What is the difference between the Data Mapper, Table Data Gateway (Gateway), Data Access Object (DAO) and Repository patterns?

Question

I\'m trying to brush up on my design pattern skills, and I\'m curious what are the differences between these patterns? All of them seem like they are the same thing - encap

Answer 1

Below is just my understanding.

TableGateWay/RowDataGateWay: In this context, Gateway is referring a specific implementation that has each "domain object" mapping to each "domain object gateway". For example, if we have Person, then we will have a PersonGateway to store the domain object Person to database. If we have Person, Employee, Customer, etc, we will have PersonGateway, EmployeeGateway, and CustomerGateway. Each gateway will have specific CRUD function for that object and it has nothing to do with other gateway. There is no reusable code/module here. The gateway can be further divided into RowDataGateway or TableGateway, depends if you pass an "id" or an "object". Gateway is usually compared with Active record. It ties your domain model to database schema.

Repository/DataMapper/DAO: They are the same thing. They all refer to the Persistence layer that transfer database entities to domain model. Unlike gateway, the Repository/DataMapper/DAO hide the implementation. You don't know if there is a PersonGateway behind Person. It may, or it may not, you don't care. All you know is it must have CRUD operations supported for each domain object. It decouple the data source and domain model.