Merge pull request #417 from inbravo/master

Data Mapper #34

.gitignore

@@ -11,4 +11,9 @@ target
 .idea
 *.iml
 *.swp
-datanucleus.log
+datanucleus.log
+/bin/
+/bin/
+/bin/
+
+data-mapper/src/main/resources/log4j.xml

data-mapper/etc/data-mapper.ucls

@@ -0,0 +1,72 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<class-diagram version="1.1.9" icons="true" always-add-relationships="false" generalizations="true" realizations="true" 
+  associations="true" dependencies="false" nesting-relationships="true" router="FAN">  
+  <class id="1" language="java" name="com.iluwatar.datamapper.Student" project="java-design-patterns" 
+    file="/java-design-patterns/java/com/iluwatar/datamapper/Student.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="359" width="148" x="868" y="175"/>    
+    <display autosize="false" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </class>  
+  <interface id="2" language="java" name="com.iluwatar.datamapper.StudentDataMapper" project="java-design-patterns" 
+    file="/java-design-patterns/java/com/iluwatar/datamapper/StudentDataMapper.java" binary="false" 
+    corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="733" y="241"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </interface>  
+  <class id="3" language="java" name="com.iluwatar.datamapper.StudentDataMapperImpl" project="java-design-patterns" 
+    file="/java-design-patterns/java/com/iluwatar/datamapper/StudentDataMapperImpl.java" binary="false" 
+    corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="734" y="447"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </class>  
+  <class id="4" language="java" name="com.iluwatar.datamapper.App" project="java-design-patterns" 
+    file="/java-design-patterns/java/com/iluwatar/datamapper/App.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="501" y="341"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </class>  
+  <dependency id="5">    
+    <end type="SOURCE" refId="4"/>    
+    <end type="TARGET" refId="3"/>  
+  </dependency>  
+  <dependency id="6">    
+    <end type="SOURCE" refId="4"/>    
+    <end type="TARGET" refId="1"/>  
+  </dependency>  
+  <association id="7">    
+    <end type="SOURCE" refId="3" navigable="false">      
+      <attribute id="8" name="students"/>      
+      <multiplicity id="9" minimum="0" maximum="2147483647"/>    
+    </end>    
+    <end type="TARGET" refId="1" navigable="true"/>    
+    <display labels="true" multiplicity="true"/>  
+  </association>  
+  <dependency id="10">    
+    <end type="SOURCE" refId="4"/>    
+    <end type="TARGET" refId="2"/>  
+  </dependency>  
+  <realization id="11">    
+    <end type="SOURCE" refId="3"/>    
+    <end type="TARGET" refId="2"/>  
+  </realization>  
+  <classifier-display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+    sort-features="false" accessors="true" visibility="true">    
+    <attributes public="true" package="true" protected="true" private="true" static="true"/>    
+    <operations public="true" package="true" protected="true" private="true" static="true"/>  
+  </classifier-display>  
+  <association-display labels="true" multiplicity="true"/>
+</class-diagram>

data-mapper/index.md

@@ -0,0 +1,25 @@
+---
+layout: pattern
+title: Data Mapper
+folder: data-mapper
+permalink: /patterns/dm/
+categories: Persistence Tier
+tags:
+ - Java
+ - Difficulty-Beginner
+---
+
+## Intent
+A layer of mappers that moves data between objects and a database while keeping them independent of each other and the mapper itself
+
+![alt text](./etc/data-mapper.png "Data Mapper")
+
+## 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
+
+## Credits
+
+* [Data Mapper](http://richard.jp.leguen.ca/tutoring/soen343-f2010/tutorials/implementing-data-mapper/)

