The prisma documentation gives a quite good hint, when/why it is necessary to specify a name:

When you define two relations between two the same models, you need to add the name argument in the @relation attribute to disambiguate them.

https://www.prisma.io/docs/concepts/components/prisma-schema/relations#disambiguating-relations

How to name the relation is a quite opinionated. Not the right kind of question for Stack Overflow.

Hey @lumenwrites 👋!

We don't have any hard rules about naming but my colleague offered a few guidelines:

1. I would choose a name that semantically describes the relation
2. I also think it’s helpful to include both model names
3. The underscore is used by Prisma to name the relation table in implicit many-to-many relations but it’s not required for relation names

At the end of the day, it's up to personal preference and established team norms.

Let me know if you have any more questions!

General Advice on naming in prisma

Naming is a bit subjective. Normally, I think you should do what makes the most sense for you and your use-case. There are some conventions and rules that Prisma recommends, that you should follow as well:

• Convention for model names
• Convention for field names

However, there aren't any guidelines on naming relations.

Naming for the specific usecases mentioned

In general, go with whatever you think concisely describes the relationship itself. I can give you my personal opinion about the specific naming questions you brought up:

How should relation that describes the User being an author of several Comments be named:

I think UserComments make sense.

I've read somewhere that many-to-many relation names are supposed to start with an underscore.

This is something that Prisma does internally when automatically generating the underlying SQL. You don't have to worry about this at all, nor should you explicitly add a _ at the beginning of a name.

How should the relation that describes the multiples Users being upvoters of multiple Comments be named:

I would go with Upvoters.

Finally, I have a Comment relating to itself for the nested comments. Should this relation be named:

I would probably go with something like CommentResponses or CommentReplies.

You can fix this error by providing two relation fields on PlayerInGame. You have two relation fields on Game. Hence you also need two opposite relation fields on PlayerInGame. In your application logic you have to ensure that only one of those two relation fields is set. So only PlayerInGame.gameAsPlayer1 or PlayerInGame.gameAsPlayer2 should be set according to your business domain.

model User {
  id      Int @id 
  name    String 
}

model Game { 
  id        Int @id 
  player1   PlayerInGame @relation("GamePlayer1")
  player2   PlayerInGame @relation("GamePlayer2")
}

model PlayerInGame {
  id            Int   @id
  player        User
  gameAsPlayer1 Game? @relation("GamePlayer1")
  gameAsPlayer2 Game? @relation("GamePlayer2")
}