refactor unit of work

unit-of-work/README.md

@@ -12,20 +12,20 @@ tags:
 
 ## Intent
 
-When a business transaction is completed, all the the updates are sent as one big unit of work to be 
+When a business transaction is completed, all the updates are sent as one big unit of work to be 
 persisted in one go to minimize database round-trips. 
 
 ## Explanation
 
-Real world example
+Real-world example
 
-> We have a database containing student information. Administrators all over the country are 
+> Arms dealer has a database containing weapon information. Merchants all over the town are 
-> constantly updating this information and it causes high load on the database server. To make the 
+> constantly updating this information and it causes a high load on the database server. To make the 
 > load more manageable we apply to Unit of Work pattern to send many small updates in batches.       
 
 In plain words
 
-> Unit of Work merges many small database updates in single batch to optimize the number of 
+> Unit of Work merges many small database updates in a single batch to optimize the number of 
 > round-trips. 
 
 [MartinFowler.com](https://martinfowler.com/eaaCatalog/unitOfWork.html) says
@@ -35,37 +35,20 @@ In plain words
 
 **Programmatic Example**
 
-Here's the `Student` entity that is being persisted to the database.
+Here's the `Weapon` entity that is being persisted in the database.
 
 ```java
-public class Student {
+@Getter
-  private final Integer id;
+@RequiredArgsConstructor
-  private final String name;
+public class Weapon {
-  private final String address;
+    private final Integer id;
-
+    private final String name;
-  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;
-  }
 }
 ```
 
-The essence of the implementation is the `StudentRepository` implementing the Unit of Work pattern. 
+The essence of the implementation is the `ArmsDealer` implementing the Unit of Work pattern. 
 It maintains a map of database operations (`context`) that need to be done and when `commit` is 
-called it applies them in single batch.
+called it applies them in a single batch.
 
 ```java
 public interface IUnitOfWork<T> {
@@ -84,96 +67,117 @@ public interface IUnitOfWork<T> {
 }
 
 @Slf4j
-public class StudentRepository implements IUnitOfWork<Student> {
+@RequiredArgsConstructor
+public class ArmsDealer implements IUnitOfWork<Weapon> {
 
-  private final Map<String, List<Student>> context;
+    private final Map<String, List<Weapon>> context;
-  private final StudentDatabase studentDatabase;
+    private final WeaponDatabase weaponDatabase;
 
-  public StudentRepository(Map<String, List<Student>> context, StudentDatabase studentDatabase) {
+    @Override
-    this.context = context;
+    public void registerNew(Weapon weapon) {
-    this.studentDatabase = studentDatabase;
+        LOGGER.info("Registering {} for insert in context.", weapon.getName());
-  }
+        register(weapon, UnitActions.INSERT.getActionValue());
-
-  @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) {
-    var studentsToOperate = context.get(operation);
-    if (studentsToOperate == null) {
-      studentsToOperate = new ArrayList<>();
-    }
-    studentsToOperate.add(student);
-    context.put(operation, studentsToOperate);
-  }
-
-  @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)) {
+    @Override
-      commitModify();
+    public void registerModified(Weapon weapon) {
-    }
+        LOGGER.info("Registering {} for modify in context.", weapon.getName());
-    if (context.containsKey(IUnitOfWork.DELETE)) {
+        register(weapon, UnitActions.MODIFY.getActionValue());
-      commitDelete();
-    }
-    LOGGER.info("Commit finished.");
-  }
 
-  private void commitInsert() {
-    var studentsToBeInserted = context.get(IUnitOfWork.INSERT);
-    for (var student : studentsToBeInserted) {
-      LOGGER.info("Saving {} to database.", student.getName());
-      studentDatabase.insert(student);
     }
-  }
 
-  private void commitModify() {
+    @Override
-    var modifiedStudents = context.get(IUnitOfWork.MODIFY);
+    public void registerDeleted(Weapon weapon) {
-    for (var student : modifiedStudents) {
+        LOGGER.info("Registering {} for delete in context.", weapon.getName());
-      LOGGER.info("Modifying {} to database.", student.getName());
+        register(weapon, UnitActions.DELETE.getActionValue());
-      studentDatabase.modify(student);
     }
-  }
 
-  private void commitDelete() {
+    private void register(Weapon weapon, String operation) {
-    var deletedStudents = context.get(IUnitOfWork.DELETE);
+        var weaponsToOperate = context.get(operation);
-    for (var student : deletedStudents) {
+        if (weaponsToOperate == null) {
-      LOGGER.info("Deleting {} to database.", student.getName());
+            weaponsToOperate = new ArrayList<>();
-      studentDatabase.delete(student);
+        }
+        weaponsToOperate.add(weapon);
+        context.put(operation, weaponsToOperate);
+    }
+
+    /**
+     * 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(UnitActions.INSERT.getActionValue())) {
+            commitInsert();
+        }
+
+        if (context.containsKey(UnitActions.MODIFY.getActionValue())) {
+            commitModify();
+        }
+        if (context.containsKey(UnitActions.DELETE.getActionValue())) {
+            commitDelete();
+        }
+        LOGGER.info("Commit finished.");
+    }
+
+    private void commitInsert() {
+        var weaponsToBeInserted = context.get(UnitActions.INSERT.getActionValue());
+        for (var weapon : weaponsToBeInserted) {
+            LOGGER.info("Inserting a new weapon {} to sales rack.", weapon.getName());
+            weaponDatabase.insert(weapon);
+        }
+    }
+
+    private void commitModify() {
+        var modifiedWeapons = context.get(UnitActions.MODIFY.getActionValue());
+        for (var weapon : modifiedWeapons) {
+            LOGGER.info("Scheduling {} for modification work.", weapon.getName());
+            weaponDatabase.modify(weapon);
+        }
+    }
+
+    private void commitDelete() {
+        var deletedWeapons = context.get(UnitActions.DELETE.getActionValue());
+        for (var weapon : deletedWeapons) {
+            LOGGER.info("Scrapping {}.", weapon.getName());
+            weaponDatabase.delete(weapon);
+        }
     }
-  }
 }
 ```
 
