本章节展开对model的介绍：包括查增删改操作。紧接着上面一节《[ruby on rails] 跟我学之HelloWorld》

创建模型

使用命令创建模型

创建表post,默认自带两栏位 title :string, content:text ,  在模型里面按照约定使用单数post而不是复数posts

cd blog
rails g model post title:string content:text

输出：

      invoke  active_record
      create    db/migrate/20141203105453_create_posts.rb
      create    app/models/post.rb
      invoke    test_unit
      create      test/models/post_test.rb
      create      test/fixtures/posts.yml

db/migrate/20141203105453_create_posts.rb文件内容如下：

class CreatePosts < ActiveRecord::Migration
  def change
    create_table :posts do |t|
      t.string :title
      t.text :context

      t.timestamps
    end
  end
end

以上只是生成了迁移文件，而没有正式生成数据库。 需要运行以下指令来生成数据库。

rake db:migrate

相当于django的syncdb。 输出如下：

== 20141203105453 CreatePosts: migrating ======================================
-- create_table(:posts)
   -> 0.0021s
== 20141203105453 CreatePosts: migrated (0.0029s) =============================

从控制台访问模型

进入控制台，类似于django的manage shell指令，ror使用以下指令：

rails console

简写为 rails c

新增记录：

模型类.new -> 模型实例变量.save

2.1.5 :001 > p = Post.new(:title => "My First Post", :context=>"this is my first post")
 => #<Post id: nil, title: "My First Post", context: "this is my first post", created_at: nil, updated_at: nil>
2.1.5 :002 > p.save()
   (0.5ms)  begin transaction
  SQL (0.7ms)  INSERT INTO "posts" ("context", "created_at", "title", "updated_at") VALUES (?, ?, ?, ?)  [["context", "this is my first post"], ["created_at", "2014-12-03 11:44:50.954572"], ["title", "My First Post"], ["updated_at", "2014-12-03 11:44:50.954572"]]
   (23.0ms)  commit transaction
 => true

模型类.create

2.1.5 :003 > Post.create(:title => "create test", :context=>"test of create")
   (0.2ms)  begin transaction
  SQL (0.4ms)  INSERT INTO "posts" ("context", "created_at", "title", "updated_at") VALUES (?, ?, ?, ?)  [["context", "test of create"], ["created_at", "2014-12-03 11:48:08.779270"], ["title", "create test"], ["updated_at", "2014-12-03 11:48:08.779270"]]
   (21.9ms)  commit transaction
 => #<Post id: 2, title: "create test", context: "test of create", created_at: "2014-12-03 11:48:08", updated_at: "2014-12-03 11:48:08">

查询记录

模型类.all

2.1.5 :004 > posts = Post.all
  Post Load (0.6ms)  SELECT "posts".* FROM "posts"
 => #<ActiveRecord::Relation [#<Post id: 1, title: "My First Post", context: "this is my first post", created_at: "2014-12-03 11:44:50", updated_at: "2014-12-03 11:44:50">, #<Post id: 2, title: "create test", context: "test of create", created_at: "2014-12-03 11:48:08", updated_at: "2014-12-03 11:48:08">]>

模型类.find(id)

2.1.5 :005 > post = Post.find(2)
  Post Load (0.6ms)  SELECT  "posts".* FROM "posts"  WHERE "posts"."id" = ? LIMIT 1  [["id", 2]]
 => #<Post id: 2, title: "create test", context: "test of create", created_at: "2014-12-03 11:48:08", updated_at: "2014-12-03 11:48:08">

可以用[实例变量].[成员变量]的方式访问数据，如下：

2.1.5 :006 > post.title
 => "create test"
2.1.5 :007 > post.context
 => "test of create"

更新记录

模型实例变量.update -> 模型实例变量.save()

2.1.5 :008 > post.title = "test update"
 => "test update"
2.1.5 :009 > post.save()
   (0.4ms)  begin transaction
  SQL (1.2ms)  UPDATE "posts" SET "title" = ?, "updated_at" = ? WHERE "posts"."id" = 2  [["title", "test update"], ["updated_at", "2014-12-03 11:57:08.964494"]]
   (10.0ms)  commit transaction
 => true

模型实例变量.update_attribute(field,value)

2.1.5 :010 > post.update_attribute(:context,"test operation of update_attribute")
   (0.4ms)  begin transaction
  SQL (1.4ms)  UPDATE "posts" SET "context" = ?, "updated_at" = ? WHERE "posts"."id" = 2  [["context", "test operation of update_attribute"], ["updated_at", "2014-12-03 12:01:12.051869"]]
   (32.3ms)  commit transaction
 => true

模型实例变量.update_attributes(hash)

2.1.5 :013 > post.update_attributes(:title=>"test update_attribute 2", :context =>"content for test of update_attribute 2")
   (1.4ms)  begin transaction
  SQL (1.2ms)  UPDATE "posts" SET "context" = ?, "title" = ?, "updated_at" = ? WHERE "posts"."id" = 2  [["context", "content for test of update_attribute 2"], ["title", "test update_attribute 2"], ["updated_at", "2014-12-03 12:05:16.878764"]]
   (26.1ms)  commit transaction
 => true

删除记录

模型实例变量.destroy

2.1.5 :016 > post.destroy
   (0.3ms)  begin transaction
  SQL (1.3ms)  DELETE FROM "posts" WHERE "posts"."id" = ?  [["id", 2]]
   (23.6ms)  commit transaction
 => #<Post id: 2, title: "test update_attribute 2", context: "content for test of update_attribute 2", created_at: "2014-12-03 11:48:08", updated_at: "2014-12-03 12:05:16">

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