Merge pull request #642 from piyushchaudhari04/unit-of-work-pattern

#352 - Unit of work pattern implementation

pom.xml

@@ -145,6 +145,8 @@
         <module>event-sourcing</module>
         <module>data-transfer-object</module>
         <module>throttling</module>
+
+        <module>unit-of-work</module>
         <module>partial-response</module>
         <module>eip-wire-tap</module>
         <module>eip-splitter</module>

unit-of-work/README.md

@@ -0,0 +1,31 @@
+---
+layout: pattern
+title: Unit Of Work
+folder: unit-of-work
+permalink: /patterns/unit-of-work/
+
+categories: Architectural
+tags:
+ - Java
+ - KISS
+ - YAGNI
+ - Difficulty-Beginner
+---
+
+## Intent
+When a business transaction is completed, all the these updates are sent as one 
+  big unit of work to be persisted in a database in one go so as to minimize database trips. 
+
+![alt text](etc/unit-of-work.urm.png "unit-of-work")
+
+## Applicability
+Use the Unit Of Work pattern when
+
+* To optimize the time taken for database transactions.
+* To send changes to database as a unit of work which ensures atomicity of the transaction.
+* To reduce number of database calls.
+
+## Credits
+
+* [Design Pattern - Unit Of Work Pattern](https://www.codeproject.com/Articles/581487/Unit-of-Work-Design-Pattern)
+* [Unit Of Work](https://martinfowler.com/eaaCatalog/unitOfWork.html)

unit-of-work/etc/unit-of-work.ucls

@@ -0,0 +1,68 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<class-diagram version="1.2.1" 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.unitofwork.StudentDatabase" project="unit-of-work" 
+    file="/unit-of-work/src/main/java/com/iluwatar/unitofwork/StudentDatabase.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="170" y="406"/>    
+    <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>  
+  <interface id="2" language="java" name="com.iluwatar.unitofwork.IUnitOfWork" project="unit-of-work" 
+    file="/unit-of-work/src/main/java/com/iluwatar/unitofwork/IUnitOfWork.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="356" y="433"/>    
+    <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.unitofwork.App" project="unit-of-work" 
+    file="/unit-of-work/src/main/java/com/iluwatar/unitofwork/App.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="88" y="85"/>    
+    <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.unitofwork.StudentRepository" project="unit-of-work" 
+    file="/unit-of-work/src/main/java/com/iluwatar/unitofwork/StudentRepository.java" binary="false" 
+    corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="377" y="166"/>    
+    <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="5" language="java" name="com.iluwatar.unitofwork.Student" project="unit-of-work" 
+    file="/unit-of-work/src/main/java/com/iluwatar/unitofwork/Student.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="696" y="130"/>    
+    <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>  
+  <realization id="6">    
+    <end type="SOURCE" refId="4"/>    
+    <end type="TARGET" refId="2"/>  
+  </realization>  
+  <association id="7">    
+    <end type="SOURCE" refId="4" navigable="false">      
+      <attribute id="8" name="studentDatabase"/>      
+      <multiplicity id="9" minimum="0" maximum="1"/>    
+    </end>    
+    <end type="TARGET" refId="1" navigable="true"/>    
+    <display labels="true" multiplicity="true"/>  
+  </association>  
+  <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>

unit-of-work/etc/unit-of-work.urm.puml

@@ -0,0 +1,48 @@
+@startuml
+package com.iluwatar.unitofwork {
+  class App {
+    + App()
+    + main(args : String[]) {static}
+  }
+  interface IUnitOfWork<T> {
+    + DELETE : String {static}
+    + INSERT : String {static}
+    + MODIFY : String {static}
+    + commit() {abstract}
+    + registerDeleted(T) {abstract}
+    + registerModified(T) {abstract}
+    + registerNew(T) {abstract}
+  }
+  class Student {
+    - address : String
+    - id : Integer
+    - name : String
+    + Student(id : Integer, name : String, address : String)
+    + getAddress() : String
+    + getId() : Integer
+    + getName() : String
+  }
+  class StudentDatabase {
+    + StudentDatabase()
+    + delete(student : Student)
+    + insert(student : Student)
+    + modify(student : Student)
+  }
+  class StudentRepository {
+    - LOGGER : Logger {static}
+    - context : Map<String, List<Student>>
+    - studentDatabase : StudentDatabase
+    + StudentRepository(context : Map<String, List<Student>>, studentDatabase : StudentDatabase)
+    + commit()
+    - commitDelete()
+    - commitInsert()
+    - commitModify()
+    - register(student : Student, operation : String)
+    + registerDeleted(student : Student)
+    + registerModified(student : Student)
+    + registerNew(student : Student)
+  }
+}
+StudentRepository -->  "-studentDatabase" StudentDatabase
+StudentRepository ..|> IUnitOfWork 
+@enduml

