In computer software

Computer software

Computer software, or just software, is a collection of computer programs and related data that provide the instructions for telling a computer what to do and how to do it....

, a data access object (DAO) is an object

Object (computer science)

In computer science, an object is any entity that can be manipulated by the commands of a programming language, such as a value, variable, function, or data structure...

 that provides an abstract interface

Interface (computer science)

In the field of computer science, an interface is a tool and concept that refers to a point of interaction between components, and is applicable at the level of both hardware and software...

 to some type of database

Database

A database is an organized collection of data for one or more purposes, usually in digital form. The data are typically organized to model relevant aspects of reality , in a way that supports processes requiring this information...

 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

Separation of concerns

In computer science, separation of concerns is the process of separating a computer program into distinct features that overlap in functionality as little as possible. A concern is any piece of interest or focus in a program. Typically, concerns are synonymous with features or behaviors...

 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 management system

A database management system is a software package with computer programs that control the creation, maintenance, and use of a database. It allows organizations to conveniently develop databases for various applications by database administrators and other specialists. A database is an integrated...

, database schema, etc. (the implementation of the DAO).

This design pattern

Design pattern

A design pattern in architecture and computer science is a formal way of documenting a solution to a design problem in a particular field of expertise. The idea was introduced by the architect Christopher Alexander in the field of architecture and has been adapted for various other disciplines,...

 is equally applicable to most programming languages, most types of software with persistence needs and most types of database, but it is traditionally associated with Java EE

Java Platform, Enterprise Edition

Java Platform, Enterprise Edition or Java EE is widely used platform for server programming in the Java programming language. The Java platform differs from the Java Standard Edition Platform in that it adds libraries which provide functionality to deploy fault-tolerant, distributed, multi-tier...

 applications and with relational databases accessed via the JDBC API because of its origin in Sun Microsystems' best practice guidelines ("Core J2EE Patterns") for that platform.

Advantages

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.

In the specific context of the Java

Java (programming language)

Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities...

 programming language, Data Access Objects as a design concept can be implemented in a number of ways. This can range from a fairly simple interface that separates the data access parts from the application logic, to frameworks and commercial products.
DAO coding paradigms can require some skill. Use of technologies like Java persistence technologies

Java Persistence API

The Java Persistence API, sometimes referred to as JPA, is a Java programming language framework managing relational data in applications using Java Platform, Standard Edition and Java Platform, Enterprise Edition....

 and JDO

Java Data Objects

Java Data Objects is a specification of Java object persistence. One of its features is a transparency of the persistent services to the domain model. JDO persistent objects are ordinary Java programming language classes ; there's no requirement for them to implement certain interfaces or extend...

 ensures to some extent that the design pattern is implemented. Technologies like Enterprise JavaBeans come built into application servers and can be used in applications that use a JEE application server. Commercial products like TopLink

TopLink

In computing, TopLink is an object-relational mapping package for Java developers. It provides a framework for storing Java objects in a relational database or for converting Java objects to XML documents....

 are available based on Object-relational mapping

Object-relational mapping

Object-relational mapping in computer software is a programming technique for converting data between incompatible type systems in object-oriented programming languages. This creates, in effect, a "virtual object database" that can be used from within the programming language...

 (ORM). Popular open source ORM products include Hibernate

Hibernate (Java)

Hibernate is an object-relational mapping library for the Java language, providing a framework for mapping an object-oriented domain model to a traditional relational database...

, Ebean

Ebean

Ebean is an object-relational mapping product written in Java. It is designed to be simpler to use and understand than JPA or JDO products.- Simple API :...

, pureQuery, iBATIS

IBATIS

iBATIS is a persistence framework which automates the mapping between SQL databases and objects in Java, .NET, and Ruby on Rails. In Java, the objects are POJOs . The mappings are decoupled from the application logic by packaging the SQL statements in XML configuration files...

 and Apache OpenJPA

Apache OpenJPA

OpenJPA is an open source implementation of the Java Persistence API specification. It is an object-relational mapping solution for the Java language, which simplifies storing objects in databases. It is open source software distributed under the Apache 2.0 Licence.- History :Kodo, a Java Data...

