Object Relational Mapping

• ORM or Object Relational Mapping is technique often used map the data in databases to the world of objects in our programs
• Active Record is a Design Pattern which can be used to implement ORM
• Active Record is also the name of a very popular Ruby ORM Implementation

Implementation for SQL RDBMS Databases in Ruby

• Domain Specific Model classes are defined for specific tables
• Each Model class maps to a table
• Class methods map to actions on the table
  • find, -> SELECT
• An instance of the Model class maps to single row in the table
• An instance may refer to a 'yet-to-be-inserted' row
• The id ruby property maps to the PRIMARY KEY ID
• Instance methods map to actions on that single row
  • save -> INSERT or UPDATE
  • destroy -> DELETE

Discussion

• What about Related Objects?

Optional Code Along

• cd parksandrec
• bundle
• irb -r ./parksandrec.rb

Resources

• DataMapper Pattern
• Repository Pattern
• ORM Patterns: The Trade-Offs of Active Record and Data Mappers