Ruby on Rails | Data Base

Database

• IDs columns are mostly generated by rails.
• To create a single migration use this command: rails generate migration create_tableName >> e.g. rails generate migration create_articles
after generating migration, you'll need to add column to your table. By adding it to your migration file. When you're finished type in: rake db:migrate
• To create table and everything related to it, you can simply type in this command line: rails generate scaffold Tablename firstColumn:dataTyp secondColumn:dataTyp >> e.g. rails generate scafold User username:string email:string
A scaffold in Rails is a full set of model, database migration for that model, controller to manipulate it, views to view and manipulate the data, and a test suite for each of the above.
• To migrate your database type in: rake db: migrate
Migrations are a convenient way to alter your database schema over time in a consistent and easy way. They use a Ruby DSL so that you don't have to write SQL by hand, allowing your schema and changes to be database independent.
• In 'rails console' you can change the data of your database using ruby code. For example, in the 'users' table you can grab any user by 'user_id' using User.find(userID) or if you want to toggle any Boolean information in your database, you can use this code: user = User.find(1) and user.toggle!(:admin) this code will change admin status of user 1 to true or false. change User and :admin to your need

Validation

• Validations are added in model class. 
• Example of validations of presence and length: validates :username, presence: true, length:{minimum: 3, maximum: 25}
• Example of validations of uniqueness: validates :email, uniqueness:{case_sensitive:false}
• If you want that all emails are to be formatted to lowercase in your database, simply add before_save {self.email = email.downcase} to your User model.
• more example: http://guides.rubyonrails.org/active_record_validations.html

Association

• To create foreign key association when creating scaffold, type in: rails generate scaffold TableName firstColumn:dataType secondColumn:dataType tableTobeAssociated:references >> e.g. rails generate scaffold Comment description:text user:references 
• Now we know that association has been made between users and comments, we might want to explicit some details of association. for example we want to tell our database that a user can have many comments, we have to add this line to the User model: has_many :comments
• If you want to associate two tables manually, you will have to make some changes to the model of each table. In the User model, we have to add has_many :articles ; and in the Article model, we have to add belongs_to :user
This will store the userID in your table whenever a comment is made.

 

Useful command line

• To go to rails console for testing your database : rails console
• To exit the console: exit
• To see the existing routes: rake routes
• To destroy scaffold in case you made mistakes: rails destroy scaffold TableName
• You have to be in your app directory before using all this command.