unit-of-work/pom.xml

@@ -0,0 +1,25 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <parent>
+        <artifactId>java-design-patterns</artifactId>
+        <groupId>com.iluwatar</groupId>
+        <version>1.18.0-SNAPSHOT</version>
+    </parent>
+    <modelVersion>4.0.0</modelVersion>
+
+    <artifactId>unit-of-work</artifactId>
+    <dependencies>
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.mockito</groupId>
+            <artifactId>mockito-core</artifactId>
+        </dependency>
+    </dependencies>
+
+
+</project>

unit-of-work/src/main/java/com/iluwatar/unitofwork/App.java

@@ -0,0 +1,52 @@
+/*
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2014-2017 Piyush Chaudhari
+ *
+ * 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.unitofwork;
+
+import java.util.HashMap;
+import java.util.List;
+
+/**
+ * {@link App} Application for managing student data.
+ */
+public class App {
+  /**
+   *
+   * @param args no argument sent
+   */
+  public static void main(String[] args) {
+    Student ram = new Student(1, "Ram", "Street 9, Cupertino");
+    Student shyam = new Student(2, "Shyam", "Z bridge, Pune");
+    Student gopi = new Student(3, "Gopi", "Street 10, Mumbai");
+
+    HashMap<String, List<Student>> context = new HashMap<>();
+    StudentDatabase studentDatabase = new StudentDatabase();
+    StudentRepository studentRepository = new StudentRepository(context, studentDatabase);
+
+    studentRepository.registerNew(ram);
+    studentRepository.registerModified(shyam);
+    studentRepository.registerDeleted(gopi);
+    studentRepository.commit();
+  }
+}

unit-of-work/src/main/java/com/iluwatar/unitofwork/IUnitOfWork.java

@@ -0,0 +1,55 @@
+/*
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2014-2017 Piyush Chaudhari
+ *
+ * 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.unitofwork;
+
+/**
+ * @param <T> Any generic entity
+ */
+public interface IUnitOfWork<T> {
+  String INSERT = "INSERT";
+  String DELETE = "DELETE";
+  String MODIFY = "MODIFY";
+
+  /**
+   * Any register new operation occurring on UnitOfWork is only going to be performed on commit.
+   */
+  void registerNew(T entity);
+
+  /**
+   * Any register modify operation occurring on UnitOfWork is only going to be performed on commit.
+   */
+  void registerModified(T entity);
+
+  /**
+   * Any register delete operation occurring on UnitOfWork is only going to be performed on commit.
+   */
+  void registerDeleted(T entity);
+
+  /***
+   * All UnitOfWork operations batched together executed in commit only.
+   */
+  void commit();
+
+}

unit-of-work/src/main/java/com/iluwatar/unitofwork/Student.java

@@ -0,0 +1,57 @@
+/*
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2014-2017 Piyush Chaudhari
+ *
+ * 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.unitofwork;
+
+/**
+ * {@link Student} is an entity.
+ */
+public class Student {
+  private final Integer id;
+  private final String name;
+  private final String address;
+
+  /**
+   * @param id      student unique id
+   * @param name    name of student
+   * @param address address of student
+   */
+  public Student(Integer id, String name, String address) {
+    this.id = id;
+    this.name = name;
+    this.address = address;
+  }
+
+  public String getName() {
+    return name;
+  }
+
+  public Integer getId() {
+    return id;
+  }
+
+  public String getAddress() {
+    return address;
+  }
+}

