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Data access object
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<h2 id="advantages">Advantages</h2> <p>Using data access objects (DAOs) offers a clear advantage: it separates two parts of an application that don't need to know about each other. This separation allows them to evolve independently. If business logic changes, it can rely on a consistent DAO interface. Meanwhile, modifications to persistence logic won't affect DAO clients.<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a><a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> </p><p>All details of storage are hidden from the rest of the application (see <a href="/facts/Information_hiding/dnSDPMaz">information hiding</a>). <a href="/facts/Unit_testing/SYoGGS3T">Unit testing</a> code is facilitated by substituting a <a href="/facts/Test_double/7vNKBfMk">test double</a> for the DAO in the test, thereby making the tests independent of the persistence layer. </p><p>In the context of the <a href="/facts/Java_(programming_language)/9ScgFyAL">Java</a> 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. </p><p>Technologies like <a href="/facts/Java_Persistence_API/mdw15jQI">Java Persistence API</a> and <a href="/facts/Enterprise_JavaBeans/3lpxQpDv">Enterprise JavaBeans</a> come built into application servers and can be used in applications that use a Java EE application server. Commercial products such as <a href="/facts/TopLink/ESDCyJsj">TopLink</a> are available based on <a href="/facts/Object%E2%80%93relational_mapping/sjIPEIfq">object–relational mapping</a> (ORM). Popular open source ORM software includes <a href="/facts/Doctrine_(PHP)/RGMGWXhn">Doctrine</a>, <a href="/facts/Hibernate_(Java)/7hHcgTkB">Hibernate</a>, <a href="/facts/IBATIS/H4mB2Yee">iBATIS</a> and JPA implementations such as <a href="/facts/Apache_OpenJPA/Qb8CKm6H">Apache OpenJPA</a>.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> </p> <h2 id="disadvantages">Disadvantages</h2> <p>Potential disadvantages of using DAO include <a href="/facts/Leaky_abstraction/muja0NP6">leaky abstraction</a>, <a href="/facts/Duplicate_code/adzaD7R2">code duplication</a>, and <a href="/facts/Abstraction_inversion/6Mr1aHqU">abstraction inversion</a>. 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.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> </p><p>Note that these disadvantages only appear when you have a separate DAO for each table and the SELECT query is prevented from accessing anything other than the target table. </p> <h2 id="tools-and-frameworks">Tools and frameworks</h2> <ul><li>ODB compiler-based <a href="/facts/Object%E2%80%93relational_mapping/sjIPEIfq">object–relational mapping</a> (ORM) system for C++</li> <li>ORMLite: Lightweight <a href="/facts/Object%E2%80%93relational_mapping/sjIPEIfq">object–relational mapping</a> (ORM) framework in Java for JDBC and Android<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a></li> <li><a href="/facts/Entity_Framework/20FoR2zr">Microsoft Entity Framework</a></li> <li>DBIx::Class <a href="/facts/Object%E2%80%93relational_mapping/sjIPEIfq">object–relational mapping</a> (ORM) module for <a href="/facts/Perl/fx31kjlT">Perl</a></li> <li>TuxORM: Simple <a href="/facts/Object%E2%80%93relational_mapping/sjIPEIfq">object–relational mapping</a> (ORM) library in Java for JDBC</li> <li><a href="/facts/Persist_(Java_tool)/JnnJE8hy">Persist (Java tool)</a> Java-based <a href="/facts/Object%E2%80%93relational_mapping/sjIPEIfq">object–relational mapping</a> and data access object tool</li></ul> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Create,_read,_update_and_delete/8KwxY2eH">Create, read, update and delete</a> (CRUD)</li> <li><a href="/facts/Data_access_layer/gFkhdxkU">Data access layer</a></li> <li><a href="/facts/Service_Data_Objects/CmYC3cL6">Service Data Objects</a></li> <li><a href="/facts/Object%E2%80%93relational_mapping/sjIPEIfq">Object–relational mapping</a></li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>"Core J2EE Patterns - Data Access Objects". Sun Microsystems Inc. 2007-08-02. <a href="http://www.oracle.com/technetwork/java/dataaccessobject-138824.html" target="_blank">http://www.oracle.com/technetwork/java/dataaccessobject-138824.html</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>"Data Access Object(DAO) Design Pattern". DigitalOcean. 2022-08-03. Retrieved 2024-07-08. <a href="https://www.digitalocean.com/community/tutorials/dao-design-pattern" target="_blank">https://www.digitalocean.com/community/tutorials/dao-design-pattern</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>"Data Access Object(DAO) Design Pattern". GeeksforGeeks. 2017-08-26. Retrieved 2024-07-08. <a href="https://www.geeksforgeeks.org/data-access-object-pattern/#8-advantages-of-the-data-access-object-designdao-pattern" target="_blank">https://www.geeksforgeeks.org/data-access-object-pattern/#8-advantages-of-the-data-access-object-designdao-pattern</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>"Data Access Object(DAO) Design Pattern". GeeksforGeeks. 2017-08-26. Retrieved 2024-01-29. <a href="https://www.geeksforgeeks.org/data-access-object-pattern/" target="_blank">https://www.geeksforgeeks.org/data-access-object-pattern/</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>See http://www.ibm.com/developerworks/java/library/j-genericdao/index.html for workarounds <a href="http://www.ibm.com/developerworks/java/library/j-genericdao/index.html" target="_blank">http://www.ibm.com/developerworks/java/library/j-genericdao/index.html</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>Hodgson, Kyle; Reid, Darren (2015-01-23). ServiceStack 4 Cookbook. Packt Publishing Ltd. p. Chapter 4. ISBN 9781783986576. Retrieved 22 June 2016. <a href="9781783986576" target="_blank">9781783986576</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> </ol>