Repository pattern in Ruby

What is a design pattern? What is Repository pattern, when and how should you use it? How does it work? I try to answer these questions in this presentation

Transcript

1. …a design pattern is a general reusable solution to a commonly occurring problem…
2. Repository Pattern Gergő Sulymosi // Digital Natives @trekdemo
3. Definition Mediates between the domain and data mapping layers using a collection-like interface for accessing domain objects. For humans and railsians:
 Moves #save, #find, #where and co. to a different place.
4. When should you use it? • Complex storage requirements • Using multiple backends/persistency solutions • Swap backends isn’t the intention! (but it makes you capable) • Complicated access rules • If testing your domain objects is too hard* * too hard to fake, stub or setup case the
5. When you shouldn’t • Small applications • Simple requirements for persistency
6. How does it work?
7. Business Logic Banana Repository Flat file Database Webservice FileAdapter DatabaseAdapter HttpAdapter #give_me(“banana-X”)
8. Business Logic Banana Repository Flat file Database Webservice FileAdapter DatabaseAdapter HttpAdapter Flat file Database Webservice
9. Business Logic Banana Repository Flat file Database Webservice FileAdapter DatabaseAdapter HttpAdapter Flat file Database Webservice
10. Business Logic Banana Repository Flat file Database Webservice FileAdapter DatabaseAdapter HttpAdapter Flat file Database Webservice Flat file Database Webservice
11. Implementation
12. class  Repo      def  self.adapter          @adapter      end      def  self.adapter=(adapter)          @adapter  =  adapter      end      def  self.find(klass,  id)          adapter.find(klass,  id)      end      def  self.all(klass)          adapter.all(klass)      end      def  self.create(object)          adapter.create(object)      end   …   end
13. class  InMemoryBackend      def  initialize          @counter  =  0          @map  =  {}      end      def  create(record)          @counter  =  @counter  +  1          record.id  ||=  @counter          map_for(record)[record.id]  =  record      end      def  find(klass,  id)          map_for_class(klass).fetch  id      end      def  all(klass)          map_for_class(klass).values      end      def  query(klass,  selector)          send  "query_#{selector.class.name.underscore}",  selector      end      private      def  map_for_class(klass)          @map[klass.to_s.to_sym]  ||=  {}      end      def  map_for(record)          map_for_class(record.class)      end   end
14. Usage Repo.find(Customer,  5)   Repo.all(Customer)   Repo.create(Cusomer.new(“Budapest.rb”)
15. Let's simplify it
16. module  RepoDelegation      def  save(record)          Repo.save(record)      end      def  all          Repo.all  object_class      end      def  find(id)          Repo.find  object_class,  id      end      def  delete(record)          Repo.delete  record      end      def  query(selector)          Repo.query  object_class,  selector      end      private      def  object_class          @object_class  ||=  self.to_s.match(/^(.+)Repo/)[1].constantize      end   end
17. class  CustomerRepo      extend  RepoDelegation   end   CustomerRepo.all          #  =>  [#<Customer  id:  “1”>,  …]   CustomerRepo.find(5)  #  =>  #<Customer  id:  “5”> Repo.find(Customer,  5)   Repo.all(Customer)   Repo.create(Cusomer.new(“Budapest.rb”) VS
18. Related patterns • Inversion of Control & Dependency Injection • DataMapper
19. • http://martinfowler.com/eaaCatalog/repository.html • http://hawkins.io/2013/10/implementing_the_repository_pattern/ • http://www.sitepoint.com/repository-design-pattern-demystified/ • https://msdn.microsoft.com/en-us/library/ff649690.aspx • http://blog.gauffin.org/2013/01/repository-pattern-done-right/ • http://en.wikipedia.org/wiki/Software_design_pattern
20. We’re hiring!