Last week I wrote Using Active Support Concerns to Encapsulate Data Access and Validation, where I explained how to use Active Support concerns to define data access and validation rules for an Active Record enum attribute. The attribute mapped values to integers in the database, similar to this example:
class Project < ActiveRecord::Base
enum status: [ :active, :archived ]
validates :status, inclusion: { in: statuses.keys }
end
Depending on the problem that you are trying to solve, this approach could potentially lead to several drawbacks including:
- Meaningless integer values stored in the database.
- Unless the integer value is "limited" in a migration, Active Model validations can be by-passed through plain SQL, effectively allowing the attribute to be set to any integer.
- Plain SQL queries need to use the integer value, not the Active Record enum.
In this blog post, I'll show how to use the Postgres enum type with Rails to avoid the aforementioned pit falls.
Postgres Enumerated Types
Postgres supports enumerated types, which are data types that comprise a static, ordered set of values. To create an enum type, use the Postgres CREATE TYPE
command. In a Rails project, generate a migration as follows rails g migration AddStatusToProjects
:
class AddStatusToProjects < ActiveRecord::Migration[5.2]
def up
execute <<-SQL
CREATE TYPE project_status AS ENUM ('active', 'archived');
SQL
add_column :projects, :status, :project_status
end
def down
remove_column :projects, :status
execute <<-SQL
DROP TYPE project_status;
SQL
end
end
The migration creates a project_status
enumerated type. Next, it adds a status
column to the projects
table of type project_status
. By using the Postgres enumerated type, the status
attribute is constrain at the database level to be one of active
|archived
. Lastly, set config.active_record.schema_format = :sql
in the environment configuration files, so that the database schema includes the project_status
enumerated type definition.
Active Record Enum
The initial definition of the status
Active Record enum needs to be slightly modified. Simply use a hash to explicitly map the relation between the attribute and database value as follows:
class Project < ActiveRecord::Base
enum status: { active: 'active', archived: 'archived' }
validates :status, inclusion: { in: statuses.keys }
end
Unit Tests
Unit tests can be tremendously simplified by using the shoulda-matchers
gem:
RSpec.describe Project, type: :model do
it { should define_enum_for(:status).
with_values(
active: 'active',
archived: 'archived'
).backed_by_column_of_type(:enum) }
it { should allow_values(:active, :archived).for(:status) }
end
The first unit test verifies the status
column is defined in the Project
model and its column type is enum
. Also, it makes sure the status
enum values are correctly defined as specified in the status
hash. Finally, the last test confirms the Project
model allows the status
attribute to be set using the :active
and :archived
symbols.
Conclusion
And that was it! The Project
model defines and validates an enum for the status
attribute which is mapped to meaningful string values in the database. Additionally, the status
column is constrain at the database level to be one of the specified values in the Postgres enumerated type.
If you are interested in learning more about enum in Rails, I highly recommend reading Ruby on Rails - how to create perfect enum in 5 steps. This blog post, written by Błażej Pichur, has been a fantastic guide during the past few weeks to improve my understanding and usage of enum in Rails.
Top comments (5)
Unfortunately, this approach has the downside of breaking the db/schema.rb file.
I can reproduce the behavior on Rails 5.17, 5.2.2.4, and 6.0.3
if I do...
then my schema file is messed up, specifically, the schema users table doesn't get output whatseover, and instead in its place is this message
Could not dump table "users" because of following StandardError
Unknown type 'xyz_setting' for column 'xyz'
I think maybe there's a gem I found that fixes this.
Did you try setting
config.active_record.schema_format = :sql
in the environment configuration files?Ah yes, this works as expected and leaves you with no more
db/schema.rb
file and instead adb/structure.sql
file written in the native SQL Postgres commands instead of the Rails schema syntax.github.com/jasonfb/R5244EnumIssueTest
stackoverflow.com/questions/646689...