Rename nested field in BsonDocument with MongoDB.Driver

Question

I have a document, it contains a CustomFields document, in which there are still documents.

How to correctly update the Checkpoint Comment document name to the Checkpoint Comment-test.

I tried as below but it doesn't work.

var filter = Builders<Visit>.Filter;

UpdateDefinition<Visit> update = Builders<Visit>.Update.Rename(x => x.CustomFields.FirstOrDefault(f => f.Name == "Сheckpoint Comment").Name, "Сheckpoint Comment-test");
Collection.UpdateMany(filter.Where(x => true), update);

{
  "_id": ObjectId("61e5707d23516865481ebee7"),
  "CustomFields": {
    "Сheckpoint Comment": {
      "FieldId": ObjectId("6149d5de44175b8324482904"),
      "Type": "Text",
      "ValueBson": "test"
    },
    "Time of arrival at the checkpoint": {
      "FieldId": ObjectId("6149d5de44175b8324482905"),
      "Type": "DateTime",
      "ValueBson": null
    }
  }
}

Answer 1

Solutions

Solution 1

If you apply [BsonElement] attribute to the class' property as below:

public class Visit
{
    public ObjectId Id { get; set; }
    public CustomField CustomFields { get; set; }
}

public class CustomField
{
    [BsonElement("Сheckpoint Comment")]
    public BsonProp Checkpoint { get; set; }
    [BsonElement("Time of arrival at the checkpoint")]
    public BsonProp Time { get; set; }
}

public class BsonProp
{
   public ObjectId FieldId { get; set; }
   public string Type { get; set; }
   public string ValueBson { get; set; }
}

Then specify your field to be renamed as:

UpdateDefinition<Visit> update = Builders<Visit>.Update.Rename(x => x.CustomFields.Checkpoint, "CustomFields.Сheckpoint Comment-test");
Collection.UpdateMany(filter.Empty, update);

---

Solution 2

Without applying [BsonElement] attribute, just specify the field to be renamed in string.

UpdateDefinition<Visit> update = Builders<Visit>.Update.Rename("CustomFields.Сheckpoint Comment", "CustomFields.Сheckpoint Comment-test");
Collection.UpdateMany(filter.Empty, update);

---

Concern & Suggestion

1. The field after rename needs with prefix CustomFields. as "CustomFields.Сheckpoint Comment-test" because you are updating the nested field in an object. Without the prefix CustomFields., Сheckpoint Comment-test will be at the same level as CustomFields, but not inside the CustomFields object.

2. The filter with

filter.Where(x => true)

can be replaced with

filter.Empty

as they are equivalent. (As the first one forces the filter condition definitely true, while the second one applies no filter condition).