Adds active record super simple implementation

Author: kurenn

active_record/active_record.rb

@@ -0,0 +1,130 @@
+require "pg"
+require "singleton"
+require "pry"
+require "ostruct"
+require "active_support/inflector"
+
+class Connection
+  include Singleton
+
+  def connection
+    @connection ||= PG::Connection.open(dbname: "hsnews_development")
+  end
+end
+
+class ActiveRecord < OpenStruct
+
+  def self.connection
+    Connection.instance.connection
+  end
+
+  def self.table_name
+    self.name.downcase.pluralize
+  end
+
+  def self.all
+    result = self.connection.exec("SELECT * FROM #{self.table_name}")
+
+    result.map {|tuple| self.new(tuple) }
+  end
+
+  def self.find(id)
+    instance = nil
+    result = self.connection.exec("SELECT * FROM #{self.table_name}
+                                   WHERE id = #{id} limit 1")
+
+    result.each do |tuple|
+      instance = self.new(tuple)
+    end
+
+    raise "Not Record Found" if instance.nil?
+
+    instance
+  end
+
+  #INSERT INTO users(
+            #name, email, id)
+    #VALUES ('Abraham kuri', '[email protected]', 1);
+  def save
+    sql_column_names = self.to_h.keys.join(", ")
+    values = self.to_h.values.map {|value| "'#{value}'"}.join(', ')
+    #=> ['Abraham', 'kurenn...']
+    
+    self.class.connection.exec("INSERT INTO #{self.class.table_name} (
+                               #{sql_column_names})
+                               VALUES (#{values})")
+    self
+  end
+
+  def update(attr = {})
+
+    sql_update = attr.map {|k, v| "#{k} = '#{v}'" }.join(", ")
+
+    self.class.connection.exec("UPDATE #{self.class.table_name}
+                                SET #{sql_update}
+                                WHERE id = #{self.id}")
+    self.class.find(self.id)
+  end
+
+  def destroy
+    self.class.connection.exec("DELETE FROM #{self.class.table_name}
+                                WHERE id = #{self.id}")
+    nil
+  end
+
+  def self.create(attrs = {})
+    instance = self.new(attrs)
+    instance.save
+  end
+
+  def self.where(conditions = {})
+    sql_where = conditions.map {|k, v| "#{k} = '#{v}'" }.join(" AND ")
+
+    result = self.connection.exec("SELECT * FROM #{self.table_name}
+                          WHERE #{sql_where}")
+
+    result.map { |tuple| self.new(tuple) }
+  end
+
+  def self.has_many(*args)
+    association_class = args[0].to_s.classify #=> "Link"
+    association_method_name = args[0]
+    foreign_key = "#{self.name.downcase}_id"
+
+    define_method association_method_name do
+      association_class.constantize.where(foreign_key => self.id)
+    end
+  end
+
+  def self.belongs_to(*args)
+    association_model = args[0].to_s
+    association_method_name = args[0]
+
+    define_method association_method_name do |model=""|
+      instance_variable_set("@#{association_model}", association_model.classify.constantize.find(self.user_id)) if instance_variable_get("@#{association_model}").nil?
+      instance_variable_get("@#{association_model}")
+    end
+
+    define_method "#{association_method_name}=" do |model|
+      instance_variable_set("@#{association_model}", model)
+    end
+  end
+
+end
+
+class User < ActiveRecord
+  has_many :links
+end
+
+class Link < ActiveRecord
+  belongs_to :user
+end
+
+binding.pry
+
+User.all
+# => [#<User name: "">, #<User name: "">]
+
+puts "Hola"
+
+