DB Mapper is an Object Relational Mapping framework which allows manipulating a database without explicitly writing SQL statements.

You can run following commands on your computer to run demo.

1. Clone the repository into your working directory.

$ git clone https://github.com/echeon/db-mapper.git

1. Go to db-mapper folder and run bundle install.

$ cd db-mapper
$ bundle install

1. Create SQLite3 tables by running the following command.

$ cat wizards.sql | sqlite3 wizards.db

1. Then, following tables will be generated and wizards.db file will be created.

• schools
• houses
• students

1. Open pry and require the demo file.

$ pry
[1] pry(main) > require_relative 'demo'

This example has three models: School, House, Student.

class School < SQLObject
  has_many :houses
end

class House < SQLObject
  belongs_to :school
  has_many :students
end

class Student < SQLObject
  belongs_to :house
  has_one_through :school, :house, :school
end

1. Play around! You can also run your own example by creating your own database and models. Just don't forget to add require_relative 'lib/sql_object' to your model file(s). Also, they all should inherit from SQLObject!

The followings are all methods available in DB Mapper. These examples show how you can use each method.

• ::new initializes an instance with provided hash

  [2] pry(main) > School.new(name: "Castelobruxo")
  => #<School:0x007fdda831bc98 @attributes={:name=>"Castelobruxo"}>
  

• ::columns takes no arguments and returns an array of column names

  [3] pry(main)> Student.columns
  => [:id, :name, :house_id]
  

• ::all takes no arguments and returns all objects in a class

  [4] pry(main) > House.all
  => [#<House:0x007fdda82e0a80 @attributes={:id=>1, :name=>"Gryffindor", :school_id=>1}>, ...]
  

• ::find(id) takes an integer as an argument and returns an object with matching id.

  [5] pry(main) > Student.find(1)
  => #<Student:0x007fdda8ab9d88 @attributes={:id=>1, :name=>"Harry Potter", :house_id=>1}>
  

• #insert inserts a new data to the database

  [6] pry(main) > school = School.new(name: "Castelobruxo")
  [7] pry(main) > school.insert
  [8] pry(main) > School.all
  => [...,
      #<School:0x007fdda818aac8 @attributes={:id=>4, :name=>"Castelobruxo"}>]
  

• #update saves updated attributes to the database

  [9] pry(main) > school = School.find(1)
  => #<School:0x007fdda89b0ae0 @attributes={:id=>1, :name=>"Hogwarts"}>
  [10] pry(main) > school.name = "Hogwarts School of Witchcraft and Wizardry"
  [11] pry(main) > school.update
  [12] pry(main) > School.find(1)
  => #<School:0x007fdda89b0ae0 @attributes={:id=>1, :name=>"Hogwarts School of Witchcraft and Wizardry"}>
  

• #save saves a new record using #insert if it doesn't exist in the database. OR, it saves with updated attributes to the database using #update if the record already exists in the database

• ::where takes an hash as an argument and returns an array of one or more objects that satisfy the all conditions

  [13] pry(main) > Student.where(name: "Hermione Granger")
  => [#<Student:0x007fb7e48cee90 @attributes={:id=>2, :name=>"Hermione Granger", :house_id=>1}>]
  

• ::belongs_to is equivalent to Rails Active Record's belongs_to association

  [14] pry(main) > harry = Student.find(1)
  [15] pry(main) > harry.house
  => #<House:0x007f90fe0f0578 @attributes={:id=>1, :name=>"Gryffindor", :school_id=>1}>
  

• ::has_many is equivalent to Rails Active Record's has_many association

  [16] pry(main) > gryffindor = House.find(1)
  [17] pry(main) > gryffindor.students
  => [#<Student:0x007f90fc80ee10 @attributes={:id=>1, :name=>"Harry Potter", :house_id=>1}>,
      #<Student:0x007f90fc80e0a0 @attributes={:id=>2, :name=>"Hermione Granger", :house_id=>1}>,
      #<Student:0x007f90fc80dd80 @attributes={:id=>3, :name=>"Ronald Weasley", :house_id=>1}>,
      #<Student:0x007f90fc80dbc8 @attributes={:id=>4, :name=>"Neville Longbottom", :house_id=>1}>,
      #<Student:0x007f90fc80d998 @attributes={:id=>5, :name=>"Dean Thomas", :house_id=>1}>]
  

• ::has_one_through is equivalent to Rails Active Record's has_many :through association

  [18] pry(main) > draco = Student.where(name: "Draco Malfoy").first
  [19] pry(main) > draco.school
  => #<School:0x007f90fc39db60 @attributes={:id=>1, :name=>"Hogwarts School of Witchcraft and Wizardry"}>