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遷移指令記錄器

ActiveRecord::Migration::CommandRecorder 記錄在遷移期間執行的指令，並知道如何還原這些指令。 CommandRecorder 知道如何反轉下列指令

  • add_column

  • add_foreign_key

  • add_check_constraint

  • add_exclusion_constraint

  • add_unique_constraint

  • add_index

  • add_reference

  • add_timestamps

  • change_column_default (必須提供 :from 和 :to 選項)

  • change_column_null

  • change_column_comment (必須提供 :from 和 :to 選項)

  • change_table_comment (必須提供 :from 和 :to 選項)

  • create_enum

  • create_join_table

  • create_virtual_table

  • create_table

  • disable_extension

  • drop_enum (必須提供值的清單)

  • drop_join_table

  • drop_virtual_table (必須提供選項)

  • drop_table (必須提供區塊)

  • enable_extension

  • remove_column (必須提供類型)

  • remove_columns (必須提供類型 :type 選項)

  • remove_foreign_key (必須提供第二個表格)

  • remove_check_constraint

  • remove_exclusion_constraint

  • remove_unique_constraint

  • remove_index

  • remove_reference

  • remove_timestamps

  • rename_column

  • rename_enum

  • rename_enum_value (必須提供 :from 和 :to 選項)

  • rename_index

  • rename_table

方法
I
N
R

常數

ReversibleAndIrreversibleMethods = [ :create_table, :create_join_table, :rename_table, :add_column, :remove_column, :rename_index, :rename_column, :add_index, :remove_index, :add_timestamps, :remove_timestamps, :change_column_default, :add_reference, :remove_reference, :transaction, :drop_join_table, :drop_table, :execute_block, :enable_extension, :disable_extension, :change_column, :execute, :remove_columns, :change_column_null, :add_foreign_key, :remove_foreign_key, :change_column_comment, :change_table_comment, :add_check_constraint, :remove_check_constraint, :add_exclusion_constraint, :remove_exclusion_constraint, :add_unique_constraint, :remove_unique_constraint, :create_enum, :drop_enum, :rename_enum, :add_enum_value, :rename_enum_value, :create_schema, :drop_schema, :create_virtual_table, :drop_virtual_table ]
 

屬性

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

類別公用方法

new(delegate = nil)

來源： 顯示 | 在 GitHub 上

# File activerecord/lib/active_record/migration/command_recorder.rb, line 67
def initialize(delegate = nil)
  @commands = []
  @delegate = delegate
  @reverting = false
end

執行個體公用方法

inverse_of(command, args, &block)

傳回給定指令的反向指令。例如

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

如果指令的反向指令需要多個指令，傳回指令陣列。

recorder.inverse_of(:remove_columns, [:some_table, :foo, :bar, type: :string])
# => [[:add_column, :some_table, :foo, :string], [:add_column, :some_table, :bar, :string]]

如果此方法無法反轉 command，則會引發 IrreversibleMigration 例外。

來源：顯示 | 在 GitHub

# File activerecord/lib/active_record/migration/command_recorder.rb, line 114
      def inverse_of(command, args, &block)
        method = :"invert_#{command}"
        raise IrreversibleMigration, <<~MSG unless respond_to?(method, true)
          This migration uses #{command}, which is not automatically reversible.
          To make the migration reversible you can either:
          1. Define #up and #down methods in place of the #change method.
          2. Use the #reversible method to define reversible behavior.
        MSG
        send(method, args, &block)
      end

record(*command, &block)

記錄命令。命令應該是方法名稱和參數。例如

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

來源：顯示 | 在 GitHub

# File activerecord/lib/active_record/migration/command_recorder.rb, line 94
def record(*command, &block)
  if @reverting
    @commands << inverse_of(*command, &block)
  else
    @commands << (command << block)
  end
end

replay(migration)

來源：顯示 | 在 GitHub

# File activerecord/lib/active_record/migration/command_recorder.rb, line 148
def replay(migration)
  commands.each do |cmd, args, block|
    migration.send(cmd, *args, &block)
  end
end

revert()

在執行提供的區段時，將會進入還原模式。所有記錄的命令最終會被記錄為還原和以相反順序。例如

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

來源：顯示 | 在 GitHub

# File activerecord/lib/active_record/migration/command_recorder.rb, line 80
def revert
  @reverting = !@reverting
  previous = @commands
  @commands = []
  yield
ensure
  @commands = previous.concat(@commands.reverse)
  @reverting = !@reverting
end