SchemaPlus provides ActiveRecord support for foreign keys, database defined validations and associations.
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SchemaPlus is an ActiveRecord extension that provides enhanced capabilities for schema definition and querying, including: enhanced and more DRY index capabilities, support and automation for foreign key constraints, and support for views.

For added rails DRYness see also the gems schema_associations and schema_validations

Dependency Status


SchemaPlus supports all combinations of:

  • rails 3.2

  • PostgreSQL, MySQL (using mysql or mysql2 gem), or SQLite3 (using sqlite3 3.7.7 which has foreign key support)

  • MRI ruby 1.9.2 or 1.9.3

Note: As of version 1.0.0, SchemaPlus no longer supports rails 2.3, 3.0 and 3.1 and ruby 1.8.7. The last version to support them was 0.4.1.


Install from via

$ gem install "schema_plus"

or in a Gemfile

gem "schema_plus"


Here some examples that show off the high points. For full details see the RDoc documentation.


With standard rails migrations, you specify indexes separately from the table definition:

# Standard Rails approach...
create_table :parts do |t|
  t.string :name
  t.string :product_code

add_index :parts, :name     # index repeats table and column names and is defined separately
add_index :parts, :product_code, unique: true

But with SchemaPlus you can specify your indexes when you define each column, with options as desired

# More DRY way...
create_table :parts do |t|
  t.string :name,           index: true
  t.string :product_code,   index: { unique: true }

The options hash can include an index name:

t.string :product_code,     index: { unique: true, name: "my_index_name" }

You can also create multi-column indexes, for example:

t.string :first_name
t.string :last_name,        index: { with: :first_name }

t.string :country_code
t.string :area_code
t.string :local_number      index: { with: [:country_code, :area_code], unique: true }

And you can specify index orders:

t.string :first_name
t.string :last_name,        index: { with: :first_name, order: :first_name: :desc, last_name: :asc}}

As a convenient shorthand, the :unique option can be specified as

t.string :product_code,   index: :unique

which is equivalent to

t.string :product_code,   index: { unique: true }

If you're using Postgresql, SchemaPlus provides support for conditions, expressions, index methods, and case-insensitive indexes:

t.string :last_name,  index: { conditions: 'deleted_at IS NULL' }
t.string :last_name,  index: { expression: 'upper(last_name)' }
t.string :last_name,  index: { kind: 'hash' }
t.string :last_name,  index: { case_sensitive: false }        # shorthand for expression: 'lower(last_name)'

These features are available also in ActiveRecord::Migration.add_index. See doc at SchemaPlus::ActiveRecord::ConnectionAdapters::PostgresqlAdapter and SchemaPlus::ActiveRecord::ConnectionAdapters::IndexDefinition

When you query column information using ActiveRecord::Base#columns, SchemaPlus analogously provides index information relevant to each column: which indexes reference the column, whether the column must be unique, etc. See doc at SchemaPlus::ActiveRecord::ConnectionAdapters::Column

SchemaPlus also tidies some index-related behavior:

  • Rails' various db adapters have inconsistent behavior regarding an attempt to create a duplicate index: some quietly ignore the attempt, some raise an error. SchemaPlus regularizes the behavor to ignore the attempt for all db adapters.

  • If you rename a table, indexes named using rails' automatic naming convention will be renamed correspondingly.

Foreign Key Constraints

SchemaPlus adds support for foreign key constraints. In fact, for the common convention that you name a column with suffix _id to indicate that it's a foreign key, SchemaPlus automatically defines the appropriate constraint.

SchemaPlus also creates foreign key constraints for rails' t.references or t.belongs_to, which take the singular of the referenced table name and implicitly create the column suffixed with _id.

You can explicitly specify whether or not to generate a foreign key constraint, and specify or override automatic options, using the :foreign_key keyword

Here are some examples:

t.integer :author_id                                 # automatically references table 'authors', key id
t.integer :parent_id                                 # special name parent_id automatically references its own table (for tree nodes)
t.integer :author_id, foreign_key: true           # same as default automatic behavior
t.integer :author,    foreign_key: true           # non-conventional column name needs to force creation, table name is assumed to be 'authors'
t.integer :author_id, foreign_key: false          # don't create a constraint

t.integer :author_id, foreign_key: { references: :authors }        # same as automatic behavior
t.integer :author,    foreign_key: { reference: :authors}          # same default name
t.integer :author_id, foreign_key: { references: [:authors, :id] } # same as automatic behavior
t.integer :author_id, foreign_key: { references: :people }         # override table name
t.integer :author_id, foreign_key: { references: [:people, :ssn] } # override table name and key
t.integer :author_id, foreign_key: { references: nil }             # don't create a constraint
t.integer :author_id, foreign_key: { name: "my_fk" }               # override default generated constraint name
t.integer :author_id, foreign_key: { on_delete: :cascade }
t.integer :author_id, foreign_key: { on_update: :set_null }
t.integer :author_id, foreign_key: { deferrable: true }

Of course the options can be combined, e.g.

t.integer :author_id, foreign_key: { name: "my_fk", on_delete: :no_action }

As a shorthand, all options except :name can be specified without placing them in a hash, e.g.

t.integer :author_id, on_delete: :cascade
t.integer :author_id, references: nil

The foreign key behavior can be configured globally (see Config) or per-table (see create_table).

To examine your foreign key constraints, connection.foreign_keys returns a list of foreign key constraints defined for a given table, and connection.reverse_foreign_keys returns a list of foreign key constraints that reference a given table. See SchemaPlus::ActiveRecord::ConnectionAdapters::ForeignKeyDefinition.


