Why it is not possible to ReplaceOne document with different _id than the existing one?

Working with Data Drivers
,
1

Hi, I’ve just found out that it is not possible to replace document using ReplaceOne (or FindOneAndReplace) while existing document and the new document have different _id, BUT while also filtering by other properties than _id. I would like to know why?

Here is an example:

await collection.ReplaceOneAsync(
doc => doc.Property1 == entity.Property1 && doc.Property2 == entity.Property2,
entity,
new ReplaceOptions() { IsUpsert = true },
ct);

‘entity’ object has the Id field set (GUID) and different than doc _id that is found by filter conditions (Property1 and Property2).

The error I am getting:
‘A bulk write operation resulted in one or more errors. WriteErrors: [ { Category : “Uncategorized”, Code : 66, Message : “After applying the update, the (immutable) field ‘_id’ was found to have been altered to _id: UUID(”{guid-id}“)” } ].’

Thanks to anybody who knows why there is this constrain (or feature). :slight_smile:

2

Hi @Ondrej_Svacina ,

Welcome to the MongoDB Community Forums! Are you specifying the _id field of the new entity or is it auto generated? You can find more details about replacing a document using the .NET/C# driver here. Please note that the _id field itself is immutable for a document once inserted. On the other hand, IsUpsert is used when you want to insert the document if no documents match the query filter specified. Hope that helps.

Thanks,

Rishit.

3

Hi @Rishit_Bhatia ,

thanks for the response.

Yes, I’m specifying _id field as GUID in my application, so both existing document in DB and new replacing entity have GUID _id.

I understand that I cannot update _id field when UPDATING document, but I am trying to REPLACE whole document, moreover in ReplaceOne function I am filtering by other fields, not by _id. So I am curious why this is not possible.

4

Hi @Ondrej_Svacina ,

What you’re mentioning is possible. Looking at the error while trying to replicate this, this is happening because the default value of the _id is being serialized. There are two ways of doing this type of upsert:

  1. Configure the POCO to NOT serialize the default _id value
[BsonIgnoreIfDefault]
[BsonGuidRepresentation(GuidRepresentation.Standard)]
public Guid Id { get; set; }
  1. Assign the _id value for the new entity to be same as the one you are trying to replace.

As you can see in the replacement parameter here, The <replacement> document cannot specify an _id value that differs from the replaced document.

We’ll update our documentation to clarify this further. Let me know if that works for you.

Thanks,

Rishit.