Question

I want to create migrations to add columns from my rails application (not through rails g migration xxxx), while creating the migration I want to store the version number to the for the migration for later possible down operation.

The scenario is, I have an application with generalized tables and their fields. The application can be deployed for multiple customers. I want to provide a way to define custom fields in the table. Once the user selects/inputs desired data like table_name, field_name, data_type etc. I will be creating a new migration to add the field and store the version number somewhere in the database. This version number will be used to migrate:down in case the user decides to delete the field.

Is there any other better approach than this?

Answer 1

I have implemented this as below:
Depending upon the field_name and table_name I create a migration using:

def create_migration
    field_name_for_db = field_name.gsub(' ', '_').downcase
    migration_name = "add_column_#{self.field_name}_to_#{self.table_name}"
    logger.info "cd #{Rails.root} && rails g migration #{migration_name} #{self.field_name}:string > #{Rails.root}/tmp/migration_details.txt && rake db:migrate"
    system "cd #{Rails.root} && rails g migration #{migration_name} #{self.field_name}:string > #{Rails.root}/tmp/migration_details.txt && rake db:migrate"
    migration_version = File.read("#{Rails.root}/tmp/migration_details.txt").split('/').last.split("_#{migration_name}").first
    self.migration_name = migration_name
    self.migration_version = migration_version
    self.save
  end

In this method I have redirected the output of create migration command to a file and retrieving migration number from the file and then storing it to the database.