unit-of-work/src/main/java/com/iluwatar/unitofwork/StudentDatabase.java

@@ -0,0 +1,43 @@
+/*
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2014-2017 Piyush Chaudhari
+ *
+ * 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.unitofwork;
+
+/**
+ * Act as Database for student records.
+ */
+public class StudentDatabase {
+
+  public void insert(Student student) {
+    //Some insert logic to DB
+  }
+
+  public void modify(Student student) {
+    //Some modify logic to DB
+  }
+
+  public void delete(Student student) {
+    //Some delete logic to DB
+  }
+}

unit-of-work/src/main/java/com/iluwatar/unitofwork/StudentRepository.java

@@ -0,0 +1,126 @@
+/*
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2014-2017 Piyush Chaudhari
+ *
+ * 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.unitofwork;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+
+/**
+ * {@link StudentRepository} Student database repository.
+ * supports unit of work for student data.
+ */
+public class StudentRepository implements IUnitOfWork<Student> {
+  private static final Logger LOGGER = LoggerFactory.getLogger(StudentRepository.class);
+
+  private Map<String, List<Student>> context;
+  private StudentDatabase studentDatabase;
+
+  /**
+   * @param context         set of operations to be perform during commit.
+   * @param studentDatabase Database for student records.
+   */
+  public StudentRepository(Map<String, List<Student>> context, StudentDatabase studentDatabase) {
+    this.context = context;
+    this.studentDatabase = studentDatabase;
+  }
+
+  @Override
+  public void registerNew(Student student) {
+    LOGGER.info("Registering {} for insert in context.", student.getName());
+    register(student, IUnitOfWork.INSERT);
+  }
+
+  @Override
+  public void registerModified(Student student) {
+    LOGGER.info("Registering {} for modify in context.", student.getName());
+    register(student, IUnitOfWork.MODIFY);
+
+  }
+
+  @Override
+  public void registerDeleted(Student student) {
+    LOGGER.info("Registering {} for delete in context.", student.getName());
+    register(student, IUnitOfWork.DELETE);
+  }
+
+  private void register(Student student, String operation) {
+    List<Student> studentsToOperate = context.get(operation);
+    if (studentsToOperate == null) {
+      studentsToOperate = new ArrayList<>();
+    }
+    studentsToOperate.add(student);
+    context.put(operation, studentsToOperate);
+  }
+
+  /**
+   * All UnitOfWork operations are batched and executed together on commit only.
+   */
+  @Override
+  public void commit() {
+    if (context == null || context.size() == 0) {
+      return;
+    }
+    LOGGER.info("Commit started");
+    if (context.containsKey(IUnitOfWork.INSERT)) {
+      commitInsert();
+    }
+
+    if (context.containsKey(IUnitOfWork.MODIFY)) {
+      commitModify();
+    }
+    if (context.containsKey(IUnitOfWork.DELETE)) {
+      commitDelete();
+    }
+    LOGGER.info("Commit finished.");
+  }
+
+  private void commitInsert() {
+    List<Student> studentsToBeInserted = context.get(IUnitOfWork.INSERT);
+    for (Student student : studentsToBeInserted) {
+      LOGGER.info("Saving {} to database.", student.getName());
+      studentDatabase.insert(student);
+    }
+  }
+
+  private void commitModify() {
+    List<Student> modifiedStudents = context.get(IUnitOfWork.MODIFY);
+    for (Student student : modifiedStudents) {
+      LOGGER.info("Modifying {} to database.", student.getName());
+      studentDatabase.modify(student);
+    }
+  }
+
+  private void commitDelete() {
+    List<Student> deletedStudents = context.get(IUnitOfWork.DELETE);
+    for (Student student : deletedStudents) {
+      LOGGER.info("Deleting {} to database.", student.getName());
+      studentDatabase.delete(student);
+    }
+  }
+}

unit-of-work/src/test/java/com/iluwatar/unitofwork/AppTest.java

@@ -0,0 +1,40 @@
+/*
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2014-2017 Piyush Chaudhari
+ *
+ * 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.unitofwork;
+
+import org.junit.Test;
+
+import java.io.IOException;
+
+/**
+ * AppTest
+ */
+public class AppTest {
+  @Test
+  public void test() throws IOException {
+    String[] args = {};
+    App.main(args);
+  }
+}

