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ruby find_each for permance

ruby find_each for permance

find_each (options = {}) public

Yields each record that was found by the find options . The find is performed by find_in_batches with a batch size of 1000 (or as specified by the :batch_size option).

Example: 

   Person . find_each (:conditions => "age > 21") do |person|
    person.party_all_night!
  end

Note: This method is only intended to use for batch processing of large amounts of records that wouldn’t fit in memory all at once. If you just need to loop over less than 1000 records, it’s probably better just to use the regular find methods

reference:

http://apidock.com/rails/ActiveRecord/Batches/ClassMethods/find_each

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2009-07-31

rails查询学习笔记

教程原文 http://guides.rubyonrails.org/active_record_querying.html
1、获取数据
.获取第一条、最后一条记录

Ruby代码

Model.first    Model.first(options)    Model.find(:first, options)    Model.last    Model.last(options)    Model.find(:last, options)  
Model.first
Model.first(options)
Model.find(:first, options)

Model.last
Model.last(options)
Model.find(:last, options)

.通过id获取记录

Ruby代码

Model.find(1, 10, options)    Model.find([1, 10], options)  
Model.find(1, 10, options)
Model.find([1, 10], options)

.find all

Ruby代码

Model.all(options)  
Model.all(options)

.对一组数据进行相同操作

Ruby代码

User.all.each do |user|        NewsLetter.weekly_deliver(user)    end 
User.all.each do |user|
	NewsLetter.weekly_deliver(user)
end

如果表记录数比较大，这种方式比较耗资源，因为它会一次载入整个表的数据。改用以下这种方式，它每次只载入1000行，然后逐步yield完整个表

Ruby代码

User.find_each do |user|        NewsLetter.weekly_deliver(user)    end 
User.find_each do |user|
	NewsLetter.weekly_deliver(user)
end

自定义方式，find_each接受和find同样的options

Ruby代码

User.find_each(:batch_size => 5000, :start => 2000) do |user|        NewsLetter.weekly_deliver(user)    end 
User.find_each(:batch_size => 5000, :start => 2000) do |user|
	NewsLetter.weekly_deliver(user)
end

find_in_batches，和find_each相似，但它yield时传递的是model对象数组，而不是单个model对象

Ruby代码

Invoice.find_in_batches(:include => :invoice_lines) do |invoices|        export.add_invoices(invoices)    end 
Invoice.find_in_batches(:include => :invoice_lines) do |invoices|
	export.add_invoices(invoices)
end

2、查询条件
通过替换？来传递条件值，可避免SQL注入

Ruby代码

Client.first(:conditions => ["orders_count = ?", params[:orders])  
Client.first(:conditions => ["orders_count = ?", params[:orders])

symbol占位条件

Ruby代码

Client.all(:conditions => ["created_at >= :start_date AND created_at <= :end_date", {:start_date => params[:start_date], :end_date => params[:end_date] }])  
Client.all(:conditions => ["created_at >= :start_date AND created_at <= :end_date", {:start_date => params[:start_date], :end_date => params[:end_date] }])

范围条件 in(集合)

Ruby代码

Client.all(:conditions => ["created_at IN (?)", (params[:start_date].to_date)..(params[:end_date].to_date])  
Client.all(:conditions => ["created_at IN (?)", (params[:start_date].to_date)..(params[:end_date].to_date])

生成sql

Sql代码

SELECT * FROM users WHERE (created_at IN ('2007-12-31','2008-01-01','2008-01-02','2008-01-03','2008-01-04','2008-01-05', '2008-01-06','2008-01-07','2008-01-08'))  
SELECT * FROM users WHERE (created_at IN ('2007-12-31','2008-01-01','2008-01-02','2008-01-03','2008-01-04','2008-01-05', '2008-01-06','2008-01-07','2008-01-08'))

如果要生成日期时间，再加上.to_time
params[:start_date].to_date.to_time，生成2007-12-01 0格式
有上数据库会在以上条件中报错，如Mysql会报查询语句过长的错误，此时可以改成created_at > ? AND created_at < ?的形式
Hash条件

Ruby代码

Client.all(:conditions => {:locked => true })   
Client.all(:conditions => {:locked => true })

带范围条件

Ruby代码

Client.all(:conditons => {:created => (Time.now.midnight - 1.day)..Time.now.midnight})  
Client.all(:conditons => {:created => (Time.now.midnight - 1.day)..Time.now.midnight})

生成sql

Sql代码

SELECT * FROM clients WHERE (clients.created_at BETWEEN '2008-12-21 0' AND '2008-12-22 0')  
SELECT * FROM clients WHERE (clients.created_at BETWEEN '2008-12-21 0' AND '2008-12-22 0')

集合条件

Ruby代码

Client.all(:conditons => {:orders_count => [1,3,5])  
Client.all(:conditons => {:orders_count => [1,3,5])

生成sql

Sql代码

SELECT * FROM clients WHERE (clients.orders_count IN (1,3,5))   
SELECT * FROM clients WHERE (clients.orders_count IN (1,3,5))

