Data access object

Last updated

In software, a data access object (DAO) is a pattern that provides an abstract interface to some type of database 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. 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 (the implementation of the DAO).

Contents

Although this design pattern is applicable to most programming languages, most software with persistence needs, and most databases, 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".

This object can be found in the Data Access layer of the 3-Tier Architecture.

There are various ways in which this object can be implemented:


Advantages

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.

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, 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, Hibernate, iBATIS and JPA implementations such as Apache OpenJPA. [2]

Disadvantages

Potential disadvantages of using DAO include leaky abstraction,[ citation needed ] 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. [3]

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.

Tools and frameworks

See also

Related Research Articles

<span class="mw-page-title-main">Jakarta EE</span> Set of specifications extending Java SE

Jakarta EE, formerly Java Platform, Enterprise Edition 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 services. Jakarta EE applications are run on reference runtimes, which can be microservices or application servers, which handle transactions, security, scalability, concurrency and management of the components they are deploying.

Object–relational mapping in computer science is a programming technique for converting data between a relational database and the heap of an object-oriented programming language. This creates, in effect, a virtual object database that can be used from within the programming language.

<span class="mw-page-title-main">Object–relational database</span> Database management system

An object–relational database (ORD), or object–relational database management system (ORDBMS), is a database management system (DBMS) similar to a relational database, but with an object-oriented database model: objects, classes and inheritance are directly supported in database schemas and in the query language. In addition, just as with pure relational systems, it supports extension of the data model with custom data types and methods.

Java Data Objects (JDO) is a specification of Java object persistence. One of its features is a transparency of the persistence services to the domain model. JDO persistent objects are ordinary Java programming language classes (POJOs); there is no requirement for them to implement certain interfaces or extend from special classes. JDO 1.0 was developed under the Java Community Process as JSR 12. JDO 2.0 was developed under JSR 243 and was released on May 10, 2006. JDO 2.1 was completed in Feb 2008, developed by the Apache JDO project. JDO 2.2 was released in October 2008. JDO 3.0 was released in April 2010.

Hibernate ORM is an object–relational mapping tool for the Java programming language. It provides a framework for mapping an object-oriented domain model to a relational database. Hibernate handles object–relational impedance mismatch problems by replacing direct, persistent database accesses with high-level object handling functions.

ADO.NET is a data access technology from the Microsoft .NET Framework that provides communication between relational and non-relational systems through a common set of components. ADO.NET is a set of computer software components that programmers can use to access data and data services from a database. It is a part of the base class library that is included with the Microsoft .NET Framework. It is commonly used by programmers to access and modify data stored in relational database systems, though it can also access data in non-relational data sources. ADO.NET is sometimes considered an evolution of ActiveX Data Objects (ADO) technology, but was changed so extensively that it can be considered an entirely new product.

Object–relational impedance mismatch is a set of difficulties going between data in relational data stores and data in domain-driven object models. Relational Database Management Systems (RDBMS) is the standard method for storing data in a dedicated database, while object-oriented (OO) programming is the default method for business-centric design in programming languages. The problem lies in neither relational databases nor OO programming, but in the conceptual difficulty mapping between the two logic models. Both logical models are differently implementable using database servers, programming languages, design patterns, or other technologies. Issues range from application to enterprise scale, whenever stored relational data is used in domain-driven object models, and vice versa. Object-oriented data stores can trade this problem for other implementation difficulties.

In software engineering, the active record pattern is an architectural pattern. It is found in software that stores in-memory object data in relational databases. It was named by Martin Fowler in his 2003 book Patterns of Enterprise Application Architecture. The interface of an object conforming to this pattern would include functions such as Insert, Update, and Delete, plus properties that correspond more or less directly to the columns in the underlying database table.

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. The result is a significant reduction in the amount of code that a developer needs to access a relational database using lower level APIs like JDBC and ODBC.

SAP NetWeaver Application Server or SAP Web Application Server is a component of SAP NetWeaver which works as a web application server for SAP products. All ABAP application servers including the message server represent the application layer of the multitier architecture of an ABAP-based SAP system. These application servers execute ABAP applications and communicate with the presentation components, the database, and also with each other, using the message server.

A data access layer (DAL) in computer software 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. This acronym is prevalently used in Microsoft environments.

The Spring Framework is an application framework and inversion of control container for the Java platform. The framework's core features can be used by any Java application, but there are extensions for building web applications on top of the Java EE platform. The framework does not impose any specific programming model.. The framework has become popular in the Java community as an addition to the Enterprise JavaBeans (EJB) model. The Spring Framework is free and open source software.

Jakarta Persistence is a Jakarta EE application programming interface specification that describes the management of relational data in enterprise Java applications.

The Doctrine Project is a set of PHP libraries primarily focused on providing persistence services and related functionality. Its most commonly known projects are the object–relational mapper (ORM) and the database abstraction layer it is built on top of.

Apache Empire-db is a Java library that provides a high level object-oriented API for accessing relational database management systems (RDBMS) through JDBC. Apache Empire-db is open source and provided under the Apache License 2.0 from the Apache Software Foundation.

Java Database Connectivity (JDBC) is an application programming interface (API) for the Java programming language which defines how a client may access a database. It is a Java-based data access technology used for Java database connectivity. It is part of the Java Standard Edition platform, from Oracle Corporation. It provides methods to query and update data in a database, and is oriented toward relational databases. A JDBC-to-ODBC bridge enables connections to any ODBC-accessible data source in the Java virtual machine (JVM) host environment.

Canigó is the name chosen for the Java EE framework of the Generalitat de Catalunya.

In software engineering, the data mapper pattern is an architectural pattern. It was named by Martin Fowler in his 2003 book Patterns of Enterprise Application Architecture. The interface of an object conforming to this pattern would include functions such as Create, Read, Update, and Delete, that operate on objects that represent domain entity types in a data store.

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 provides development tools and run-time functionalities that ease the development process and help increase functionality. Persistent object-oriented data is stored in relational databases which helps build high-performance applications. Storing data in either XML or relational databases is made possible by transforming it from object-oriented data.

References

  1. ↑ "Core J2EE Patterns - Data Access Objects". Sun Microsystems Inc. 2007-08-02.
  2. ↑ "Data Access Object(DAO) Design Pattern". GeeksforGeeks. 2017-08-26. Retrieved 2024-01-29.
  3. ↑ See http://www.ibm.com/developerworks/java/library/j-genericdao/index.html for workarounds
  4. ↑ Hodgson, Kyle; Reid, Darren (2015-01-23). ServiceStack 4 Cookbook. Packt Publishing Ltd. p. Chapter 4. ISBN   9781783986576 . Retrieved 22 June 2016.

|url=https://www.oracle.com/java/technologies/data-access-object.html

This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.