-Finally, here's how we use the `StudentRepository` and `commit` the transaction.
+Here is how the whole app is put together.
 
 ```java
-    studentRepository.registerNew(ram);
+// create some weapons
-    studentRepository.registerModified(shyam);
+var enchantedHammer = new Weapon(1, "enchanted hammer");
-    studentRepository.registerDeleted(gopi);
+var brokenGreatSword = new Weapon(2, "broken great sword");
-    studentRepository.commit();
+var silverTrident = new Weapon(3, "silver trident");
+
+// create repository
+var weaponRepository = new ArmsDealer(new HashMap<String, List<Weapon>>(), new WeaponDatabase());
+
+// perform operations on the weapons
+weaponRepository.registerNew(enchantedHammer);
+weaponRepository.registerModified(silverTrident);
+weaponRepository.registerDeleted(brokenGreatSword);
+weaponRepository.commit();
+```
+
+Here is the console output.
+
+```
+21:39:21.984 [main] INFO com.iluwatar.unitofwork.ArmsDealer - Registering enchanted hammer for insert in context.
+21:39:21.989 [main] INFO com.iluwatar.unitofwork.ArmsDealer - Registering silver trident for modify in context.
+21:39:21.989 [main] INFO com.iluwatar.unitofwork.ArmsDealer - Registering broken great sword for delete in context.
+21:39:21.989 [main] INFO com.iluwatar.unitofwork.ArmsDealer - Commit started
+21:39:21.989 [main] INFO com.iluwatar.unitofwork.ArmsDealer - Inserting a new weapon enchanted hammer to sales rack.
+21:39:21.989 [main] INFO com.iluwatar.unitofwork.ArmsDealer - Scheduling silver trident for modification work.
+21:39:21.989 [main] INFO com.iluwatar.unitofwork.ArmsDealer - Scrapping broken great sword.
+21:39:21.989 [main] INFO com.iluwatar.unitofwork.ArmsDealer - Commit finished.
 ```
 
 ## Class diagram
@@ -186,7 +190,7 @@ 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.
+* To reduce the number of database calls.
 
