活动记录模型的动态表名

DB表分区实际上是非常常见的实践。如果有人以前没做过,我会很惊讶的。行动可分割如何? http://revolutiononrails.blogspot.com/2007/04/plugin-release-actsaspartitionable.html

另一种可能性是:DBMS可以假设分区是一个大表吗?我认为MySQL支持这个。

这是一个你能做到的方法。基本(70行代码之前)是:

• 为每种车型创建一个has_many
• 定义一个方法“wheels”,该方法使用关联中的表名来获取正确的控制盘

#!/usr/bin/env ruby
%w|rubygems active_record irb|.each {|lib| require lib}
ActiveSupport::Inflector.inflections.singular("toyota", "toyota")
CAR_TYPES = %w|ford buick toyota|

ActiveRecord::Base.logger = Logger.new(STDOUT)
ActiveRecord::Base.establish_connection(
  :adapter => "sqlite3",
  :database => ":memory:"
)

ActiveRecord::Schema.define do
  create_table :cars do |t|
    t.string :name
  end

  create_table :car_to_wheel_table_map, :id => false do |t|
    t.integer :car_id
    t.string :wheel_table
  end

  CAR_TYPES.each do |car_type|
    create_table "wheels_for_#{car_type.pluralize}" do |t|
      t.integer :car_id
      t.string :color
    end
  end
end

CAR_TYPES.each do |car_type|
  eval <<-END
    class #{car_type.classify}Wheel < ActiveRecord::Base
      set_table_name "wheels_for_#{car_type.pluralize}"
      belongs_to :car
    end
  END
end

class Car < ActiveRecord::Base
  has_one :car_wheel_map

  CAR_TYPES.each do |car_type|
    has_many "#{car_type}_wheels"
  end

  delegate :wheel_table, :to => :car_wheel_map

  def wheels
    send("#{wheel_table}_wheels")
  end
end

class CarWheelMap < ActiveRecord::Base
  set_table_name "car_to_wheel_table_map"
  belongs_to :car
end


rav4 = Car.create(:name => "Rav4")
rav4.create_car_wheel_map(:wheel_table => "toyota")
rav4.wheels.create(:color => "red")

fiesta = Car.create(:name => "Fiesta")
fiesta.create_car_wheel_map(:wheel_table => "ford")
fiesta.wheels.create(:color => "green")

IRB.start if __FILE__ == $0

不如这样吧?(要点如下: http://gist.github.com/111041

#!/usr/bin/env ruby
%w|rubygems active_record irb|.each {|lib| require lib}
ActiveSupport::Inflector.inflections.singular("toyota", "toyota")

ActiveRecord::Base.logger = Logger.new(STDOUT)
ActiveRecord::Base.establish_connection(
  :adapter => "sqlite3",
  :database => ":memory:"
)

ActiveRecord::Schema.define do
  create_table :cars do |t|
    t.string :name
  end

  create_table :car_to_wheel_table_map, :id => false do |t|
    t.integer :car_id
    t.string :wheel_table
  end

  create_table :wheels_for_fords do |t|
    t.integer :car_id
    t.string :color
  end

  create_table :wheels_for_toyotas do |t|
    t.integer :car_id
    t.string :color
  end
end

class Wheel < ActiveRecord::Base
  set_table_name nil
  belongs_to :car
end

class CarWheelMap < ActiveRecord::Base
  set_table_name "car_to_wheel_table_map"
  belongs_to :car
end

class Car < ActiveRecord::Base
  has_one :car_wheel_map
  delegate :wheel_table, :to => :car_wheel_map

  def wheels
    @wheels ||= begin
      the_klass = "#{wheel_table.classify}Wheel"
      eval <<-END
        class #{the_klass} < ActiveRecord::Base
          set_table_name "wheels_for_#{wheel_table.pluralize}"
          belongs_to :car
        end
      END

      self.class.send(:has_many, "#{wheel_table}_wheels")
      send "#{wheel_table}_wheels"
    end
  end
end

rav4 = Car.create(:name => "Rav4")
rav4.create_car_wheel_map(:wheel_table => "toyota")

fiesta = Car.create(:name => "Fiesta")
fiesta.create_car_wheel_map(:wheel_table => "ford")

rav4.wheels.create(:color => "red")
fiesta.wheels.create(:color => "green")

# IRB.start if __FILE__ == $0

我将与模型中的自定义函数进行关联:

has_one :cat_to_wheel_table_map

def wheels
  Wheel.find_by_sql("SELECT * FROM #{cat_to_wheel_table_map.wheel_table} WHERE car_id == #{id}")
end

也许您可以使用association with:finder_sql来完成,但我不确定如何向它传递参数。我使用了model Wheel,如果您希望通过ActiveRecord映射数据,则必须定义它。也许你可以从你现有的一个表格中用车轮做这个模型。

可悲的是,我知道你的烦恼。谁想在你的数据库中划分表,一定是被你老板炒了鱿鱼,被我雇了;-)

无论如何,解决方案(通过RailsForum): http://railsforum.com/viewtopic.php?id=674

干杯

假设1:你知道你在看什么类型的车,这样你就可以判断它是福特还是道奇。

稍后您应该将其规范化,但现在让我们保持简单。

CREATE TABLE cars (
  `id` int(11) NOT NULL auto_increment,
  `name` varchar(255),
  'make' varchar(255),
  #ect
)


class Wheel < ActiveRecord::Base
   def find_by_make(iMake)
       select("wheels_for_#{iMake}.*").from("wheels_for_#{iMake}");
   end
 #...
end

你可以在里面添加一些保护来验证和关闭你的iMake。 您还可以做一些事情来确保您的表存在。

现在给桌子写信。。我不知道那会怎样。我只看过这本书。

为什么不干脆把所有的轮子放在一张桌子上,用一个标准:有很多吗?您可以在迁移中执行此操作:

1. 创建新的控制盘表