.

The expected benefit of use of Data Access Objects in a Java scenario is:

• Improved efficiency and performance of the data layer since it is standard reusable software.
• Modifications can be made to the DAO implementation without altering other decoupled modules of the application.

See also

• Create, read, update and delete (CRUD)
• Data Access Layer
  Data access layer
  A data access layer is a layer of a computer program which provides simplified access to data stored in persistent storage of some kind, such as an entity-relational database....
  
  
• Data Transfer Object
  Data Transfer Object
  Data transfer object , is a design pattern used to transfer data between software application subsystems. DTOs are often used in conjunction with data access objects to retrieve data from a database....
  
  
• Design Patterns (book)
• Object-relational mapping
  Object-relational mapping
  Object-relational mapping in computer software is a programming technique for converting data between incompatible type systems in object-oriented programming languages. This creates, in effect, a "virtual object database" that can be used from within the programming language...
  
  
• Service Data Objects
  Service Data Objects
  Service Data Objects is a technology that allows heterogeneous data to be accessed in a uniform way. The SDO specification was originally developed in 2004 as a joint collaboration between BEA and IBM and approved by the Java Community Process...
  
  

External links

• Core J2EE Patterns - Data Access Object
• Data Access Objects versus Object Relational Mapping
• Inner Class strategy

Tools and Frameworks

• AuDAO Generator for JDBC DAO (MySQL
  MySQL
  MySQL officially, but also commonly "My Sequel") is a relational database management system that runs as a server providing multi-user access to a number of databases. It is named after developer Michael Widenius' daughter, My...
  
  , Oracle
  Oracle Database
  The Oracle Database is an object-relational database management system produced and marketed by Oracle Corporation....
  
  ) and Google App Engine
  Google App Engine
  Google App Engine is a platform as a service cloud computing platform for developing and hosting web applications in Google-managed data centers. It virtualizes applications across multiple servers,...
  
   datastore
• CodeFutures (Firestorm/DAO) Generator for JDBC DAO, Spring DAO, Hibernate DAO
• ComtorDAO Data Access Object Library for java Data Access Object Library for java
• DB Solo EJB 3.0 DAO code generator
• EasyDriver Java libray to create queries in order to be used in a DAO context.
• IBM pureQuery data access platform
• JingDAO DAO framework
• MDAOG DAO code generator for PostgreSQL
  PostgreSQL
  PostgreSQL, often simply Postgres, is an object-relational database management system available for many platforms including Linux, FreeBSD, Solaris, MS Windows and Mac OS X. It is released under the PostgreSQL License, which is an MIT-style license, and is thus free and open source software...
  
   databases
• nHydrate DAO/DTO framework, code generator for .NET
• ODB
  ODB (C++)
  ODB is an object-relational mapping system for the C++ language. It allows an application developer to persist C++ objects to a relational database without having to deal with tables, columns, or SQL and without manually writing any mapping code...
  
   compiler-based object-relational mapping
  Object-relational mapping
  Object-relational mapping in computer software is a programming technique for converting data between incompatible type systems in object-oriented programming languages. This creates, in effect, a "virtual object database" that can be used from within the programming language...
  
   (ORM) system for C++
• ORMLite
  ORMLite
  ORMLite is an open source software framework that provides lightweight object relational mapping between Java classes and SQL databases. It supports JDBC databases as well as Android mobile platform...
  
  Lightweight Object Relational Mapping (ORM) Framework in Java for JDBC and Android
• PerfectJPattern Open Source Project, Provides componentized implementation of the DAO Pattern in Java (JPA, Hibernate and Spring)
• Persist ORM tool
• Simplest ORM
• EclipseLink Delivers a comprehensive open-source Java persistence solution addressing relational, XML, and database web services.