Data access object: Difference between revisions

Revision as of 13:35, 14 March 2023

Revision as of 19:01, 14 March 2023

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Although this [[design pattern]] is applicable to most programming languages, most software with persistence needs, and most databases, it is traditionally associated with [[Java Platform, Enterprise Edition|Java EE]] applications and with [[relational databases]] (accessed via the [[JDBC]] API because of its origin in [[Sun Microsystems]]' best practice guidelines<ref>

{{cite web

| title = Core J2EE Patterns - Data Access Objects

| publisher = Sun Microsystems Inc.

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All details of storage are hidden from the rest of the application (see [[information hiding]]). [[Unit testing]] code is facilitated by substituting a [[test double]] for the DAO in the test, thereby making the tests independent of the persistence layer.

In the context of the [[Java (programming language)|Java]] 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]] 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]] are available based on [[object-relational mapping]] (ORM). Popular open source ORM software includes [[Doctrine (PHP)|Doctrine]], [[Hibernate (Java)|Hibernate]], [[iBATIS]] and JPA implementations such as [[Apache OpenJPA]].

== Disadvantages ==

Potential disadvantages of using DAO include [[leaky abstraction]],{{Citation needed |reason=What kind of leak?|date=August 2014}} [[Duplicate code|code duplication]], and [[abstraction inversion]]. 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.<ref>See http://www.ibm.com/developerworks/java/library/j-genericdao/index.html for workarounds</ref>

== Tools and frameworks ==