3、查询选项
排序

Ruby代码

#单个排序 Client.all(:order => "created_at ASC")    #多个排序 Client.all(:order => "orders_count ASC, created_at DESC")  
#单个排序
Client.all(:order => "created_at ASC")
#多个排序
Client.all(:order => "orders_count ASC, created_at DESC")

返回指定字段

Ruby代码

Client.all(:select => "viewable_by, locked")    #使用函数 Client.all(:select => "DISTINCT(name)")  
Client.all(:select => "viewable_by, locked")
#使用函数
Client.all(:select => "DISTINCT(name)")

限定和偏移Limit and Offset

Ruby代码

Client.all(:limit => 5)    #生成 SELECT * FROM clients LIMIT 5    Client.all(:limit => 5, :offset => 5)    #生成 SELECT * FROM clients LIMIT 5, 5  
Client.all(:limit => 5)
#生成
SELECT * FROM clients LIMIT 5
Client.all(:limit => 5, :offset => 5)
#生成
SELECT * FROM clients LIMIT 5, 5

Group分组

Ruby代码

Order.all(:group => "date(created_at)", :order => "created_at")  
Order.all(:group => "date(created_at)", :order => "created_at")

生成sql

Sql代码

SELECT * FROM orders GROUP BY date(created_at)  
SELECT * FROM orders GROUP BY date(created_at)

Having

Ruby代码

Order.all(:group => "date(created_at)", :having => ["created_at > ?", 1.month.ago)  
Order.all(:group => "date(created_at)", :having => ["created_at > ?", 1.month.ago)

生成sql

Sql代码

SELECT * FROM orders GROUP BY date(created_at) HAVING created_at > '2009-01-15' 
SELECT * FROM orders GROUP BY date(created_at) HAVING created_at > '2009-01-15'

只读

Ruby代码

client = Client.first(:readonly => true)    client.locked = false client.save    #对只读对象进行保存将会触发ActiveRecord::ReadOnlyRecord异常 
client = Client.first(:readonly => true)
client.locked = false
client.save
#对只读对象进行保存将会触发ActiveRecord::ReadOnlyRecord异常

更新时锁定记录
乐观锁Optimistic Locking
为使用乐观锁，须在表里建一个lock_version的字段，每次更新记录时，ActiveRecord自动递增lock_version的值，

Ruby代码

c1 = Client.find(1) c2 = Client.find(1) c1.name = "Michael" c1.save c2.name = "should fail" c2.save # Raises a ActiveRecord::StaleObjectError 
c1 = Client.find(1) c2 = Client.find(1) c1.name = "Michael" c1.save c2.name = "should fail" c2.save # Raises a ActiveRecord::StaleObjectError

备注：You must ensure that your database schema defaults the lock_version column to 0.
This behavior can be turned off by setting ActiveRecord::Base.lock_optimistically = false.
指定乐观锁字段名

Ruby代码

class Client < ActiveRecord::Base set_locking_column :lock_client_column end 
class Client < ActiveRecord::Base set_locking_column :lock_client_column end

悲观锁Pessimistic Locking
悲观锁定由数据库直接提供

Ruby代码

Item.transaction do     i = Item.first(:lock => true)        i.name = 'Jones'     i.save    end 
Item.transaction do 
	i = Item.first(:lock => true)
	i.name = 'Jones'
	i.save
end

Mysql执行返回
SQL (0.2ms) BEGIN Item Load (0.3ms) SELECT * FROM `items` LIMIT 1 FOR UPDATE Item Update (0.4ms) UPDATE `items` SET `updated_at` = '2009-02-07 18:05:56', `name` = 'Jones' WHERE `id` = 1 SQL (0.8ms) COMMIT
为特定数据库加入原始的lock声明
为Mysql的锁定声明为共享模式，即锁定时仍然可读
Item.transaction do  i = Item.find(1, :lock => "LOCK IN SHARE MODE")  i.increment!(:views) end
4、关联表

Ruby代码

Client.all(:joins => "LEFT OUTER JOIN address ON addresses.client_id = clients.id')  
Client.all(:joins => "LEFT OUTER JOIN address ON addresses.client_id = clients.id')

生成sql

Sql代码

SELECT clients.* FROM clients LEFT OUTER JOIN addresses ON addresses.client_id = clients.id   
SELECT clients.* FROM clients LEFT OUTER JOIN addresses ON addresses.client_id = clients.id

使用Array、Hash、Named Associations关联表
有如下model

Ruby代码

class Category < ActiveRecord::Base         has_many :posts end class Post < ActiveRecord::Base         belongs_to :category     has_many :comments     has_many :tags end class Comments <ActiveRecord::Base         belongs_to :post     has_one :guest end class Guest < ActiveRecord::Base         belongs_to :comment end 
class Category < ActiveRecord::Base 
	has_many :posts 
end 
class Post < ActiveRecord::Base 
	belongs_to :category  
	has_many :comments  	
	has_many :tags 
end 
class Comments <ActiveRecord::Base 
	belongs_to :post  
	has_one :guest 
end 
class Guest < ActiveRecord::Base 
	belongs_to :comment 
end

