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Merge pull request iluwatar#417 from inbravo/master
Data Mapper iluwatar#34
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‎.gitignore

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.idea
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*.iml
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*.swp
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datanucleus.log
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datanucleus.log
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/bin/
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/bin/
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/bin/
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data-mapper/src/main/resources/log4j.xml

‎data-mapper/etc/data-mapper.png

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‎data-mapper/etc/data-mapper.ucls

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<?xml version="1.0" encoding="UTF-8"?>
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<class-diagram version="1.1.9" icons="true" always-add-relationships="false" generalizations="true" realizations="true"
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associations="true" dependencies="false" nesting-relationships="true" router="FAN">
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<class id="1" language="java" name="com.iluwatar.datamapper.Student" project="java-design-patterns"
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file="/java-design-patterns/java/com/iluwatar/datamapper/Student.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="359" width="148" x="868" y="175"/>
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<display autosize="false" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</class>
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<interface id="2" language="java" name="com.iluwatar.datamapper.StudentDataMapper" project="java-design-patterns"
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file="/java-design-patterns/java/com/iluwatar/datamapper/StudentDataMapper.java" binary="false"
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corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="733" y="241"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</interface>
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<class id="3" language="java" name="com.iluwatar.datamapper.StudentDataMapperImpl" project="java-design-patterns"
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file="/java-design-patterns/java/com/iluwatar/datamapper/StudentDataMapperImpl.java" binary="false"
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corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="734" y="447"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</class>
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<class id="4" language="java" name="com.iluwatar.datamapper.App" project="java-design-patterns"
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file="/java-design-patterns/java/com/iluwatar/datamapper/App.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="501" y="341"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</class>
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<dependency id="5">
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<end type="SOURCE" refId="4"/>
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<end type="TARGET" refId="3"/>
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</dependency>
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<dependency id="6">
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<end type="SOURCE" refId="4"/>
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<end type="TARGET" refId="1"/>
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</dependency>
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<association id="7">
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<end type="SOURCE" refId="3" navigable="false">
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<attribute id="8" name="students"/>
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<multiplicity id="9" minimum="0" maximum="2147483647"/>
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</end>
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<end type="TARGET" refId="1" navigable="true"/>
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<display labels="true" multiplicity="true"/>
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</association>
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<dependency id="10">
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<end type="SOURCE" refId="4"/>
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<end type="TARGET" refId="2"/>
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</dependency>
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<realization id="11">
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<end type="SOURCE" refId="3"/>
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<end type="TARGET" refId="2"/>
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</realization>
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<classifier-display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</classifier-display>
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<association-display labels="true" multiplicity="true"/>
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</class-diagram>

‎data-mapper/index.md

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---
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layout: pattern
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title: Data Mapper
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folder: data-mapper
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permalink: /patterns/dm/
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categories: Persistence Tier
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tags:
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- Java
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- Difficulty-Beginner
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---
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## Intent
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A layer of mappers that moves data between objects and a database while keeping them independent of each other and the mapper itself
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![alt text](./etc/data-mapper.png "Data Mapper")
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## Applicability
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Use the Data Mapper in any of the following situations
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* when you want to decouple data objects from DB access layer
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* when you want to write multiple data retrieval/persistence implementations
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## Credits
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* [Data Mapper](http://richard.jp.leguen.ca/tutoring/soen343-f2010/tutorials/implementing-data-mapper/)

