Data access object

A data access object (DAO) is an object that provides an abstract interface to some type of database or persistence mechanism, providing some specific operations without exposing details of the database. It provides a mapping from application calls to the persistence layer. This isolation separates the concerns of what data accesses the application needs, in terms of domain-specific objects and data types (the public interface of the DAO), and how these needs can be satisfied with a specific DBMS, database schema, etc. (the implementation of the DAO).

This design pattern is equally applicable to most programming languages, most types of software with persistence needs and most types of databases, but it is traditionally associated with Java EE applications and with relational databases accessed via the JDBC API because of its origin in Sun Microsystems' best practice guidelines^[1] ("Core J2EE Patterns") for that platform.

The advantage of using data access objects is the relatively simple and rigorous separation between two important parts of an application that can and should know almost nothing of each other, and which can be expected to evolve frequently and independently. Changing business logic can rely on the same DAO interface, while changes to persistence logic do not affect DAO clients as long as the interface remains correctly implemented.

§  Can be used in a large percentage of applications - anywhere data storage is required.

§  Hide all details of data storage from the rest of the application.

§  Act as an intermediary between the application and the database. They move data back and forth between objects and database records.

§  Allow ripple effects from possible changes to the persistence mechanism to be confined to a specific area

§  Appication is independent of the data access techniques and database dependency.

§  Offers loose coupling with the other layers of application

§  Allows to unit test the service layer using mock objects without connecting to database