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Improves Active Record Migrations guide on add_foreign_key

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Lists additional options and adds a link to the API of the `add_foreign_key`
method. The `name` option is removed because it is not essential and its
extensive description can remain in the API.
This commit is contained in:
Eike Send 2021-12-08 22:40:24 +01:00
parent c76588b58e
commit f9d28f39f8
1 changed files with 17 additions and 11 deletions
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guides/source/active_record_migrations.md
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@ -548,15 +548,22 @@ While it's not required you might want to add foreign key constraints to
add_foreign_key :articles, :authors
```
This adds a new foreign key to the `author_id` column of the `articles`
table. The key references the `id` column of the `authors` table. If the
column names cannot be derived from the table names, you can use the
`:column` and `:primary_key` options.
This `add_foreign_key` call adds a new constraint to the `articles` table.
The constraint guarantees that a row in the `authors` table exists where
the `id` column matches the `articles.author_id`.
Rails will generate a name for every foreign key starting with
`fk_rails_` followed by 10 characters which are deterministically
generated from the `from_table` and `column`.
There is a `:name` option to specify a different name if needed.
If the `from_table` column name cannot be derived from the `to_table` name,
you can use the `:column` option. Use the `:primary_key` option if the
referenced primary key is not `:id`.
For example add a foreign key on `articles.reviewer` referencing `authors.email`:
```ruby
add_foreign_key :articles, :authors, column: :reviewer, primary_key: :email
```
Options such as `name`, `on_delete`, `if_not_exists`, `validate` and `deferrable`
are described in the [`add_foreign_key`][] API.
NOTE: Active Record only supports single column foreign keys. `execute` and
`structure.sql` are required to use composite foreign keys. See
@ -570,11 +577,10 @@ remove_foreign_key :accounts, :branches
# remove foreign key for a specific column
remove_foreign_key :accounts, column: :owner_id
# remove foreign key by name
remove_foreign_key :accounts, name: :special_fk_name
```
[`add_foreign_key`]: https://api.rubyonrails.org/classes/ActiveRecord/ConnectionAdapters/SchemaStatements.html#method-i-add_foreign_key
### When Helpers aren't Enough
If the helpers provided by Active Record aren't enough you can use the [`execute`][]