diff options
Diffstat (limited to 'doc/development/database/strings_and_the_text_data_type.md')
| -rw-r--r-- | doc/development/database/strings_and_the_text_data_type.md | 35 |
1 files changed, 13 insertions, 22 deletions
diff --git a/doc/development/database/strings_and_the_text_data_type.md b/doc/development/database/strings_and_the_text_data_type.md index 8b839e929c7..33a0fd2ebb7 100644 --- a/doc/development/database/strings_and_the_text_data_type.md +++ b/doc/development/database/strings_and_the_text_data_type.md @@ -11,11 +11,11 @@ info: To determine the technical writer assigned to the Stage/Group associated w When adding new columns that will be used to store strings or other textual information: 1. We always use the `text` data type instead of the `string` data type. -1. `text` columns should always have a limit set by using the `add_text_limit` migration helper. +1. `text` columns should always have a limit set, either by using the `create_table_with_constraints` helper +when creating a table, or by using the `add_text_limit` when altering an existing table. -The `text` data type can not be defined with a limit, so `add_text_limit` is enforcing that by -adding a [check constraint](https://www.postgresql.org/docs/11/ddl-constraints.html) on the -column and then validating it at a followup step. +The `text` data type can not be defined with a limit, so `create_table_with_constraints` and `add_text_limit` enforce +that by adding a [check constraint](https://www.postgresql.org/docs/11/ddl-constraints.html) on the column. ## Background information @@ -48,20 +48,15 @@ class CreateDbGuides < ActiveRecord::Migration[6.0] DOWNTIME = false - disable_ddl_transaction! - def up - unless table_exists?(:db_guides) - create_table :db_guides do |t| - t.bigint :stars, default: 0, null: false - t.text :title - t.text :notes - end - end + create_table_with_constraints :db_guides do |t| + t.bigint :stars, default: 0, null: false + t.text :title + t.text :notes - # The following add the constraints and validate them immediately (no data in the table) - add_text_limit :db_guides, :title, 128 - add_text_limit :db_guides, :notes, 1024 + t.text_limit :title, 128 + t.text_limit :notes, 1024 + end end def down @@ -71,12 +66,8 @@ class CreateDbGuides < ActiveRecord::Migration[6.0] end ``` -Adding a check constraint requires an exclusive lock while the `ALTER TABLE` that adds is running. -As we don't want the exclusive lock to be held for the duration of a transaction, `add_text_limit` -must always run in a migration with `disable_ddl_transaction!`. - -Also, note that we have to add a check that the table exists so that the migration can be repeated -in case of a failure. +Note that the `create_table_with_constraints` helper uses the `with_lock_retries` helper +internally, so we don't need to manually wrap the method call in the migration. ## Add a text column to an existing table |