MongoDB - How to update a single object in the array of objects inside a document

Question

I have the following document structure:

{
  "Agencies": [
    {
      "name": "tcs",
      "id": "1",
      "AgencyUser": [
        {
          "UserName": "ABC",
          "Code": "ABC40",
          "Link": "http.ios.com",
          "TotalDownloads": 0
        },
        {
          "UserName": "xyz",
          "Code": "xyz20",
          "Link": "http.ios.com",
          "TotalDownloads": 0
        }
      ]
    }
  ]
}

Like I have multiple agencies and each agency contains a list of agents.

What I am trying is to pass the Code and update the TotalDownloads field of the agent that matches the code.

For example, if someone uses the code ABC40 so I need to update the field TotalDownloads of the agent called "ABC".

What I have tried is as below:

public virtual async Task UpdateAgentUsersDownloadByCode(string Code)
{
    var col = _db.GetCollection<Agencies>(Agencies.DocumentName);
    FilterDefinition<Agencies> filter = Builders<Agencies>.Filter.Eq("AgencyUsers.Code", Code);
    UpdateDefinition<Agencies> update = Builders<Agencies>.Update.Inc(x => x.AgencyUsers.FirstOrDefault().TotalDownloads, 1);
    await col.UpdateOneAsync(filter, update);
}

It is giving me the following error:

Unable to determine the serialization information for x => x.AgencyUsers.FirstOrDefault().TotalDownloads.

Where I'm wrong?

Answer 1

Note: From the attached sample document, the array property name: AgencyUser is not matched with the property name that you specified in the update operation, AgencyUsers.

---

Use arrayFilters with $[<identifier>] positional filtered operator to update the element(s) in the array.

MongoDB syntax

db.Agencies.update({
  "AgencyUsers.Code": "ABC40"
},
{
  $inc: {
    "AgencyUsers.$[agencyUser].TotalDownloads": 1
  }
},
{
  arrayFilters: [
    {
      "agencyUser.Code": "ABC40"
    }
  ]
})

Demo @ Mongo Playground

MongoDB .NET Driver syntax

UpdateDefinition<Agencies> update = Builders<Agencies>.Update
    .Inc("AgencyUsers.$[agencyUser].TotalDownloads", 1);

UpdateOptions updateOptions = new UpdateOptions
{
    ArrayFilters = new[]
    {
        new BsonDocumentArrayFilterDefinition<Agencies>(
            new BsonDocument("agencyUser.Code", Code)
            )
    }
};
UpdateResult result = await col.UpdateOneAsync(filter, update, updateOptions);

Demo