software Software is a set of computer programs and associated documentation and data. This is in contrast to hardware, from which the system is built and which actually performs the work. At the lowest programming level, executable code consist ...

, a data access object (DAO) is a pattern that provides an abstract

interface Interface or interfacing may refer to: Academic journals * ''Interface'' (journal), by the Electrochemical Society * '' Interface, Journal of Applied Linguistics'', now merged with ''ITL International Journal of Applied Linguistics'' * '' Int ...

to some type of

database In computing, a database is an organized collection of data stored and accessed electronically. Small databases can be stored on a file system, while large databases are hosted on computer clusters or cloud storage. The design of databases ...

or other persistence mechanism. By mapping application calls to the persistence layer, the DAO provides data operations without exposing database details. This isolation supports the

single responsibility principle The single-responsibility principle (SRP) is a computer programming principle that states that "A module should be responsible to one, and only one, actor." The term actor refers to a group (consisting of one or more stakeholders or users) that ...

. It separates the data access the application needs, in terms of domain-specific objects and data types (the DAO's public interface), from how these needs can be satisfied with a specific

DBMS In computing, a database is an organized collection of data stored and accessed electronically. Small databases can be stored on a file system, while large databases are hosted on computer clusters or cloud storage. The design of databases ...

(the implementation of the DAO). Although this

design pattern A design pattern is the re-usable form of a solution to a design problem. The idea was introduced by the architect Christopher Alexander and has been adapted for various other disciplines, particularly software engineering. The "Gang of Four" boo ...

is applicable to most programming languages, most software with persistence needs, and most databases, it is traditionally associated with

Java EE Jakarta EE, formerly Java Platform, Enterprise Edition (Java EE) and Java 2 Platform, Enterprise Edition (J2EE), is a set of specifications, extending Java SE with specifications for enterprise features such as distributed computing and web ser ...

applications and with

relational databases A relational database is a (most commonly digital) database based on the relational model of data, as proposed by E. F. Codd in 1970. A system used to maintain relational databases is a relational database management system (RDBMS). Many relatio ...

(accessed via the

JDBC Java Database Connectivity (JDBC) is an application programming interface (API) for the programming language Java, which defines how a client may access a database. It is a Java-based data access technology used for Java database connectivity. I ...

API because of its origin in

Sun Microsystems Sun Microsystems, Inc. (Sun for short) was an American technology company that sold computers, computer components, software, and information technology services and created the Java programming language, the Solaris operating system, ZFS, t ...

' best practice guidelines "Core J2EE Patterns".

Advantages

The primary advantage of using data access objects is the rigorous separation between two parts of an application that have no need to know anything about each other, and which therefore can evolve frequently and independently. Changing business logic can rely on a constant DAO interface, while changes to persistence logic do not affect DAO clients. All details of storage are hidden from the rest of the application (see

information hiding In computer science, information hiding is the principle of segregation of the ''design decisions'' in a computer program that are most likely to change, thus protecting other parts of the program from extensive modification if the design decisio ...

Unit testing In computer programming, unit testing is a software testing method by which individual units of source code—sets of one or more computer program modules together with associated control data, usage procedures, and operating procedures&md ...

code is facilitated by substituting a

test double In computer programming and computer science, programmers employ a technique called automated unit testing to reduce the likelihood of bugs occurring in the software. Frequently, the final release software consists of a complex set of objects or ...

for the DAO in the test, thereby making the tests independent of the persistence layer. In the context of the

Java Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's mo ...

programming language, DAO can be implemented in various ways. This can range from a fairly simple interface that separates data access from the application logic, to frameworks and commercial products. Technologies like

Java Persistence API Jakarta Persistence (JPA; formerly Java Persistence API) is a Jakarta EE application programming interface specification that describes the management of relational data in enterprise Java applications. Persistence in this context covers three ...

and Enterprise JavaBeans come built into application servers and can be used in applications that use a Java EE application server. Commercial products such as

TopLink Oracle TopLink is a mapping and persistence framework for Java developers. TopLink is produced by Oracle and is a part of Oracle's OracleAS, WebLogic, and OC4J servers. It is an object-persistence and object-transformation framework. TopLink p ...

are available based on object-relational mapping (ORM). Popular open source ORM software includes

Doctrine Doctrine (from la, doctrina, meaning "teaching, instruction") is a codification of beliefs or a body of teachings or instructions, taught principles or positions, as the essence of teachings in a given branch of knowledge or in a belief syste ...

, Hibernate,

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 ( Plain Old Java Objects). The mappings are decoupled from the application logic b ...

and JPA implementations such as

Apache OpenJPA OpenJPA is an open source implementation of the Java Persistence API specification. It is an object-relational mapping (ORM) solution for the Java language, which simplifies storing objects in databases. It is open-source software distributed und ...

Disadvantages

Potential disadvantages of using DAO include

leaky abstraction In software development, a leaky abstraction is an abstraction that leaks details that it is supposed to abstract away. As coined by Joel Spolsky, the Law of Leaky Abstractions states: This statement highlights a particularly problematic cause o ...

, code duplication, and

abstraction inversion In computer programming, abstraction inversion is an anti-pattern arising when users of a construct need functions implemented within it but not exposed by its interface. The result is that the users re-implement the required functions in terms o ...

. In particular, the abstraction of the DAO as a regular Java object can obscure the high cost of each database access. Developers may inadvertently make multiple database queries to retrieve information that could be returned in a single operation. If an application requires multiple DAOs, the same create, read, update, and delete code may have to be written for each DAO.

Tools and frameworks

ODB ODB may refer to: People * Ol' Dirty Bastard (1968–2004), American rapper and founding member of the Wu-Tang Clan * ODB (wrestler) (born 1978), Stage name of American professional wrestler Jessica Kresa * Original David Baker (born 1972), a monik ...

compiler-based object-relational mapping (ORM) system for C++ * ORMLite: Lightweight object-relational mapping (ORM) framework in Java for JDBC and Android * Microsoft Entity Framework * DBIx::Class object-relational mapping (ORM) module for

Perl Perl is a family of two high-level, general-purpose, interpreted, dynamic programming languages. "Perl" refers to Perl 5, but from 2000 to 2019 it also referred to its redesigned "sister language", Perl 6, before the latter's name was offic ...

* TuxORM: Simple object-relational mapping (ORM) library in Java for JDBC

References

, url=https://www.oracle.com/java/technologies/data-access-object.html {{Design Patterns Patterns Architectural pattern (computer science) Software design patterns

Advantages

Disadvantages

Tools and frameworks

See also

References