refactoring: unit of work (#1940)

Co-authored-by: Subhrodip Mohanta <hello@subho.xyz>
2026-10-13 14:16:02 +00:00 · 2022-01-08 17:57:11 +05:30
1 parent 11f20593b2
commit 3cc9bc2dea
@@ -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 
-> constantly updating this information and it causes high load on the database server. To make the 
+> Arms dealer has a database containing weapon information. Merchants all over the town are 
+> 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 {
-  private final Integer id;
-  private final String name;
-  private final String address;
-
-  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;
-  }
+@Getter
+@RequiredArgsConstructor
+public class Weapon {
+    private final Integer id;
+    private final String name;
 }
 ```

-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 StudentDatabase studentDatabase;
+    private final Map<String, List<Weapon>> context;
+    private final WeaponDatabase weaponDatabase;

-  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) {
-    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();
+    @Override
+    public void registerNew(Weapon weapon) {
+        LOGGER.info("Registering {} for insert in context.", weapon.getName());
+        register(weapon, UnitActions.INSERT.getActionValue());
    }

-    if (context.containsKey(IUnitOfWork.MODIFY)) {
-      commitModify();
-    }
-    if (context.containsKey(IUnitOfWork.DELETE)) {
-      commitDelete();
-    }
-    LOGGER.info("Commit finished.");
-  }
+    @Override
+    public void registerModified(Weapon weapon) {
+        LOGGER.info("Registering {} for modify in context.", weapon.getName());
+        register(weapon, UnitActions.MODIFY.getActionValue());

-  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() {
-    var modifiedStudents = context.get(IUnitOfWork.MODIFY);
-    for (var student : modifiedStudents) {
-      LOGGER.info("Modifying {} to database.", student.getName());
-      studentDatabase.modify(student);
+    @Override
+    public void registerDeleted(Weapon weapon) {
+        LOGGER.info("Registering {} for delete in context.", weapon.getName());
+        register(weapon, UnitActions.DELETE.getActionValue());
    }
-  }

-  private void commitDelete() {
-    var deletedStudents = context.get(IUnitOfWork.DELETE);
-    for (var student : deletedStudents) {
-      LOGGER.info("Deleting {} to database.", student.getName());
-      studentDatabase.delete(student);
+    private void register(Weapon weapon, String operation) {
+        var weaponsToOperate = context.get(operation);
+        if (weaponsToOperate == null) {
+            weaponsToOperate = new ArrayList<>();
+        }
+        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);
-    studentRepository.registerModified(shyam);
-    studentRepository.registerDeleted(gopi);
-    studentRepository.commit();
+// create some weapons
+var enchantedHammer = new Weapon(1, "enchanted hammer");
+var brokenGreatSword = new Weapon(2, "broken great sword");
+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