data-mapper/pom.xml

@@ -0,0 +1,45 @@
+<?xml version="1.0"?>
+<!--
+
+    The MIT License
+    Copyright (c) 2016 Amit Dixit
+
+    Permission is hereby granted, free of charge, to any person obtaining a copy
+    of this software and associated documentation files (the "Software"), to deal
+    in the Software without restriction, including without limitation the rights
+    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+    copies of the Software, and to permit persons to whom the Software is
+    furnished to do so, subject to the following conditions:
+
+    The above copyright notice and this permission notice shall be included in
+    all copies or substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+    THE SOFTWARE.
+
+-->
+<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">
+	<modelVersion>4.0.0</modelVersion>
+	<parent>
+		<groupId>com.iluwatar</groupId>
+		<artifactId>java-design-patterns</artifactId>
+		<version>1.12.0-SNAPSHOT</version>
+	</parent>
+	<artifactId>data-mapper</artifactId>
+	<dependencies>
+		<dependency>
+			<groupId>junit</groupId>
+			<artifactId>junit</artifactId>
+			<scope>test</scope>
+		</dependency>
+		<dependency>
+			<groupId>log4j</groupId>
+			<artifactId>log4j</artifactId>
+		</dependency>
+	</dependencies>
+</project>

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

@@ -0,0 +1,77 @@
+/**
+ * The MIT License Copyright (c) 2016 Amit Dixit
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of this software and
+ * associated documentation files (the "Software"), to deal in the Software without restriction,
+ * including without limitation the rights to use, copy, modify, merge, publish, distribute,
+ * sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all copies or
+ * substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT
+ * NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+ * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.iluwatar.datamapper;
+
+import java.util.Optional;
+
+import org.apache.log4j.Logger;
+
+/**
+ * The Data Mapper (DM) is a layer of software that separates the in-memory objects from the
+ * database. Its responsibility is to transfer data between the two and also to isolate them from
+ * each other. With Data Mapper the in-memory objects needn't know even that there's a database
+ * present; they need no SQL interface code, and certainly no knowledge of the database schema. (The
+ * database schema is always ignorant of the objects that use it.) Since it's a form of Mapper ,
+ * Data Mapper itself is even unknown to the domain layer.
+ * <p>
+ * The below example demonstrates basic CRUD operations: Create, Read, Update, and Delete.
+ * 
+ */
+public final class App {
+
+  private static Logger log = Logger.getLogger(App.class);
+
+  /**
+   * Program entry point.
+   * 
+   * @param args command line args.
+   */
+  public static void main(final String... args) {
+
+    /* Create new data mapper for type 'first' */
+    final StudentDataMapper mapper = new StudentDataMapperImpl();
+
+    /* Create new student */
+    Student student = new Student(1, "Adam", 'A');
+
+    /* Add student in respectibe store */
+    mapper.insert(student);
+
+    log.debug("App.main(), student : " + student + ", is inserted");
+
+    /* Find this student */
+    final Optional<Student> studentToBeFound = mapper.find(student.getStudentId());
+
+    log.debug("App.main(), student : " + studentToBeFound + ", is searched");
+
+    /* Update existing student object */
+    student = new Student(student.getStudentId(), "AdamUpdated", 'A');
+
+    /* Update student in respectibe db */
+    mapper.update(student);
+
+    log.debug("App.main(), student : " + student + ", is updated");
+    log.debug("App.main(), student : " + student + ", is going to be deleted");
+
+    /* Delete student in db */
+    mapper.delete(student);
+  }
+
+  private App() {}
+}

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

@@ -0,0 +1,42 @@
+/**
+ * The MIT License Copyright (c) 2016 Amit Dixit
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of this software and
+ * associated documentation files (the "Software"), to deal in the Software without restriction,
+ * including without limitation the rights to use, copy, modify, merge, publish, distribute,
+ * sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all copies or
+ * substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT
+ * NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+ * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.iluwatar.datamapper;
+
+/**
+ * Using Runtime Exception for avoiding dependancy on implementation exceptions. This helps in
+ * decoupling.
+ * 
+ * @author amit.dixit
+ *
+ */
+public final class DataMapperException extends RuntimeException {
+
+  private static final long serialVersionUID = 1L;
+
+  /**
+   * Constructs a new runtime exception with the specified detail message. The cause is not
+   * initialized, and may subsequently be initialized by a call to {@link #initCause}.
+   *
+   * @param message the detail message. The detail message is saved for later retrieval by the
+   *        {@link #getMessage()} method.
+   */
+  public DataMapperException(final String message) {
+    super(message);
+  }
+}