changingColumnType¶

Group destructive · Migrations only · Since 0.15.0
Diagnostic lint/changingColumnType

Sources: inspired by squawk/changing-column-type

Description¶

Changing a column type may require a table rewrite and break existing clients.

Most column type changes require an exclusive lock on the table while the entire table is rewritten. This can take a long time for large tables and will block reads and writes.

Some type changes are safe and don't require a table rewrite:

• Changing to text (binary compatible with varchar/char types)
• Changing to varchar without a length limit
• Dropping a numeric precision constraint (e.g., numeric(10,2) to numeric)

For unsafe type changes, consider creating a new column with the desired type, migrating the data, and then dropping the old column.

Examples¶

Invalid¶

ALTER TABLE "core_recipe" ALTER COLUMN "count" TYPE bigint;

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

  ! Changing a column type requires a table rewrite and blocks reads and writes.

  > 1 │ ALTER TABLE "core_recipe" ALTER COLUMN "count" TYPE bigint;
      │ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    2 │ 

  i Consider creating a new column with the desired type, migrating data, and then dropping the old column.

Valid¶

ALTER TABLE "core_recipe" ALTER COLUMN "edits" TYPE text;

How to configure¶

{
  "linter": {
    "rules": {
      "changingColumnType": "error"
    }
  }
}

How to suppress¶

Suppress this diagnostic with a comment:

-- pgls-ignore changingColumnType