class.new 新建

class.find 查询

class.destroy 删除

变量查询

a="hahaha"

Product.find(:all,:conditions=>["title like ?","%#{a}%"])

Product.find(:all,:conditions=>["title like :title",:title=>"%#{a}%"])

Product.find(:all,:conditions=>["title like :title and price>:price",:title=>"%#{a}%",:prcie=>3])

相当

SELECT * FROM "products" WHERE (title like '%a%' and price>3)

字符串查询

Product.find(:all,:conditions=>{:title=>"a"})

相当

SELECT * FROM "products" WHERE ("products"."title" = 'a')

多条件查询合并

>> cs = [{:title=>"a",:price=>(1..20),:description=>"hhhhh"}, "title like '%b%'"]

=> [{:price=>1..20, :title=>"a", :description=>"hhhhh"}, "title like '%b%'"]

>> Product.all :conditions=> Product.merge_conditions(*cs)

相当

SELECT * FROM "products" WHERE (("products"."title" = 'a' AND "products"."price" BETWEEN 1 AND 20 AND "products"."description" = 'hhhhh') AND (title like '%b%'))

把条件设置数组

>> conditions = [] #定义一个数组

=> []

>> conditions << ["title like ?", 'a'] #把一个条件加到数组

=> [["title like ?", "a"]]

>> conditions << ["title like ?", 'a'] if params[:title].present? #加一个判断 非空时加入到数组

include附加查询（减少N+1次查询）

LineItem.all :conditions => "products.title => 'a'", :include => :product

jions附加查询

LineItem.all :conditions => "products.title like '%a%'", :joins => :product

想当

SELECT "line_items".* FROM "line_items" INNER JOIN "products" ON "products".id = "line_items".product_id WHERE (products.title like '%a%')

select查询

Product.find(:all,:select=>"title,price")

相当

SELECT title,price FROM "products"

readonly只读查询

>> p=Product.first

=> #.....

>> p=Product.first(:readonly=>true)

=> #....

>> p.title="xxxxxxxxx"

=> "xxxxxxxxx"

>> p.save #抛出异常

from 指定表名

group 指定分组

limit 指定条数

offset 指定起始数

find_by_sql 直接执行sql语句

获取字段统计信息

Product.average(:price)

Product.maximum(:price)

Product.minimum(:price)

Product.sum(:price)

Product.count()

动态查询

Product.find_by_title_and_price（"测试",78.9） #只查第一条first 结果：title和price

Product.find_all_by_title_and_price（"测试",78.9） #返回数组 结果：title和price

Product.find_or_create_by_title("hahahaha") #查询并保存

Product.find_or_initialize_by_title("aoiokkok") #查询，如果没有初始化

查看日志

tail -f log/development.log