Compound unique with a nullable field should allow null

Bug description

Consider the following schema:

model TelemetryMetric {
  action   String
  category String
  id       Int              @id @default(autoincrement())
  label    String?

  @@unique([category, action, label])
}

It would be expected to be able to pass null as a label when using the index. But the definition of the index is:

export type CategoryActionLabelUserIdCompoundUniqueInput = {
  category: string
  action: string
  label: string
}

Casting a null results in a runtime error.

Environment & setup

• OS: All
• Database: PostgreSQL
• Node.js version: 12.X
• Prisma version: 2.3.0

[dpetrick]

NULL != NULL in SQL. We can’t reliably query records that have nulls. Example:

2 rows: ID, category, action, label

1. 1, 1, 2, null
2. 1, 1, 2, null <- this works because SQL null != null, so no unique is violated.

SELECT * FROM TelemetryMetric WHERE category = "1" AND action = "2" AND label = NULL;
SELECT * FROM TelemetryMetric WHERE category = "1" AND action = "2" AND label IS NULL;

The first one doesn’t return anything, which isn’t a surprise if null != null. The practice for nulls is the second one, but that one returns 2 records. Since a unique cursor / where must pin a single record, we can’t allow nulls in the API.

[lstwn]

Having stumbled upon the very same issue, I wanted to ask what the recommended workaround is in this case.

Is it what @Akxe mentioned? I.e. a dummy value instead of null?

I have solved this very same problem using a generated column that is part of the key (either unique or primary (our case))

CREATE TABLE `fotodoc` (
  `orderID` smallint(5) unsigned NOT NULL,
  `itemID` int(11) NOT NULL,
  `groupID` smallint(5) unsigned DEFAULT NULL,
  `groupIDNotNull` smallint(5) GENERATED ALWAYS AS (coalesce(`groupID`,0)) STORED NOT NULL,
  `name` varchar(200) NOT NULL,
  PRIMARY KEY (`orderID`,`itemID`,`groupIDNotNull`)
);

or rather an unique index (e. g. https://stackoverflow.com/questions/8289100/create-unique-constraint-with-null-columns/8289253#8289253)?

Also, do you guys plan to handle this natively with Prisma in the future or do we have to stick to these sql workarounds?

Thanks!