banDropGeneratedExpression¶

Group destructive · Migrations only · Since Unreleased
Diagnostic lint/banDropGeneratedExpression

Sources: inspired by squawk/ban-drop-generated-expression

Description¶

Dropping the expression of a generated column may break existing clients.

DROP EXPRESSION turns a stored generated column into an ordinary column. Existing values remain, but Postgres no longer computes the value for new or updated rows, so clients that omit the column write NULL instead of the computed value.

Examples¶

Invalid¶

alter table line_items alter column total drop expression;

code-block.sql:1:1 lint/banDropGeneratedExpression ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ! Dropping the expression of generated column total may break existing clients.

  > 1 │ alter table line_items alter column total drop expression;
      │ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    2 │ 

  i Postgres no longer computes the column, so inserts and updates that omit it write NULL.

  i Update clients to write the column themselves before dropping the expression.

How to configure¶

{
  "linter": {
    "rules": {
      "banDropGeneratedExpression": "error"
    }
  }
}

How to suppress¶

Suppress this diagnostic with a comment:

-- pgls-ignore banDropGeneratedExpression