mirror of
https://github.com/tiennm99/java-design-patterns.git
synced 2026-05-15 08:59:01 +00:00
KyleSong30
55 lines
1.9 KiB
Markdown
55 lines
1.9 KiB
Markdown
---
|
||
title: Data Mapper
|
||
category: Architectural
|
||
language: en
|
||
tags:
|
||
- Decoupling
|
||
---
|
||
|
||
## Intent
|
||
A layer of mappers that moves data between objects and a database while keeping them independent of each other and the mapper itself
|
||
|
||
This layer consists of one or more mappers (or data access objects) that perform data transfer. The scope of mapper implementations varies.
|
||
A generic mapper will handle many different domain entity types, a dedicated mapper will handle one or a few.
|
||
|
||
## Explanation
|
||
|
||
Real-world example
|
||
|
||
> When accessing web resources through a browser, there is generally no need to interact with the server directly;
|
||
> the browser and the proxy server will complete the data acquisition operation, and the three will remain independent.
|
||
|
||
In plain words
|
||
|
||
> The data mapper will help complete the bi-directional transfer of persistence layer and in-memory data.
|
||
|
||
Wikipedia says
|
||
|
||
> A Data Mapper is a Data Access Layer that performs bidirectional transfer of data between a
|
||
> persistent data store (often a relational database) and an in-memory data representation (the domain layer).
|
||
|
||
Programmatic example
|
||
|
||
## Class diagram
|
||
|
||
|
||
## Applicability
|
||
Use the Data Mapper in any of the following situations
|
||
|
||
* when you want to decouple data objects from DB access layer
|
||
* when you want to write multiple data retrieval/persistence implementations
|
||
|
||
## Known uses
|
||
* [SqlSession.getMapper()](https://mybatis.org/mybatis-3/java-api.html)
|
||
|
||
## Consequences
|
||
|
||
> Neatly mapped persistence layer data
|
||
> Data model follows the single function principle
|
||
|
||
## Related patterns
|
||
* [Active Record Pattern](https://en.wikipedia.org/wiki/Active_record_pattern)
|
||
* [Object–relational Mapping](https://en.wikipedia.org/wiki/Object%E2%80%93relational_mapping)
|
||
|
||
## Credits
|
||
* [Data Mapper](http://richard.jp.leguen.ca/tutoring/soen343-f2010/tutorials/implementing-data-mapper/) |