class ActiveRecord::Migration::CommandRecorder - activerecord-4.2.5.2 Documentation

# class ActiveRecord::Migration::CommandRecorder

`ActiveRecord::Migration::CommandRecorder` records commands done during a migration and knows how to reverse those commands. The CommandRecorder knows how to invert the following commands:

- add_column

- add_index

- add_timestamps

- create_table

- create_join_table

- remove_timestamps

- rename_column

- rename_index

- rename_table

### Attributes

commands[RW]
delegate[RW]
reverting[RW]

### Public Class Methods

new(delegate = nil) click to toggle source

    # File lib/active_record/migration/command_recorder.rb, line 21
    def initialize(delegate = nil)
      @commands = []
      @delegate = delegate
      @reverting = false
    end

### Public Instance Methods

inverse_of(command, args, &block) click to toggle source

Returns the inverse of the given command. For example:

    recorder.inverse_of(:rename_table, [:old, :new])
    # => [:rename_table, [:new, :old]]

This method will raise an `IrreversibleMigration` exception if it cannot invert the `command`.

    # File lib/active_record/migration/command_recorder.rb, line 63
    def inverse_of(command, args, &block)
      method = :"invert_#{command}"
      raise IrreversibleMigration unless respond_to?(method, true)
      send(method, args, &block)
    end

record(*command, &block) click to toggle source

record `command`. `command` should be a method name and arguments. For example:

    recorder.record(:method_name, [:arg1, :arg2])

    # File lib/active_record/migration/command_recorder.rb, line 48
    def record(*command, &block)
      if @reverting
        @commands << inverse_of(*command, &block)
      else
        @commands << (command << block)
      end
    end

revert() { || ... } click to toggle source

While executing the given block, the recorded will be in reverting mode. All commands recorded will end up being recorded reverted and in reverse order. For example:

    recorder.revert{ recorder.record(:rename_table, [:old, :new]) }
    # same effect as recorder.record(:rename_table, [:new, :old])

    # File lib/active_record/migration/command_recorder.rb, line 34
    def revert
      @reverting = !@reverting
      previous = @commands
      @commands = []
      yield
    ensure
      @commands = previous.concat(@commands.reverse)
      @reverting = !@reverting
    end

### Private Instance Methods

invert_add_foreign_key(args) click to toggle source

    # File lib/active_record/migration/command_recorder.rb, line 172
    def invert_add_foreign_key(args)
      from_table, to_table, add_options = args
      add_options ||= {}

      if add_options[:name]
        options = { name: add_options[:name] }
      elsif add_options[:column]
        options = { column: add_options[:column] }
      else
        options = to_table
      end

      [:remove_foreign_key, [from_table, options]]
    end

invert_add_index(args) click to toggle source

    # File lib/active_record/migration/command_recorder.rb, line 143
    def invert_add_index(args)
      table, columns, options = *args
      options ||= {}

      index_name = options[:name]
      options_hash = index_name ? { name: index_name } : { column: columns }

      [:remove_index, [table, options_hash]]
    end

invert_change_column_null(args) click to toggle source

    # File lib/active_record/migration/command_recorder.rb, line 167
    def invert_change_column_null(args)
      args[2] = !args[2]
      [:change_column_null, args]
    end

invert_drop_table(args, &block) click to toggle source
Calls superclass method

    # File lib/active_record/migration/command_recorder.rb, line 119
    def invert_drop_table(args, &block)
      if args.size == 1 && block == nil
        raise ActiveRecord::IrreversibleMigration, "To avoid mistakes, drop_table is only reversible if given options or a block (can be empty)."
      end
      super
    end

invert_remove_column(args) click to toggle source
Calls superclass method

    # File lib/active_record/migration/command_recorder.rb, line 130
    def invert_remove_column(args)
      raise ActiveRecord::IrreversibleMigration, "remove_column is only reversible if given a type." if args.size <= 2
      super
    end

invert_remove_index(args) click to toggle source

    # File lib/active_record/migration/command_recorder.rb, line 153
    def invert_remove_index(args)
      table, options = *args

      unless options && options.is_a?(Hash) && options[:column]
        raise ActiveRecord::IrreversibleMigration, "remove_index is only reversible if given a :column option."
      end

      options = options.dup
      [:add_index, [table, options.delete(:column), options]]
    end

invert_rename_column(args) click to toggle source

    # File lib/active_record/migration/command_recorder.rb, line 139
    def invert_rename_column(args)
      [:rename_column, [args.first] + args.last(2).reverse]
    end

invert_rename_index(args) click to toggle source

    # File lib/active_record/migration/command_recorder.rb, line 135
    def invert_rename_index(args)
      [:rename_index, [args.first] + args.last(2).reverse]
    end

invert_rename_table(args) click to toggle source

    # File lib/active_record/migration/command_recorder.rb, line 126
    def invert_rename_table(args)
      [:rename_table, args.reverse]
    end

method_missing(method, *args, &block) click to toggle source

Forwards any missing method call to the target.

Calls superclass method

    # File lib/active_record/migration/command_recorder.rb, line 188
    def method_missing(method, *args, &block)
      if @delegate.respond_to?(method)
        @delegate.send(method, *args, &block)
      else
        super
      end
    end