[Ruby on Rails] and I learned the change and delete operation based on Rails console

This chapter launches the introduction of model: including check and delete operation. And then the above section, [Ruby on Rails] and I learned the HelloWorld

Creating models using commands to create models

Create a table post, default comes with two field title:string, Content:text, use the singular post instead of the plural in the model by convention posts

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

Output:

  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

The contents of the Db/migrate/20141203105453_create_posts.rb file are as follows:

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

      t.timestamps
    end
  end
end

The above is just a migration file generated, not a formal database build. You need to run the following command to build the database.

Rake Db:migrate

Equivalent to Django's syncdb. The output is as follows:

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

Accessing the model from the console

Entering the console, similar to the Django Manage Shell directive, ROR uses the following command:

Rails Console

Abbreviated to Rails C

New records:

Model class. New model instance variable. 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

Model class. 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">

Query records

Model class. 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">]>

Model class. 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">

You can use the [instance variable].[ Member variable] to access the data as follows:

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

Update record

Model instance variable. Update, model instance variable. 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

Model instance variable. 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

Model instance variable. 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

Deleting records

The model instance variable. 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">

Reprint please specify this article from: http://www.cnblogs.com/Tommy-Yu/p/4141122.html, thank you!

[Ruby on Rails] and I learned the change and delete operation based on Rails console