In few applications, we have migrations to remove index where we don’t want to raise an error if an index was already removed.
Rails 6.1
adds
a feature, where we can now pass if_exists option to remove_index operation.
This is similar to
if_not_exists
option when we are adding an index on table.
Before
Let’s say we have a comments table with description, post_id and user_id as columns.
We add a data migration to remove the index on the description column.
If this index was already removed the data migration will throw an error as below.
class RemoveDescriptionIndexOnComments < ActiveRecord::Migration[6.0]
def change
remove_index :comments, :description
end
end
rails db:migrate
== 20210320151534 RemoveDescriptionIndexOnComments: migrating ===========================
-- remove_index(:comments, :description)
rails aborted!
StandardError: An error has occurred, this and all later migrations canceled:
No indexes found on comments with the options provided.After
After the changes in Rails 6.1, the above migration will not raise any error
if we pass if_exists as true.
class RemoveDescriptionIndexOnComments < ActiveRecord::Migration[6.1]
def change
remove_index :comments, :description, if_exists: true
end
end
rails db:migrate
== 20210320151534 RemoveDescriptionIndexOnComments: migrating ===========================
-- remove_index(:comments, :description, {:if_exists=>true})
-> 0.0033s
== 20210320151534 RemoveDescriptionIndexOnComments: migrated (0.0034s) ==================Rails does not execute any SQL query for DROP INDEX in the above case.
