Rails 6.1 creates abstract classes in multiple database mode

Rails started supporting multiple databases from Rails 6.0. To use a specific database, we can specify the database connection in the model using connects_to. In the following case we want Person model to connect to crm database.

1
2class Person < ApplicationRecord
3connects_to database: { writing: :crm }
4end
5
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As the application grows, more and more models start sharing the same database. Now a lot of models may contain connects_to call to the same database.

1class Person < ApplicationRecord
2connects_to database: { writing: :crm }
3end
4
5class Order < ApplicationRecord
6connects_to database: { writing: :crm }
7end
8
9class Sale < ApplicationRecord
10connects_to database: { writing: :crm }
11end
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In order to avoid the duplication, we can create an abstract class connecting to a database and manually inherit all other models from that class. This could look like this.

1class CrmRecord < ApplicationRecord
2self.abstract_class = true
3
4connects_to database: { writing: :crm }
5end
6
7class Person < CrmRecord
8end
9
10class Order < CrmRecord
11end
12
13class Sale < CrmRecord
14end
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Rails 6.1

Before Rails 6.1 we had no choice but to create that abstract class manually. Rails 6.1 allows us to generate an abstract class when we are generating a model using scaffold.

1$ rails g scaffold Person name:string --database=crm
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It creates an abstract class with the database's name appended with Record. The generated model automatically inherits from the new abstract class.

1
2# app/models/users_record.rb
3
4class CrmRecord < ApplicationRecord
5self.abstract_class = true
6
7connects_to database: { writing: :crm }
8end
9
10# app/models/admin.rb
11
12class Person < CrmRecord
13end
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If the abstract class already exists, it is not created again. We can also use an existing class as the abstract class by passing parent option to the scaffold command.

1$ rails g scaffold Customer name:string --database=crm --parent=PrimaryRecord
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This skips generating CrmRecord class as we have specified Rails to use PrimaryRecord abstract class as its parent.

Check out the pull request for more details on this.