unit-of-work/src/test/java/com/iluwatar/unitofwork/StudentRepositoryTest.java

@@ -0,0 +1,147 @@
+/*
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2014-2017 Piyush Chaudhari
+ *
+ * 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.unitofwork;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.Mock;
+import org.mockito.runners.MockitoJUnitRunner;
+
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+import static org.junit.Assert.assertEquals;
+import static org.mockito.Mockito.*;
+
+/**
+ * tests {@link StudentRepository}
+ */
+@RunWith(MockitoJUnitRunner.class)
+public class StudentRepositoryTest {
+  private final Student student1 = new Student(1, "Ram", "street 9, cupertino");
+  private final Student student2 = new Student(1, "Sham", "Z bridge, pune");
+
+  private Map<String, List<Student>> context;
+  @Mock
+  private StudentDatabase studentDatabase;
+  private StudentRepository studentRepository;
+
+  @Before
+  public void setUp() throws Exception {
+    context = new HashMap<>();
+    studentRepository = new StudentRepository(context, studentDatabase);
+  }
+
+  @Test
+  public void shouldSaveNewStudentWithoutWritingToDb() throws Exception {
+    studentRepository.registerNew(student1);
+    studentRepository.registerNew(student2);
+
+    assertEquals(2, context.get(IUnitOfWork.INSERT).size());
+    verifyNoMoreInteractions(studentDatabase);
+  }
+
+  @Test
+  public void shouldSaveDeletedStudentWithoutWritingToDb() throws Exception {
+    studentRepository.registerDeleted(student1);
+    studentRepository.registerDeleted(student2);
+
+    assertEquals(2, context.get(IUnitOfWork.DELETE).size());
+    verifyNoMoreInteractions(studentDatabase);
+  }
+
+  @Test
+  public void shouldSaveModifiedStudentWithoutWritingToDb() throws Exception {
+    studentRepository.registerModified(student1);
+    studentRepository.registerModified(student2);
+
+    assertEquals(2, context.get(IUnitOfWork.MODIFY).size());
+    verifyNoMoreInteractions(studentDatabase);
+  }
+
+  @Test
+  public void shouldSaveAllLocalChangesToDb() throws Exception {
+    context.put(IUnitOfWork.INSERT, Collections.singletonList(student1));
+    context.put(IUnitOfWork.MODIFY, Collections.singletonList(student1));
+    context.put(IUnitOfWork.DELETE, Collections.singletonList(student1));
+
+    studentRepository.commit();
+
+    verify(studentDatabase, times(1)).insert(student1);
+    verify(studentDatabase, times(1)).modify(student1);
+    verify(studentDatabase, times(1)).delete(student1);
+  }
+
+  @Test
+  public void shouldNotWriteToDbIfContextIsNull() throws Exception {
+    StudentRepository studentRepository = new StudentRepository(null, studentDatabase);
+
+    studentRepository.commit();
+
+    verifyNoMoreInteractions(studentDatabase);
+  }
+
+  @Test
+  public void shouldNotWriteToDbIfNothingToCommit() throws Exception {
+    StudentRepository studentRepository = new StudentRepository(new HashMap<>(), studentDatabase);
+
+    studentRepository.commit();
+
+    verifyZeroInteractions(studentDatabase);
+  }
+
+  @Test
+  public void shouldNotInsertToDbIfNoRegisteredStudentsToBeCommitted() throws Exception {
+    context.put(IUnitOfWork.MODIFY, Collections.singletonList(student1));
+    context.put(IUnitOfWork.DELETE, Collections.singletonList(student1));
+
+    studentRepository.commit();
+
+    verify(studentDatabase, never()).insert(student1);
+  }
+
+  @Test
+  public void shouldNotModifyToDbIfNotRegisteredStudentsToBeCommitted() throws Exception {
+    context.put(IUnitOfWork.INSERT, Collections.singletonList(student1));
+    context.put(IUnitOfWork.DELETE, Collections.singletonList(student1));
+
+    studentRepository.commit();
+
+    verify(studentDatabase, never()).modify(student1);
+  }
+
+  @Test
+  public void shouldNotDeleteFromDbIfNotRegisteredStudentsToBeCommitted() throws Exception {
+    context.put(IUnitOfWork.INSERT, Collections.singletonList(student1));
+    context.put(IUnitOfWork.MODIFY, Collections.singletonList(student1));
+
+    studentRepository.commit();
+
+    verify(studentDatabase, never()).delete(student1);
+  }
+}