MongoDB C# Bulk Update of nested array elements

I was hoping that someone could point me in the right direction here

I'm trying to leverage MongoDB’s C# driver (ver2.19.1) bulk update functionality. I wanted to update all matches of old value (URL in my example) with a new one in all documents within my collection.
It tried to follow directions provided by MongoDBs example provided here, “Update Many Documents”.

The C# filter and update statement as shown below but it produces an error --- I've been struggling to work out why but I believe its associated with finding and updating elements of an embedded array within my saved documents.

Here’s the code that produces the error:

public void UpdateUrlsMany(string originalUrl, string newUrl, string collectionName)
    {
        var articlesCol = _database.GetCollection<Document>(collectionName);

        var filter = Builders<Document>.Filter.Eq("Paragraphs.Images.Url", originalUrl);
        var update = Builders<Document>.Update.Set("Paragraphs.Images.Url", newUrl);
     
        articlesCol.UpdateMany(filter, update); //<- error occurs here
    }

Error produced when update is executed.
“MongoDB.Driver.MongoBulkWriteException`1[…Document] : A bulk write operation resulted in one or more errors. WriteErrors: [ { Category : "Uncategorized", Code : 28, Message : "Cannot create field 'Images' in element … “

An example of the JSON housed with MongoDB collection looks like this for reference.

[
  {
    "_id": "527c61082241f813c09c711c",
    "Paragraphs": [
      {
        "Data": "some info",
        "Images": [
          {
            "Title": "",
            "Url": "i/folder1/path0_1.jpg"
          }
        ]
      },
      {
        "Data": "some info",
        "Images": [
          {
            "Title": "some title…",
            "Url": "i/folder1/path0_2.jpg"
          }
        ]
      }
    ]
  },
  {
    "_id": "527c61092241f813c09c7012",
    "Paragraphs": [
      {
        "Data": "some info",
        "Images": [
          {
            "Title": "title text",
            "Url": "i/folder2/path1_1.jpg"
          },
          {
            "Title": " title text ",
            "Url": "i/folder2/path1_2.jpg"
          }

        ]
      },
      {
        "Data": "some info",
        "Images": [
          {
            "Title": "title text ….",
            "Url": "i/folder2/path2_0.jpg"
          }
        ]
      }
  }
]

Thanks for any assistance

The error is because the wrapper creates a query providing a path as "Paragraphs.Images.Url". Exactly it creates:

    db.collection.updateMany(
      {
        "Paragraphs.Images.Url": "existingurl"
},
{
  $set: {
    "Paragraphs.Images.Url": "newurl"
  }
})

Thus the error "Cannot create field 'Images' in element … “ since that path does not exist and it is also a nested collection. In order to make it work you need to create nested elements as:

db.collection.updateMany(
  {
    "Paragraphs.Images.Url":
      "existingurl",
  },
  {
    $set: {
      Paragraphs: {
        Images: {
          Url: "newurl",
        },
      },
    },
  }
);

Update

A potential asynchronous solution given that it can perform a mass update is as follows:

  private static async Task<UpdateResult> UpdateManyUrlAsync(string originalUrl, string newUrl, string collectionName)
        {
            var articlesCol = _database.GetCollection<Document>(collectionName);         

            var filter = Builders<Document>.Filter.Eq("Paragraphs.Images.Url", originalUrl);
            var update = Builders<Document>.Update.Set("Paragraphs.$.Images.$[].Url", newUrl);

            return await collection.UpdateManyAsync(filter, update);
            
        }

The problem is that you can't directly set the field value when the field is in the array.

You need to work with $[<identifier>] filtered positional operator.

Either:

db.collection.update({
  "Paragraphs.Images.Url": /* originalUrl */
},
{
  $set: {
    "Paragraphs.$.Images.$[].Url": /* newUrl */
  }
})

var filter = Builders<Document>.Filter.Eq("Paragraphs.Images.Url", originalUrl);
var update = Builders<Document>.Update.Set("Paragraphs.$.Images.$[].Url", newUrl);
     
articlesCol.UpdateMany(filter, update);

Or:

db.collection.update({
  "Paragraphs.Images.Url": /* originalUrl */
},
{
  $set: {
    "Paragraphs.$.Images.$[image].Url": /* newUrl */
  }
},
{
  arrayFilters: [
    {
      "image.Url": /* originalUrl */
    }
  ]
})

var filter = Builders<Document>.Filter.Eq("Paragraphs.Images.Url", originalUrl);
var update = Builders<Document>.Update.Set("Paragraphs.$.Images.$[image].Url", newUrl);

var arrayFilters = new[]
{
    new BsonDocumentArrayFilterDefinition<Document>(
        new BsonDocument("image.Url", originalUrl)
    )
};

articlesCol.UpdateMany(filter, update, 
    options: new UpdateOptions { ArrayFilters = arrayFilters });