‎data-mapper/pom.xml

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<?xml version="1.0"?>
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<!--
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The MIT License
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Copyright (c) 2016 Amit Dixit
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Permission is hereby granted, free of charge, to any person obtaining a copy
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of this software and associated documentation files (the "Software"), to deal
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in the Software without restriction, including without limitation the rights
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to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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copies of the Software, and to permit persons to whom the Software is
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furnished to do so, subject to the following conditions:
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The above copyright notice and this permission notice shall be included in
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all copies or substantial portions of the Software.
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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THE SOFTWARE.
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-->
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<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
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<modelVersion>4.0.0</modelVersion>
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<parent>
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<groupId>com.iluwatar</groupId>
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<artifactId>java-design-patterns</artifactId>
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<version>1.12.0-SNAPSHOT</version>
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</parent>
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<artifactId>data-mapper</artifactId>
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<dependencies>
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<dependency>
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<groupId>junit</groupId>
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<artifactId>junit</artifactId>
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<scope>test</scope>
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</dependency>
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<dependency>
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<groupId>log4j</groupId>
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<artifactId>log4j</artifactId>
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</dependency>
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</dependencies>
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</project>

‎data-mapper/src/main/java/com/iluwatar/datamapper/App.java

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/**
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* The MIT License Copyright (c) 2016 Amit Dixit
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy of this software and
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* associated documentation files (the "Software"), to deal in the Software without restriction,
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* including without limitation the rights to use, copy, modify, merge, publish, distribute,
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* sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in all copies or
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* substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT
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* NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
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* DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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*/
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package com.iluwatar.datamapper;
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import java.util.Optional;
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import org.apache.log4j.Logger;
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/**
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* The Data Mapper (DM) is a layer of software that separates the in-memory objects from the
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* database. Its responsibility is to transfer data between the two and also to isolate them from
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* each other. With Data Mapper the in-memory objects needn't know even that there's a database
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* present; they need no SQL interface code, and certainly no knowledge of the database schema. (The
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* database schema is always ignorant of the objects that use it.) Since it's a form of Mapper ,
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* Data Mapper itself is even unknown to the domain layer.
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* <p>
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* The below example demonstrates basic CRUD operations: Create, Read, Update, and Delete.
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*
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*/
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public final class App {
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private static Logger log = Logger.getLogger(App.class);
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/**
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* Program entry point.
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*
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* @param args command line args.
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*/
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public static void main(final String... args) {
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/* Create new data mapper for type 'first' */
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final StudentDataMapper mapper = new StudentDataMapperImpl();
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/* Create new student */
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Student student = new Student(1, "Adam", 'A');
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/* Add student in respectibe store */
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mapper.insert(student);
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log.debug("App.main(), student : " + student + ", is inserted");
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/* Find this student */
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final Optional<Student> studentToBeFound = mapper.find(student.getStudentId());
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log.debug("App.main(), student : " + studentToBeFound + ", is searched");
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/* Update existing student object */
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student = new Student(student.getStudentId(), "AdamUpdated", 'A');
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/* Update student in respectibe db */
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mapper.update(student);
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log.debug("App.main(), student : " + student + ", is updated");
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log.debug("App.main(), student : " + student + ", is going to be deleted");
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/* Delete student in db */
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mapper.delete(student);
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}
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private App() {}
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}

‎data-mapper/src/main/java/com/iluwatar/datamapper/DataMapperException.java

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/**
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* The MIT License Copyright (c) 2016 Amit Dixit
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy of this software and
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* associated documentation files (the "Software"), to deal in the Software without restriction,
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* including without limitation the rights to use, copy, modify, merge, publish, distribute,
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* sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in all copies or
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* substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT
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* NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
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* DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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*/
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package com.iluwatar.datamapper;
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/**
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* Using Runtime Exception for avoiding dependancy on implementation exceptions. This helps in
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* decoupling.
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*
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* @author amit.dixit
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*
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*/
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public final class DataMapperException extends RuntimeException {
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private static final long serialVersionUID = 1L;
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/**
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* Constructs a new runtime exception with the specified detail message. The cause is not
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* initialized, and may subsequently be initialized by a call to {@link #initCause}.
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*
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* @param message the detail message. The detail message is saved for later retrieval by the
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* {@link #getMessage()} method.
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*/
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public DataMapperException(final String message) {
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super(message);
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}
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}

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