 ## Tutorials
 

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

@@ -1,7 +1,7 @@
 <?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" 
+  <class id="1" language="java" name="com.iluwatar.unitofwork.WeaponDatabase" 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" 
@@ -28,7 +28,7 @@
       <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" 
+  <class id="4" language="java" name="com.iluwatar.unitofwork.ArmsDealer" 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"/>    
@@ -38,7 +38,7 @@
       <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" 
+  <class id="5" language="java" name="com.iluwatar.unitofwork.Weapon" 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" 

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

@@ -27,7 +27,7 @@ import java.util.HashMap;
 import java.util.List;
 
 /**
- * {@link App} Application for managing student data.
+ * {@link App} Application demonstrating unit of work pattern.
  */
 public class App {
   /**
@@ -37,17 +37,19 @@ public class App {
    */
 
   public static void main(String[] args) {
-    var ram = new Student(1, "Ram", "Street 9, Cupertino");
+    // create some weapons
-    var shyam = new Student(2, "Shyam", "Z bridge, Pune");
+    var enchantedHammer = new Weapon(1, "enchanted hammer");
-    var gopi = new Student(3, "Gopi", "Street 10, Mumbai");
+    var brokenGreatSword = new Weapon(2, "broken great sword");
+    var silverTrident = new Weapon(3, "silver trident");
 
-    var context = new HashMap<String, List<Student>>();
+    // create repository
-    var studentDatabase = new StudentDatabase();
+    var weaponRepository = new ArmsDealer(new HashMap<String, List<Weapon>>(),
-    var studentRepository = new StudentRepository(context, studentDatabase);
+            new WeaponDatabase());
 
-    studentRepository.registerNew(ram);
+    // perform operations on the weapons
-    studentRepository.registerModified(shyam);
+    weaponRepository.registerNew(enchantedHammer);
-    studentRepository.registerDeleted(gopi);
+    weaponRepository.registerModified(silverTrident);
-    studentRepository.commit();
+    weaponRepository.registerDeleted(brokenGreatSword);
+    weaponRepository.commit();
   }
 }

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

@@ -30,41 +30,41 @@ import lombok.RequiredArgsConstructor;
 import lombok.extern.slf4j.Slf4j;
 
 /**
- * {@link StudentRepository} Student database repository. supports unit of work for student data.
+ * {@link ArmsDealer} Weapon repository that supports unit of work for weapons.
  */
 @Slf4j
 @RequiredArgsConstructor
-public class StudentRepository implements IUnitOfWork<Student> {
+public class ArmsDealer implements IUnitOfWork<Weapon> {
 
-  private final Map<String, List<Student>> context;
+  private final Map<String, List<Weapon>> context;
-  private final StudentDatabase studentDatabase;
+  private final WeaponDatabase weaponDatabase;
 
   @Override
-  public void registerNew(Student student) {
+  public void registerNew(Weapon weapon) {
-    LOGGER.info("Registering {} for insert in context.", student.getName());
+    LOGGER.info("Registering {} for insert in context.", weapon.getName());
-    register(student, UnitActions.INSERT.getActionValue());
+    register(weapon, UnitActions.INSERT.getActionValue());
   }
 
   @Override
-  public void registerModified(Student student) {
+  public void registerModified(Weapon weapon) {
-    LOGGER.info("Registering {} for modify in context.", student.getName());
+    LOGGER.info("Registering {} for modify in context.", weapon.getName());
-    register(student, UnitActions.MODIFY.getActionValue());
+    register(weapon, UnitActions.MODIFY.getActionValue());
 
   }
 
   @Override
-  public void registerDeleted(Student student) {
+  public void registerDeleted(Weapon weapon) {
-    LOGGER.info("Registering {} for delete in context.", student.getName());
+    LOGGER.info("Registering {} for delete in context.", weapon.getName());
-    register(student, UnitActions.DELETE.getActionValue());
+    register(weapon, UnitActions.DELETE.getActionValue());
   }
 
-  private void register(Student student, String operation) {
+  private void register(Weapon weapon, String operation) {
-    var studentsToOperate = context.get(operation);
+    var weaponsToOperate = context.get(operation);
-    if (studentsToOperate == null) {
+    if (weaponsToOperate == null) {
-      studentsToOperate = new ArrayList<>();
+      weaponsToOperate = new ArrayList<>();
     }
-    studentsToOperate.add(student);
+    weaponsToOperate.add(weapon);
-    context.put(operation, studentsToOperate);
+    context.put(operation, weaponsToOperate);
   }
 
