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ctran on 08/21/06

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

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foreign_key_migration.rb

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Add foreign key support for migration

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  1. module ForeignKeyMigration
  2.   module AbstractAdapter
  3.     # Add foreign-key constraints when creating tables. It uses SQL-92 syntax and as such should be
  4.     # compatible with most databases that support foreign-key constraints. By default, 
  5.     # the constraint is named "fk_table_a_on_table_b
  6.     # 
  7.     # ===== Examples
  8.     # Add a foreign key to movie_crews (person_id) that references people table (id)
  9.     #   add_foreign_key :movie_crews, :person_id, :people
  10.     # 
  11.     # Specify the referenced columns
  12.     #   add_foreign_key :movie_crews, :person_id, :people, :id
  13.     # 
  14.     # Multiple columns
  15.     #   add_foreign_key :movie_crews, [:person_id, :role], :people, [:id, :role]
  16.     # 
  17.     # Add a foreign key with a name
  18.     #   add_foreign_key :movie_crews, :person_id, :people, :id, :name => 'movie_crews_xref_people'
  19.     # 
  20.     def add_foreign_key(foreign_table_name, foreign_column_names, primary_table_name, primary_column_names = :id, options = {})
  21.       foreign_column_names = Array(foreign_column_names).join(", ")
  22.       primary_column_names = Array(primary_column_names).join(", ")
  23.       fk_name = options[:name] || fk_name(foreign_table_name, foreign_column_names, primary_table_name, primary_column_names)
  24.       execute "ALTER TABLE #{foreign_table_name} ADD CONSTRAINT #{fk_name} FOREIGN KEY (#{foreign_column_names}) REFERENCES #{primary_table_name} (#{primary_column_names})"
  25.     end
  26.  
  27.     # Remove a foreign key constraint
  28.     # 
  29.     # ==== Examples
  30.     # ===== Remove the fk 'fk_user_role_user' from 'users_roles' table
  31.     #   remove_foreign_key :users_roles, :fk_users_roles_user
  32.     #   
  33.     # ===== Remove the fk on comments (post_id) reference posts (id)
  34.     #   remove_foreign_key :comments, :post_id, :posts
  35.     #   
  36.     def remove_foreign_key(foreign_table_name, fk_name, primary_table_name = nil, primary_column_names = nil)
  37.       primary_column_names = :id unless primary_column_names
  38.       fk_name = fk_name(foreign_table_name, fk_name, primary_table_name, primary_column_names) if primary_table_name
  39.       execute "ALTER TABLE #{foreign_table_name.to_s} DROP FOREIGN KEY #{fk_name.to_s}"
  40.     end
  41.  
  42.     def fk_name(foreign_table_name, foreign_column_names, primary_table_name, primary_column_names)
  43.       "fk_#{foreign_table_name.to_s}_on_#{primary_table_name.to_s}"
  44.     end
  45.   end   
  46. end

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