SchemaPlus provides support for creating and dropping views. In a migration, a view can be created using a rails relation or literal sql:

create_view :posts_commented_by_staff,  Post.joins(comment: user).where(users: {role: 'staff'}).uniq
create_view :uncommented_posts,        "SELECT * FROM posts LEFT OUTER JOIN comments ON comments.post_id = WHERE IS NULL"

And can be dropped:

drop_view :posts_commented_by_staff
drop_view :uncommented_posts

ActiveRecord works with views the same as with ordinary tables. That is, for the above views you can define

class PostCommentedByStaff < ActiveRecord::Base
  table_name = "posts_commented_by_staff"

class UncommentedPost < ActiveRecord::Base

Column Defaults: Expressions

SchemaPlus allows defaults to be set using expressions or constant values:

t.datetime :seen_at, default: { expr: 'NOW()' }
t.datetime :seen_at, default: { value: "2011-12-11 00:00:00" }

Note that in MySQL only the TIMESTAMP column data type accepts SQL column defaults and Rails uses DATETIME, so expressions can't be used with MySQL.

The standard syntax will still work as usual:

t.datetime :seen_at, default: "2011-12-11 00:00:00"

Also, as a convenience

t.datetime :seen_at, default: :now

resolves to:

NOW()                 # PostgreSQL
(DATETIME('now'))     # SQLite3
invalid               # MySQL

Column Defaults: Using

SchemaPlus introduces a constant ActiveRecord::DB_DEFAULT that you can use to explicitly instruct the database to use the column default value (or expression). For example:

Post.create(category: ActiveRecord::DB_DEFAULT)
post.update_attributes(category: ActiveRecord::DB_DEFAULT)

(Without ActiveRecord::DB_DEFAULT, you can update a value to NULL but not to its default value.)

Note that after updating, you would need to reload a record to replace ActiveRecord::DB_DEFAULT with the value assigned by the database.

Note also that Sqlite3 does not support ActiveRecord::DB_DEFAULT; attempting to use it will raise ActiveRecord::StatementInvalid

Schema Dump and Load (schema.rb)

When dumping schema.rb, SchemaPlus orders the views and tables in the schema dump alphabetically, but subject to the requirement that each table or view be defined before those that depend on it. This allows all foreign key constraints to be defined within the scope of the table definition. (Unless there are cyclical dependencies, in which case some foreign keys constraints must be defined later.)

Also, when dumping schema.rb, SchemaPlus dumps explicit foreign key definition statements rather than relying on the auto-creation behavior, for maximum clarity and for independence from global config. And correspondingly, when loading a schema, i.e. with the context of ActiveRecord::Schema.define, SchemaPlus ensures that auto creation of foreign key constraints is turned off regardless of the global setting. But if for some reason you are creating your schema.rb file by hand, and would like to take advantage of auto-creation of foreign key constraints, you can re-enable it:

ActiveRecord::Schema.define do
    SchemaPlus.config.foreign_keys.auto_create = true
    SchemaPlus.config.foreign_keys.auto_index = true

    create_table ...etc...

Release notes:

master (to be released)


  • No longer support rails < 3.2 and ruby < 1.9

  • New feature: specify foreign key constraints using :foreign_key => { … }, motivated in particular to support :name (suggested by

  • New feature: create view using ActiveRecord relation

  • New feature: ActiveRecord::DB_DEFAULT (suggested by

  • New feature: renaming a table renames its indexes and constraints correspondingly.

  • Bug fix for postgres :kind index attribute (thanks to

  • Sort fks in dump for stability (thanks to

  • Bug fix: change_column should maintain foreign key constraints even when config.foreign_keys.auto_create is false

  • Bug fix: quote default expressions in schema dump (thanks to

  • Bug fix: when removing a foreign key constraint, remove its auto-generated index.

  • Bug fix: SchemaDumper.ignore_tables needs to support regexps (suggeste by

  • Bug fix: More robust handling of Postgresql schema_search path (suggested by

  • Bug fix: Only get index, view, and foreign key information from current schema (thanks to

Earlier releases

  • 0.4.1 - Bug fix: don't attempt foreign key creation for t.belongs_to … :polymorphic => true

  • 0.4.0 - Add :force for create_view (suggested by greglazarev). cleanups by betelgeuse

  • 0.3.4 - Bug fix: regression causing :default => false to be ignored

  • 0.3.3 - Bug fix: properly handle boolean defaults in mysql

  • 0.3.2 - Bug fix: make sure rake db:schema:load initializes schema_plus

  • 0.3.1 - Bug fix for PostgreSQL schema dump after change_column_default(… nil)

  • 0.3.0 - Add :default => expressions (Thanks to Luke Saunders). support rails 3.2 and ruby 1.9.3

  • 0.2.1 - Suppress duplicate add_indexes. compatibility with rails 3.2.0.rc2



SchemaPlus is tested using rspec and rvm, with some hackery to test against multiple versions of rails and ruby and db adapters. To run the tests, after you've forked & cloned: Make sure you have Postgresql and MySQL running. You'll need db users with permissions to create and access databases (schema_plus_test and schema_plus_test2). Default user is 'postgres' for Postgresql and 'schema_plus' for MySQL; you can change them via

$ export POSTGRES_DB_USER = pgusername
$ export MYSQL_DB_USER = mysqlusername


$ cd schema_plus
$ bundle install
$ rake create_databases
$ ./runspecs --install  # do this once, it runs 'bundle install' for all versions
$ ./runspecs # as many times as you like

See ./runspecs --help for more options. You can also manually pick a specific version of rails, ruby, and db to use, such as:

$ rvm use 1.9.2
$ export BUNDLE_GEMFILE=gemfiles/rails-3.2/Gemfile.sqlite3
$ bundle exec rake spec

Code coverage results will be in coverage/index.html – it should be at 100% coverage if you're running against all databases


This gem is released under the MIT license.