Generated columns (PostgreSQL)

Problem

Postgres generated columns are currently not supported. That’s not a big deal, since we can always declare them as regular columns in the schema.prisma. The only flaw is we need to declare them as optional, otherwise the client will always complain about them missing in the create input. This means the generated type field will always be “nullable”, when it’s actually not.

Suggested solution

Introduce a custom schema attribute ( ex @generated ) to mark a column as a postgres generated column. This way it will not be included in the create input type but it will also be not null in the model type.

[andyjy]

Update: issue created https://github.com/prisma/prisma/issues/14799

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I’m seeing a related issue which is that prisma inspects the database schema for a generated column I want it to not attempt to manage and writes into any new migrations ALTER TABLE <> ALTER COLUMN <generated_thing> DROP DEFAULT;

@ryanmt I’ve just run into this after upgrading to Prisma 4 - these unwanted (+invalid!) DROP DEFAULT migrations were not being generated previously, so now I’ve hit a blocker preventing me creating new migrations.

Are you using Prisma v4 also? Could you possibly share more about your workaround?

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In my schema.prisma (worked for the past months with Prisma v3):

...
<column> String? @db.VarChar(255) @default(dbgenerated())
...

A previous custom migration in my migrations history results in the following schema in Postgres (which has been working fine):

"<column>" character varying(255) GENERATED ALWAYS AS (
<SQL expression>) STORED

Upgrading to Prisma v4 now generates these new DROP DEFAULT migrations that fail with error:

Database error:
ERROR: column "<column>" of relation "<table>" is a generated column
HINT: Use ALTER TABLE ... ALTER COLUMN ... DROP EXPRESSION instead.

[pantharshit00]

I think you can already use @default(dbgenerated()) here to specify that field is computed. We already support that. https://www.prisma.io/docs/reference/api-reference/prisma-schema-reference#dbgenerated

What we don’t do here is automatically add this for computed fields when we introspect so that is something that we should do. cc @do4gr