   /**
@@ -90,26 +90,26 @@ public class StudentRepository implements IUnitOfWork<Student> {
   }
 
   private void commitInsert() {
-    var studentsToBeInserted = context.get(UnitActions.INSERT.getActionValue());
+    var weaponsToBeInserted = context.get(UnitActions.INSERT.getActionValue());
-    for (var student : studentsToBeInserted) {
+    for (var weapon : weaponsToBeInserted) {
-      LOGGER.info("Saving {} to database.", student.getName());
+      LOGGER.info("Inserting a new weapon {} to sales rack.", weapon.getName());
-      studentDatabase.insert(student);
+      weaponDatabase.insert(weapon);
     }
   }
 
   private void commitModify() {
-    var modifiedStudents = context.get(UnitActions.MODIFY.getActionValue());
+    var modifiedWeapons = context.get(UnitActions.MODIFY.getActionValue());
-    for (var student : modifiedStudents) {
+    for (var weapon : modifiedWeapons) {
-      LOGGER.info("Modifying {} to database.", student.getName());
+      LOGGER.info("Scheduling {} for modification work.", weapon.getName());
-      studentDatabase.modify(student);
+      weaponDatabase.modify(weapon);
     }
   }
 
   private void commitDelete() {
-    var deletedStudents = context.get(UnitActions.DELETE.getActionValue());
+    var deletedWeapons = context.get(UnitActions.DELETE.getActionValue());
-    for (var student : deletedStudents) {
+    for (var weapon : deletedWeapons) {
-      LOGGER.info("Deleting {} to database.", student.getName());
+      LOGGER.info("Scrapping {}.", weapon.getName());
-      studentDatabase.delete(student);
+      weaponDatabase.delete(weapon);
     }
   }
 }

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

@@ -27,14 +27,12 @@ import lombok.Getter;
 import lombok.RequiredArgsConstructor;
 
 /**
- * {@link Student} is an entity.
+ * {@link Weapon} is an entity.
  */
 @Getter
 @RequiredArgsConstructor
-public class Student {
+public class Weapon {
 
   private final Integer id;
   private final String name;
-  private final String address;
-
 }

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

@@ -24,19 +24,19 @@
 package com.iluwatar.unitofwork;
 
 /**
- * Act as Database for student records.
+ * Act as database for weapon records.
  */
-public class StudentDatabase {
+public class WeaponDatabase {
 
-  public void insert(Student student) {
+  public void insert(Weapon weapon) {
     //Some insert logic to DB
   }
 
-  public void modify(Student student) {
+  public void modify(Weapon weapon) {
     //Some modify logic to DB
   }
 
-  public void delete(Student student) {
+  public void delete(Weapon weapon) {
     //Some delete logic to DB
   }
 }

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

@@ -36,102 +36,102 @@ import java.util.Map;
 import org.junit.jupiter.api.Test;
 
 /**
- * tests {@link StudentRepository}
+ * tests {@link ArmsDealer}
  */
 
-class StudentRepositoryTest {
+class ArmsDealerTest {
-  private final Student student1 = new Student(1, "Ram", "street 9, cupertino");
+  private final Weapon weapon1 = new Weapon(1, "battle ram");
-  private final Student student2 = new Student(1, "Sham", "Z bridge, pune");
+  private final Weapon weapon2 = new Weapon(1, "wooden lance");
 
-  private final Map<String, List<Student>> context = new HashMap<>();
+  private final Map<String, List<Weapon>> context = new HashMap<>();
-  private final StudentDatabase studentDatabase = mock(StudentDatabase.class);
+  private final WeaponDatabase weaponDatabase = mock(WeaponDatabase.class);
-  private final StudentRepository studentRepository = new StudentRepository(context, studentDatabase);;
+  private final ArmsDealer armsDealer = new ArmsDealer(context, weaponDatabase);;
 
   @Test
   void shouldSaveNewStudentWithoutWritingToDb() {
-    studentRepository.registerNew(student1);
+    armsDealer.registerNew(weapon1);
-    studentRepository.registerNew(student2);
+    armsDealer.registerNew(weapon2);
 
     assertEquals(2, context.get(UnitActions.INSERT.getActionValue()).size());
-    verifyNoMoreInteractions(studentDatabase);
+    verifyNoMoreInteractions(weaponDatabase);
   }
 
   @Test
   void shouldSaveDeletedStudentWithoutWritingToDb() {
-    studentRepository.registerDeleted(student1);
+    armsDealer.registerDeleted(weapon1);
-    studentRepository.registerDeleted(student2);
+    armsDealer.registerDeleted(weapon2);
 
     assertEquals(2, context.get(UnitActions.DELETE.getActionValue()).size());
-    verifyNoMoreInteractions(studentDatabase);
+    verifyNoMoreInteractions(weaponDatabase);
   }
 
