Module: DatabaseSlave::Relation

Defined in:
lib/database_slave/relation.rb

Instance Attribute Summary collapse

Instance Method Summary collapse

Instance Attribute Details

#slave_name ⇒ Object

Returns the value of attribute slave_name.



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# File 'lib/database_slave/relation.rb', line 3

def slave_name
  @slave_name
end

Instance Method Details

#calculate(operation, column_name, options = {}) ⇒ Object

Supports ActiveRecord::Calculations:

count, average, minimun, maximum, sum, calculate



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# File 'lib/database_slave/relation.rb', line 151

def calculate(operation, column_name, options = {})
  if !DatabaseSlave::RuntimeRegistry.current_slave_name
    begin
      DatabaseSlave::RuntimeRegistry.current_slave_name = slave_name if using_slave?
      super
    ensure
      DatabaseSlave::RuntimeRegistry.current_slave_name = nil
    end
  else
    super
  end
end

#except(*skips) ⇒ Object

junk hack:

except

这里hack一下添加进来.

(


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# File 'lib/database_slave/relation.rb', line 168

def except(*skips)
  slave_name_snake = slave_name.to_s.underscore.split('/').last
  return super if slave_name_snake.blank?
  using_slave? ? super.using(slave_name_snake.to_sym) : super
end

#exists?(id = false) ⇒ Boolean

Supports ActiveRecord::FinderMethods:

exists?

Returns:

  • (Boolean) 


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# File 'lib/database_slave/relation.rb', line 119

def exists?(id = false)
  if !DatabaseSlave::RuntimeRegistry.current_slave_name
    begin
      DatabaseSlave::RuntimeRegistry.current_slave_name = slave_name if using_slave?
      super
    ensure
      DatabaseSlave::RuntimeRegistry.current_slave_name = nil
    end
  else
    super
  end
end

#initialize(klass, table) ⇒ Object 



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# File 'lib/database_slave/relation.rb', line 5

def initialize(klass, table)
  slave_name = nil
  if (slave = ActiveRecord::Relation.class_variable_get(:@@slave_block_given)).present?
    self.slave_name = slave
  end

  super
end

#pluck(column_name) ⇒ Object

Supports ActiveRecord::Calculations:

pluck



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# File 'lib/database_slave/relation.rb', line 135

def pluck(column_name)
  if !DatabaseSlave::RuntimeRegistry.current_slave_name
    begin
      DatabaseSlave::RuntimeRegistry.current_slave_name = slave_name if using_slave?
      super
    ensure
      DatabaseSlave::RuntimeRegistry.current_slave_name = nil
    end
  else
    super
  end
end

#to_a ⇒ Object

Description

Rails中所有的relation最后都是调用to_a后返回最终结果.

这里我们重写ActiveRecord::Relation的to_a方法只是为了做一件事:

对应到代码即:

DatabaseSlave::RuntimeRegistry.current_slave_name = nil



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# File 'lib/database_slave/relation.rb', line 77

def to_a
  # 该if语句的作用是: 确保在一条使用从库的查询中存在的其他先决条件的
  # 查询也使用从库。例如:
  #
  #   class Book < ActiveRecord::Base
  #     default_scope lambda { where(:tag_id => Tag.published.pluck(:id)) }
  #   end
  #
  # 当我们使用如下查询
  #
  #   Book.order('id DESC').limit(2).pluck(:id)
  #
  # 时, default_scope中的Tag需要被先查询出来. 为了Book和Tag的查询都使用从库,
  # 避免查询Tag后便释放了从库连接而导致Book的查询使用的还是主库. 故在这里
  # 加了条件判断: 如果父查询已经设置了使用从库, 那么内部的所有查询都使用从库,
  # 直到父查询返回.
  #
  # Supports ActiveRecord::QueryMethods:
  #   select, group, order, reorder, joins, where, having,
  #   limit, offset, uniq
  #
  # And ActiveRecord::FinderMethods:
  #   first, first!, last, last!, find, all
  #
  # And ActiveRecord::Batches:
  #   find_each, find_in_batches
  #
  if !DatabaseSlave::RuntimeRegistry.current_slave_name
    begin
      DatabaseSlave::RuntimeRegistry.current_slave_name = slave_name if using_slave?
      super
    ensure
      DatabaseSlave::RuntimeRegistry.current_slave_name = nil
    end
  else
    super
  end
end

#unusing_slave ⇒ Object 



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# File 'lib/database_slave/relation.rb', line 18

def unusing_slave
  slave_name = nil

  self
end

#using_slave(slave_name) ⇒ Object Also known as: using 



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# File 'lib/database_slave/relation.rb', line 24

def using_slave(slave_name)
  if Settings.using_slave
    if block_given?
      db_name = "DatabaseSlave::ConnectionHandler::#{slave_name.to_s.strip.camelize}"
      unless ActiveRecord::Base.slave_connections.include? db_name
        raise DatabaseSlave::SlaveConnectionNotExists,
          "#{slave_name} is not exists."
      end

      ActiveRecord::Relation.class_variable_set(:@@slave_block_given, db_name)
      DatabaseSlave::RuntimeRegistry.current_slave_name ||= db_name
      begin
        yield
      ensure
        ActiveRecord::Relation.class_variable_set(:@@slave_block_given, nil)
        DatabaseSlave::RuntimeRegistry.current_slave_name = nil
      end
    else
      # 不能使用抽象类级联式查询, 即不能使用ActiveRecord::Base.using().where()
      if self.name.eql? DatabaseSlave::NoneActiveRecord.name
        raise DatabaseSlave::AbstractClassWithoutBlockError,
          'a block must be given to abstract class, or you can use a specific class.'
      end

      self.slave_name = "DatabaseSlave::ConnectionHandler::#{slave_name.to_s.strip.camelize}"
      relation = clone

      if ActiveRecord::Base.slave_connections.include? self.slave_name
        relation
      else
        raise DatabaseSlave::SlaveConnectionNotExists,
          "#{slave_name} is not exists."
      end
    end
  else # using master database if Settings.using_slave == false or nil
    block_given? ? yield : clone
  end
end

#using_slave? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/database_slave/relation.rb', line 14

def using_slave?
  slave_name.to_s.present?
end