pgroll/examples/23_drop_check_constraint.json

{
  "name": "23_drop_check_constraint",
  "operations": [
    {
      "drop_constraint": {
        "table": "posts",
        "column": "title",
        "name": "title_length",
        "up": "title",
        "down": "(SELECT CASE WHEN length(title) <= 3 THEN LPAD(title, 4, '-') ELSE title END)"
      }
    }
  ]
}
Implement the `drop_constraint` operation (#103) Implement the `drop_constraint` operation for dropping constraints defined on single columns. An example of the operation looks like: ```json { "name": "23_drop_check_constraint", "operations": [ { "drop_constraint": { "table": "posts", "column": "title", "name": "title_length", "up": "title", "down": "(SELECT CASE WHEN length(title) <= 3 THEN LPAD(title, 4, '-') ELSE title END)" } } ] } ``` for dropping a `CHECK` constraint. And like this for dropping a `FOREIGN KEY` constraint: ```json { "name": "24_drop_foreign_key_constraint", "operations": [ { "drop_constraint": { "table": "posts", "column": "user_id", "name": "fk_users_id", "up": "user_id", "down": "(SELECT CASE WHEN EXISTS (SELECT 1 FROM users WHERE users.id = user_id) THEN user_id ELSE NULL END)" } } ] } ``` The operation works very similarly to the inverse operation of adding `CHECK` and `FOREIGN KEY` constraints to a single column. * On `Start`: * a new column without the constraint is added to the underlying table. * triggers are created using the `up` and `down` SQL. The `down` SQL needs to ensure that rows inserted into the new view that don't meet the constraint are converted into rows that do meet the constraint. * On `Complete` * Triggers are removed, the old column is deleted and the new column is renamed. * On `Rollback` * The new column and the triggers are removed. ## Improvements * The `drop_constraint` operation requires that the column on which the constraint is defined is named in the migration `json` file. If `pg-roll`'s internal schema representation knew about the constraints defined on a table it would be possible to delete constraints by constraint name only; the schema representation would know on which column the constraint was defined. * `pg-roll` currently only allows for creating `CHECK` and `FOREIGN KEY` constraints on single columns; this limitation also applies to the `drop_constraint` operation. 2023-09-19 07:32:53 +03:00			`{`
			`"name": "23_drop_check_constraint",`
			`"operations": [`
			`{`
			`"drop_constraint": {`
			`"table": "posts",`
			`"column": "title",`
			`"name": "title_length",`
			`"up": "title",`
			`"down": "(SELECT CASE WHEN length(title) <= 3 THEN LPAD(title, 4, '-') ELSE title END)"`
			`}`
			`}`
			`]`
			`}`