Why "null" can't be the default value of a nullable column?

Question

Consider this schema:

model Comment {
  id        Int        @id @default(autoincrement())
  reply     Comment?   @relation(fields: [replyId], references: [id], onDelete: SetNull)
  replyId   Int?       @default(null)
  comment   String
}

Here both reply and replyId are nullable. When I migrate I get this error:

error: Error parsing attribute "@default": Expected a numeric value, but received literal value "Null".
  -->  schema.prisma:70
   |
69 |   reply     Comment? @relation(fields: [replyId], references: [id], onDelete: SetNull)
70 |   replyId   Int?     @default(null)
   |

Why?

score 25 · Accepted Answer · answered Aug 09 '21 at 03:25

25

You don't really need to specify a null default value for an optional field. If you don't specify Comment relation or explicitly provide the replyId value for a record, then the value of replyId is automatically null. This is true for optional fields that are not acting as foreign keys as well.

So, the behavior you want would be there automatically, there's no need to define @default(null).

answered Aug 09 '21 at 03:25

Tasin Ishmam

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Thank you. you are the only person that answers my Prisma questions:). I thought that because replyId is an integer, its default value is 0. – Arman Aug 09 '21 at 03:49
Optional fields, regardless of the type are nullable and defaults to null. And happy to help :D – Tasin Ishmam Aug 09 '21 at 04:04
yep the "Int?" actually means, set to null if nothing is provided. – kiwicomb123 Feb 17 '22 at 05:59
There is however a use case where someone would want to have NULL as default rather than undefine. For instance, PostgreSQL guarantees 'uniqueness' for NULL fields but not for undefined. – Nditah Jun 19 '22 at 15:06
I have same problem. I follow this answer to used `DateTime?` optional type data and work to create default `NULL` :D – Rahmat Oktrifianto Oct 25 '22 at 01:47
this is not true for mongodb – James Tan Nov 20 '22 at 15:52

Why "null" can't be the default value of a nullable column?

1 Answers1