Ruby代码

#关联一个关系 Category.all :joins => :posts #关联多个关系 Post.all :joins => [:category, :comments]     #嵌套关联 Category.all :joins => {:posts => [{:comments => :guest}, :tags]}   
#关联一个关系
Category.all :joins => :posts
#关联多个关系
Post.all :joins => [:category, :comments] 
#嵌套关联
Category.all :joins => {:posts => [{:comments => :guest}, :tags]}

为关联查询结果设定条件

Ruby代码

time_range = (Time.now.midnight - 1.day)..Time.now.midnight Client.all :joins => :orders, :conditions => {'orders.created_at' => time_ran    #或者 time_range = (Time.now.midnight - 1.day)..Time.now.midnight Client.all :joins => :orders, :conditions => {:orders => {:created_at => time_range}}   
time_range = (Time.now.midnight - 1.day)..Time.now.midnight Client.all :joins => :orders, :conditions => {'orders.created_at' => time_ran
#或者
time_range = (Time.now.midnight - 1.day)..Time.now.midnight Client.all :joins => :orders, :conditions => {:orders => {:created_at => time_range}}

5、优化载入
以下代码，需要执行1 + 10次sql

Ruby代码

clients = Client.all(:limit => 10) clients.each do |client|         puts client.address.postcode     end 
clients = Client.all(:limit => 10) clients.each do |client| 
	puts client.address.postcode 
end

优化：

Ruby代码

clients = Client.all(:include => :address, :limit => 10)     clients.each do |client|         puts client.address.postcode     end 
clients = Client.all(:include => :address, :limit => 10) 
clients.each do |client| 
	puts client.address.postcode 
end

一次性载入post的所有分类和评论

Ruby代码

Post.all :include => [:category, :comments]   
Post.all :include => [:category, :comments]

载入category为1的所有post和cooment及tag

Ruby代码

Category.find 1, :include => {:posts => [{:comments => :guest}, :tags]}   
Category.find 1, :include => {:posts => [{:comments => :guest}, :tags]}

6、动态查询

Ruby代码

Client.find_by_name("Ryan")    Client.find_all_by_name("Ryan")    #！方法，没有记录时抛出ActiveRecord::RecordNotFound异常 Client.find_by_name!("Ryan")    #查询多个字段 Client.find_by_name_and_locked("Ryan", true)    #查询不到时就创建并保存 Client.find_or_create_by_name(params[:name])    #查询不到时创建一个实例，但不保存 Client.find_or_initialize_by_name('Ryan')  
Client.find_by_name("Ryan")
Client.find_all_by_name("Ryan")

#！方法，没有记录时抛出ActiveRecord::RecordNotFound异常
Client.find_by_name!("Ryan")

#查询多个字段
Client.find_by_name_and_locked("Ryan", true)

#查询不到时就创建并保存
Client.find_or_create_by_name(params[:name])
#查询不到时创建一个实例，但不保存
Client.find_or_initialize_by_name('Ryan')

7、find_by_sql

Ruby代码

Client.find_by_sql("SELECT * FROM clients INNER JOIN orders ON clients.id = orders.client_id ORDER clients.created_at desc")   
Client.find_by_sql("SELECT * FROM clients INNER JOIN orders ON clients.id = orders.client_id ORDER clients.created_at desc")

8、select_all
和find_by_sql类似，但不会用model实例化返回记录，你会得到一个hash数组

Ruby代码

Client.connection.select_all("SELECT * FROM clients WHERE id = '1'")   
Client.connection.select_all("SELECT * FROM clients WHERE id = '1'")

9、判断记录是否存在

Ruby代码

#通过id来查询 Client.exists?(1)    Client.exists?(1, 2, 3)    #or Client.exists?([1,2,3])    #通过其他条件来查询 Client.exists?(:conditions => "first_name = 'Ryan'")    #没有参数时，则：表是空的 ? false : true Client.exists?  
#通过id来查询
Client.exists?(1)

Client.exists?(1, 2, 3)
#or
Client.exists?([1,2,3])

#通过其他条件来查询
Client.exists?(:conditions => "first_name = 'Ryan'")

#没有参数时，则：表是空的 ? false : true
Client.exists?

10、计算

Ruby代码

#求结果集条数 Client.count(:conditons => "first_name = 'Ryan'")    #求某个字段非空白的条数 Client.count(:age)    #平均值 Client.average("orders_count")    #求最小值 Client.minimum("age")    #求最大值 Client.maximum("age")    #求和 Client.sum("orders_count")  
#求结果集条数
Client.count(:conditons => "first_name = 'Ryan'")

#求某个字段非空白的条数
Client.count(:age)

#平均值
Client.average("orders_count")

#求最小值
Client.minimum("age")

#求最大值
Client.maximum("age")

#求和
Client.sum("orders_count")

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