Rails 数据库表之间关系

一对一关系实例: one-to-one

Ruby代码

class Order < ActiveRecord::Base

has_one :paid_order,

:class_name =>"Order",

:foreign_key => "order_id",

:conditions => "paid_on is not null"

class Order < ActiveRecord::Base
has_one :paid_order,
:class_name =>"Order",
:foreign_key => "order_id",
:conditions => "paid_on is not null"

在表格上加order_id (表格名单数_id)

Ruby代码

class Invoice < ActiveRecord::Base

belongs_to :order

class Invoice < ActiveRecord::Base
belongs_to :order

可选参数:class_name, :foreign_key, order, :conditions

Ruby代码

:dependent => true #删除主表行时同时删除子行

自定义的order用法:

class Customer < ActiveRecord::Base

has_many :orders

has_one :most_recent_order,

:class_name => 'Order',

:order => 'created_at DESC'

end

:dependent => true #删除主表行时同时删除子行
自定义的order用法:
class Customer < ActiveRecord::Base
has_many :orders
has_one :most_recent_order,
:class_name => 'Order',
:order => 'created_at DESC'
end

主.从 将被保存

Ruby代码

an_invoice = Invoice.new(...)

order.invoice = an_invoice # invoice被保存

an_invoice = Invoice.new(...)
order.invoice = an_invoice # invoice被保存

从.主 将要手动保存

新增加的方法:

Ruby代码

product(force_reload=false)

product=(obj)

build_product(attributes={})

create_product(attributes={})

product(force_reload=false)
product=(obj)
build_product(attributes={})
create_product(attributes={})

一对多关系(one-to-many)

Ruby代码

class Order < ActiveRecord::Base

has_many :line_items

class Order < ActiveRecord::Base
has_many :line_items

可选参数除了上面的,还有:exclusively_dependent, :finder_sql,:counter_sql
:exclusively_dependent 在子行没有其它表格瓜葛的情况下使用, 加快处理速度.
:finder_sql的使用实例:

Ruby代码

class Order < ActiveRecord::Base

has_many :rails_line_items,

:class_name => "LineItem",

:finder_sql => "select l. * from line_items l, products p " +

" where l.product_id = p.id " +

" and p.title like '%rails%'"

end

class Order < ActiveRecord::Base
has_many :rails_line_items,
:class_name => "LineItem",
:finder_sql => "select l. * from line_items l, products p " +
" where l.product_id = p.id " +
" and p.title like '%rails%'"
end

order的用法:

Ruby代码

class Order < ActiveRecord::Base

has_many :line_items,

:order =>"quantity, unit_price DESC"

end

class Order < ActiveRecord::Base
has_many :line_items,
:order =>"quantity, unit_price DESC"
end

主.从 将被保存

Ruby代码

an_invoice = Invoice.new(...)

order.invoices <<an_invoice # invoice

class LineItem < ActiveRecord::Base

belongs_to :order

. . .

an_invoice = Invoice.new(...)
order.invoices <<an_invoice # invoice

class LineItem < ActiveRecord::Base
belongs_to :order
. . .

has_many后可以引用集合:

Ruby代码

order = Order.find(123)

total = 0.0

order.line_items.each do |li|

total += li.quantity * li.unit_price

end

order = Order.find(123)
total = 0.0
order.line_items.each do |li|
total += li.quantity * li.unit_price
end

新增加的方法:

Ruby代码

orders(force_reload=false)

orders <<order

orders.push(order1, ...)

orders.delete(order1, ...)

orders.clear

orders.find(options...)

orders.build(attributes={})

orders.create(attributes={})

orders(force_reload=false)
orders <<order
orders.push(order1, ...)
orders.delete(order1, ...)
orders.clear
orders.find(options...)
orders.build(attributes={})
orders.create(attributes={})

多对多关系(many-to-many):

Ruby代码

class Product < ActiveRecord::Base

has_and_belongs_to_many :categories

#. . .

class Category < ActiveRecord::Base

has_and_belongs_to_many :products

#. . .

class Product < ActiveRecord::Base
has_and_belongs_to_many :categories
#. . .
class Category < ActiveRecord::Base
has_and_belongs_to_many :products
#. . .

要创建一个中间表格:
categories_products
两表格名字复数形式相联, 排字母前后排序

表格内连关联键
略

预载子表
用:include将子表内容加入内存,提高查询速度, 但损耗内存:

Ruby代码

for post in Post.find(:all, :include => [:author, :comments])

puts "Post: #{post.title}"

puts "Written by: #{post.author.name}"

puts "Last comment on: #{post.comments.first.created_on}"

end

for post in Post.find(:all, :include => [:author, :comments])
puts "Post: #{post.title}"
puts "Written by: #{post.author.name}"
puts "Last comment on: #{post.comments.first.created_on}"
end

自动计算子表行数
belongs_to加参数:

Ruby代码

counter_cache => true

counter_cache => true

数据库加 子表格名(复数)_count 段, 并加 :default=>0参数.
然后用 .size可以读取子表行数.
刷新数据读法:

Ruby代码

product.line_items(:refresh).size