectives™ on Stack Overflow

MongoDb C# Updating elements at array element

2 Answers 2

4 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

4 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related