java-design-patterns/repository/README.md

---
layout: pattern
title: Repository
folder: repository
permalink: /patterns/repository/
pumlid: JSV13OCm30NGLM00udktCS42eyI9xE-YRjyUUtjlLQij3qblomNCU14vF-LKNBbdYDTX44EfevEsV1ZiTFERjqD2Jzic0-8Mr3b-89SvGZ7yGuBwrvBUoypUlW00
categories: Persistence Tier
tags:
 - Java
 - Difficulty-Intermediate
 - Spring
---

## Intent
Repository layer is added between the domain and data mapping
layers to isolate domain objects from details of the database access code and
to minimize scattering and duplication of query code. The Repository pattern is
especially useful in systems where number of domain classes is large or heavy
querying is utilized.

![alt text](./etc/repository.png "Repository")

## Applicability
Use the Repository pattern when

* the number of domain objects is large
* you want to avoid duplication of query code
* you want to keep the database querying code in single place
* you have multiple data sources

## Real world examples

* [Spring Data](http://projects.spring.io/spring-data/)

## Credits

* [Don’t use DAO, use Repository](http://thinkinginobjects.com/2012/08/26/dont-use-dao-use-repository/)
* [Advanced Spring Data JPA - Specifications and Querydsl](https://spring.io/blog/2011/04/26/advanced-spring-data-jpa-specifications-and-querydsl/)
-												Work towards #56: Splitting up the README

I did the job and splitted up the readme, hopefully everything was
splitted correctly...

											
										
										
											2015-08-13 23:54:40 +02:00
+								---
 								layout: pattern
 								title: Repository
 								folder: repository
-												Work towards #56: Add permalink to every pattern

This makes cleaner URLs thanks to jekyll

											
										
										
											2015-08-15 18:03:05 +02:00
+								permalink: /patterns/repository/
-												Work on #190: Commit initial pumlId's added by the script

											
										
										
											2016-08-30 15:10:34 +02:00
+								pumlid: JSV13OCm30NGLM00udktCS42eyI9xE-YRjyUUtjlLQij3qblomNCU14vF-LKNBbdYDTX44EfevEsV1ZiTFERjqD2Jzic0-8Mr3b-89SvGZ7yGuBwrvBUoypUlW00
-												Categorize and tag all patterns #213

											
										
										
											2015-12-28 15:52:44 +02:00
+								categories: Persistence Tier
 								tags:
 								 - Java
 								 - Difficulty-Intermediate
 								 - Spring
-												Work towards #56: Splitting up the README

I did the job and splitted up the readme, hopefully everything was
splitted correctly...

											
										
										
											2015-08-13 23:54:40 +02:00
+								---
-												Use headings instead of bold text in index.md #238

											
										
										
											2016-01-03 21:14:30 +01:00
+								## Intent
 								Repository layer is added between the domain and data mapping
-												Work towards #56: Splitting up the README

I did the job and splitted up the readme, hopefully everything was
splitted correctly...

											
										
										
											2015-08-13 23:54:40 +02:00
+								layers to isolate domain objects from details of the database access code and
 								to minimize scattering and duplication of query code. The Repository pattern is
 								especially useful in systems where number of domain classes is large or heavy
 								querying is utilized.
 								![alt text](./etc/repository.png "Repository")
-												Use headings instead of bold text in index.md #238

											
										
										
											2016-01-03 21:14:30 +01:00
+								## Applicability
 								Use the Repository pattern when
-												Work towards #56: Splitting up the README

I did the job and splitted up the readme, hopefully everything was
splitted correctly...

											
										
										
											2015-08-13 23:54:40 +02:00
 								* the number of domain objects is large
 								* you want to avoid duplication of query code
 								* you want to keep the database querying code in single place
 								* you have multiple data sources
-												Use headings instead of bold text in index.md #238

											
										
										
											2016-01-03 21:14:30 +01:00
+								## Real world examples
-												Work towards #56: Splitting up the README

I did the job and splitted up the readme, hopefully everything was
splitted correctly...

											
										
										
											2015-08-13 23:54:40 +02:00
-												Work towards #56: Add permalink to every pattern

This makes cleaner URLs thanks to jekyll

											
										
										
											2015-08-15 18:03:05 +02:00
+								* [Spring Data](http://projects.spring.io/spring-data/)
-												Fix #216 Repository vs DAO

											
										
										
											2015-11-27 11:22:33 +08:00
-												Use headings instead of bold text in index.md #238

											
										
										
											2016-01-03 21:14:30 +01:00
+								## Credits
-												Fix #216 Repository vs DAO

											
										
										
											2015-11-27 11:22:33 +08:00
 								* [Don’t use DAO, use Repository](http://thinkinginobjects.com/2012/08/26/dont-use-dao-use-repository/)
 								* [Advanced Spring Data JPA - Specifications and Querydsl](https://spring.io/blog/2011/04/26/advanced-spring-data-jpa-specifications-and-querydsl/)