Rails 6 ActiveRecord::Base.configurations

Rails 6 changed the return value of ActiveRecord::Base.configurations to an object of ActiveRecord::DatabaseConfigurations. Before Rails 6, ActiveRecord::Base.configurations returned a hash with all the database configurations. We can call to_h on the object of ActiveRecord::DatabaseConfigurations to get a hash.

A method named configs_for has also been added on to fetch configurations for a particular environment.

Rails 5.2

1>> ActiveRecord::Base.configurations
2
3=> {"development"=>{"adapter"=>"sqlite3", "pool"=>5, "timeout"=>5000, "database"=>"db/development.sqlite3"}, "test"=>{"adapter"=>"sqlite3", "pool"=>5, "timeout"=>5000, "database"=>"db/test.sqlite3"}, "production"=>{"adapter"=>"sqlite3", "pool"=>5, "timeout"=>5000, "database"=>"db/production.sqlite3"}}
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Rails 6.0.0.beta2

1>> ActiveRecord::Base.configurations
2
3=> #<ActiveRecord::DatabaseConfigurations:0x00007fc18274f9f0 @configurations=[#<ActiveRecord::DatabaseConfigurations::HashConfig:0x00007fc18274f680 @env_name="development", @spec_name="primary", @config={"adapter"=>"sqlite3", "pool"=>5, "timeout"=>5000, "database"=>"db/development.sqlite3"}>, #<ActiveRecord::DatabaseConfigurations::HashConfig:0x00007fc18274f608 @env_name="test", @spec_name="primary", @config={"adapter"=>"sqlite3", "pool"=>5, "timeout"=>5000, "database"=>"db/test.sqlite3"}>, #<ActiveRecord::DatabaseConfigurations::HashConfig:0x00007fc18274f590 @env_name="production", @spec_name="primary", @config={"adapter"=>"sqlite3", "pool"=>5, "timeout"=>5000, "database"=>"db/production.sqlite3"}>]>
4
5>> ActiveRecord::Base.configurations.to_h
6
7=> {"development"=>{"adapter"=>"sqlite3", "pool"=>5, "timeout"=>5000, "database"=>"db/development.sqlite3"}, "test"=>{"adapter"=>"sqlite3", "pool"=>5, "timeout"=>5000, "database"=>"db/test.sqlite3"}, "production"=>{"adapter"=>"sqlite3", "pool"=>5, "timeout"=>5000, "database"=>"db/production.sqlite3"}}
8
9>> ActiveRecord::Base.configurations['development']
10
11=> {"adapter"=>"sqlite3", "pool"=>5, "timeout"=>5000, "database"=>"db/development.sqlite3"}
12
13>> ActiveRecord::Base.configurations.configs_for(env_name: "development")
14
15=> [#<ActiveRecord::DatabaseConfigurations::HashConfig:0x00007fc18274f680 @env_name="development", @spec_name="primary", @config={"adapter"=>"sqlite3", "pool"=>5, "timeout"=>5000, "database"=>"db/development.sqlite3"}>]
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Here is the relevant pull request.