MongoDB C# .NET – Update Nested array examples

Today in this article will see MongoDB C# .NET – Update Nested array examples in .NET or .NET Core application.

We already looked at a simple way of adding or updating a nested array field to the document in general. We shall use positional operator $[ ] for updating the array field .

Today in this article, we will cover below aspects,

Please visit the below article to understand other basic simple scenarios on adding or updating mongo documents,

• Add/Update New field to all document using UpdateMany in a MongoDB Collection Part-I

We shall use the below sample JSON document and will try to update the below-highlighted value for the given filter criteria.

Sample Schema example

{
  "UserId": 999999,
  "DateAdded": "TEST2",
  "Books": [
    {
      "book_name": "book_name1",
      "price": 88,
      "config": [
        {
          "key": "Test1",
          "value": "60"
        }
      ]
    },
    {
      "book_name": "book_name2",
      "price": 50,
      "config": [
        {
          "key": "test2",
          "value": "60"
        },
        {
          "key": "test4",
          "value": "100"
        }
      ]
    }
  ]
}

Getting started

Please create any .NET/.NET Core application.

Please add the MongoDB driver NuGet package using the Nuget Package manager.

PM> Install-Package MongoDB.Driver -Version 2.9.3

I shall keep the MongoDB driver interface used here simple enough to concentrate on how to update deeply nested array documents.

Step I – Establish the connection to the Database using MongoDB driver,

var _mongoClient = new MongoClient("mongodb://your connection string");
var db = _mongoClient.GetDatabase("Book");

Please visit for better approaches like using DI or IOC here,

• Getting Started MongoDB in .NET Core with Examples

• MongoDB Repository implementation in .NET Core with example

Step II – MongoDB Update nested array

 await collection.UpdateOneAsync(x => x.userid == inputUserId,
                Builders<Library>.Update.Set("books.$[g].config.$[c].value", inputValue),
                new UpdateOptions
                {
                    ArrayFilters = new List<ArrayFilterDefinition>
                    {
                        new BsonDocumentArrayFilterDefinition<BsonDocument>(new BsonDocument("g.book_name", inputBookName)),
                        new BsonDocumentArrayFilterDefinition<BsonDocument>(new BsonDocument("c.key", key))
                    }
                });

In the above code, the positional operator $[] identifies the array elements that match the arrayFilters conditions for an update operation.

After the successful execution of the query, we shall see the value gets updated correctly.

• MongoDB – Implement Batch for CRUD operations

Do you have any comments or ideas or any better suggestions to share?

Please sound off your comments below.

Happy Coding !!

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