写了个migration的工具类 对外键引用和多对多关系的创建进行支持

写了个migration的工具类 对外键引用和多对多关系的创建进行支持

module MigrationHelper
   # Add foreign key for migrations  
   # Usage:  
   # * /db/migrate/xxxx_create_users.rb  
   # class CreateUsers < ActiveRecord::Migration  
   #   extend MigrateionHelpers  
   #   def self.up  
   #     ...  
   #     create_foreign_key :users, :group_id, :groups  
   #   end  
   #   def down.up  
   #     ...  
   #     drop_foreign_key  :users, :group_id  
   #   end  
   # end  
   #    
  def create_foreign_key(from_table, from_column, to_table, to_column='id')
    execute %(alter table #{from_table}
              add constraint #{constraint_name(from_table, from_column)}
              foreign key (#{from_column})
              references #{to_table}(#{to_column}))
  end
  
  def drop_foreign_key(from_table, from_column)    
    execute %(alter table #{from_table} 
              drop constraint #{constraint_name(from_table, from_column)})
  end
  
  def constraint_name(table, column)
    "fk_#{table}_#{column}"
  end
  

   # Add many-to-many relationship for migrations  
   # Usage:  
   # * /db/migrate/xxxx_create_users.rb  
   # class CreateUsers < ActiveRecord::Migration  
   #   extend MigrateionHelpers  
   #   def self.up  
   #     ...  
   #   end  
   #   def down.up  
   #     ...  
   #   end  
   # end  
   # * /db/migrate/xxxx_create_groups.rb  
   # class CreateGroups < ActiveRecord::Migration  
   #   extend MigrateionHelpers  
   #   def self.up  
   #     ...  
   #     create_many_to_many :users, :groups
   #   end  
   #   def down.up  
   #     ...  
   #     drop_many_to_many :users, :groups
   #   end  
   # end  
   #      
  def create_many_to_many(table1, table2)
    @table = many_to_many_name(table1, table2)
    @column1 = table1.to_s.singularize + "_id"
    @column2 = table2.to_s.singularize + "_id"
    create_table @table, :id => false do |t|
      t.integer @column1
      t.integer @column2
    end
    
    create_foreign_key @table, @column1, table1
    create_foreign_key @table, @column2, table2  
  end

  def drop_many_to_many(table1, table2)
    @table = many_to_many_name(table1, table2)
    @column1 = table1.to_s.singularize + "_id"
    @column2 = table2.to_s.singularize + "_id"
    
    drop_foreign_key @table, @column1
    drop_foreign_key @table, @column2

    drop_table @table
  end
  
  def many_to_many_name(table1, table2)
    "#{table1}_#{table2}"
  end

end