   @Test
   void shouldSaveModifiedStudentWithoutWritingToDb() {
-    studentRepository.registerModified(student1);
+    armsDealer.registerModified(weapon1);
-    studentRepository.registerModified(student2);
+    armsDealer.registerModified(weapon2);
 
     assertEquals(2, context.get(UnitActions.MODIFY.getActionValue()).size());
-    verifyNoMoreInteractions(studentDatabase);
+    verifyNoMoreInteractions(weaponDatabase);
   }
 
   @Test
   void shouldSaveAllLocalChangesToDb() {
-    context.put(UnitActions.INSERT.getActionValue(), List.of(student1));
+    context.put(UnitActions.INSERT.getActionValue(), List.of(weapon1));
-    context.put(UnitActions.MODIFY.getActionValue(), List.of(student1));
+    context.put(UnitActions.MODIFY.getActionValue(), List.of(weapon1));
-    context.put(UnitActions.DELETE.getActionValue(), List.of(student1));
+    context.put(UnitActions.DELETE.getActionValue(), List.of(weapon1));
 
-    studentRepository.commit();
+    armsDealer.commit();
 
-    verify(studentDatabase, times(1)).insert(student1);
+    verify(weaponDatabase, times(1)).insert(weapon1);
-    verify(studentDatabase, times(1)).modify(student1);
+    verify(weaponDatabase, times(1)).modify(weapon1);
-    verify(studentDatabase, times(1)).delete(student1);
+    verify(weaponDatabase, times(1)).delete(weapon1);
   }
 
   @Test
   void shouldNotWriteToDbIfContextIsNull() {
-    var studentRepository = new StudentRepository(null, studentDatabase);
+    var weaponRepository = new ArmsDealer(null, weaponDatabase);
 
-    studentRepository.commit();
+    weaponRepository.commit();
 
-    verifyNoMoreInteractions(studentDatabase);
+    verifyNoMoreInteractions(weaponDatabase);
   }
 
   @Test
   void shouldNotWriteToDbIfNothingToCommit() {
-    var studentRepository = new StudentRepository(new HashMap<>(), studentDatabase);
+    var weaponRepository = new ArmsDealer(new HashMap<>(), weaponDatabase);
 
-    studentRepository.commit();
+    weaponRepository.commit();
 
-    verifyNoMoreInteractions(studentDatabase);
+    verifyNoMoreInteractions(weaponDatabase);
   }
 
   @Test
   void shouldNotInsertToDbIfNoRegisteredStudentsToBeCommitted() {
-    context.put(UnitActions.MODIFY.getActionValue(), List.of(student1));
+    context.put(UnitActions.MODIFY.getActionValue(), List.of(weapon1));
-    context.put(UnitActions.DELETE.getActionValue(), List.of(student1));
+    context.put(UnitActions.DELETE.getActionValue(), List.of(weapon1));
 
-    studentRepository.commit();
+    armsDealer.commit();
 
-    verify(studentDatabase, never()).insert(student1);
+    verify(weaponDatabase, never()).insert(weapon1);
   }
 
   @Test
   void shouldNotModifyToDbIfNotRegisteredStudentsToBeCommitted() {
-    context.put(UnitActions.INSERT.getActionValue(), List.of(student1));
+    context.put(UnitActions.INSERT.getActionValue(), List.of(weapon1));
-    context.put(UnitActions.DELETE.getActionValue(), List.of(student1));
+    context.put(UnitActions.DELETE.getActionValue(), List.of(weapon1));
 
-    studentRepository.commit();
+    armsDealer.commit();
 
-    verify(studentDatabase, never()).modify(student1);
+    verify(weaponDatabase, never()).modify(weapon1);
   }
 
   @Test
   void shouldNotDeleteFromDbIfNotRegisteredStudentsToBeCommitted() {
-    context.put(UnitActions.INSERT.getActionValue(), List.of(student1));
+    context.put(UnitActions.INSERT.getActionValue(), List.of(weapon1));
-    context.put(UnitActions.MODIFY.getActionValue(), List.of(student1));
+    context.put(UnitActions.MODIFY.getActionValue(), List.of(weapon1));
 
-    studentRepository.commit();
+    armsDealer.commit();
 
-    verify(studentDatabase, never()).delete(student1);
+    verify(weaponDatabase, never()).delete(weapon1);
   }
 }