Posted By

ctran on 08/21/06

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rails

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Last Edited at 08/21/06 12:26am

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foreign_key_migration.rb

/ Published in: Ruby

Add foreign key support for migration

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module ForeignKeyMigration
  module AbstractAdapter
    # Add foreign-key constraints when creating tables. It uses SQL-92 syntax and as such should be
    # compatible with most databases that support foreign-key constraints. By default, 
    # the constraint is named "fk_table_a_on_table_b
    # 
    # ===== Examples
    # Add a foreign key to movie_crews (person_id) that references people table (id)
    #   add_foreign_key :movie_crews, :person_id, :people
    # 
    # Specify the referenced columns
    #   add_foreign_key :movie_crews, :person_id, :people, :id
    # 
    # Multiple columns
    #   add_foreign_key :movie_crews, [:person_id, :role], :people, [:id, :role]
    # 
    # Add a foreign key with a name
    #   add_foreign_key :movie_crews, :person_id, :people, :id, :name => 'movie_crews_xref_people'
    # 
    def add_foreign_key(foreign_table_name, foreign_column_names, primary_table_name, primary_column_names = :id, options = {})
      foreign_column_names = Array(foreign_column_names).join(", ")
      primary_column_names = Array(primary_column_names).join(", ")
      fk_name = options[:name] || fk_name(foreign_table_name, foreign_column_names, primary_table_name, primary_column_names)
      execute "ALTER TABLE #{foreign_table_name} ADD CONSTRAINT #{fk_name} FOREIGN KEY (#{foreign_column_names}) REFERENCES #{primary_table_name} (#{primary_column_names})"
    end
    
    # Remove a foreign key constraint
    # 
    # ==== Examples
    # ===== Remove the fk 'fk_user_role_user' from 'users_roles' table
    #   remove_foreign_key :users_roles, :fk_users_roles_user
    #   
    # ===== Remove the fk on comments (post_id) reference posts (id)
    #   remove_foreign_key :comments, :post_id, :posts
    #   
    def remove_foreign_key(foreign_table_name, fk_name, primary_table_name = nil, primary_column_names = nil)
      primary_column_names = :id unless primary_column_names
      fk_name = fk_name(foreign_table_name, fk_name, primary_table_name, primary_column_names) if primary_table_name
      execute "ALTER TABLE #{foreign_table_name.to_s} DROP FOREIGN KEY #{fk_name.to_s}"
    end
    
    def fk_name(foreign_table_name, foreign_column_names, primary_table_name, primary_column_names)
      "fk_#{foreign_table_name.to_s}_on_#{primary_table_name.to_s}"
    end
  end   
end

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