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">
转载请注明本文来自：http://www.cnblogs.com/Tommy-Yu/p/4141122.html，谢谢！