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refactoring: unit of work (#1940)
Co-authored-by: Subhrodip Mohanta <[email protected]>
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‎unit-of-work/README.md

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@@ -12,20 +12,20 @@ tags:
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## Intent
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When a business transaction is completed, all the the updates are sent as one big unit of work to be
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When a business transaction is completed, all the updates are sent as one big unit of work to be
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persisted in one go to minimize database round-trips.
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## Explanation
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Real world example
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Real-world example
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> We have a database containing student information. Administrators all over the country are
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> constantly updating this information and it causes high load on the database server. To make the
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> Arms dealer has a database containing weapon information. Merchants all over the town are
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> constantly updating this information and it causes a high load on the database server. To make the
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> load more manageable we apply to Unit of Work pattern to send many small updates in batches.
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In plain words
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> Unit of Work merges many small database updates in single batch to optimize the number of
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> Unit of Work merges many small database updates in a single batch to optimize the number of
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> round-trips.
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[MartinFowler.com](https://martinfowler.com/eaaCatalog/unitOfWork.html) says
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**Programmatic Example**
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Here's the `Student` entity that is being persisted to the database.
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Here's the `Weapon` entity that is being persisted in the database.
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```java
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public class Student {
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private final Integer id;
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private final String name;
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private final String address;
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public Student(Integer id, String name, String address) {
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this.id = id;
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this.name = name;
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this.address = address;
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}
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public String getName() {
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return name;
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}
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public Integer getId() {
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return id;
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}
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public String getAddress() {
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return address;
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}
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@Getter
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@RequiredArgsConstructor
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public class Weapon {
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private final Integer id;
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private final String name;
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}
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```
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The essence of the implementation is the `StudentRepository` implementing the Unit of Work pattern.
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The essence of the implementation is the `ArmsDealer` implementing the Unit of Work pattern.
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It maintains a map of database operations (`context`) that need to be done and when `commit` is
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called it applies them in single batch.
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called it applies them in a single batch.
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```java
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public interface IUnitOfWork<T> {
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}
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@Slf4j
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public class StudentRepository implements IUnitOfWork<Student> {
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private final Map<String, List<Student>> context;
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private final StudentDatabase studentDatabase;
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public StudentRepository(Map<String, List<Student>> context, StudentDatabase studentDatabase) {
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this.context = context;
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this.studentDatabase = studentDatabase;
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}
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@Override
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public void registerNew(Student student) {
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LOGGER.info("Registering {} for insert in context.", student.getName());
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register(student, IUnitOfWork.INSERT);
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}
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@Override
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public void registerModified(Student student) {
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LOGGER.info("Registering {} for modify in context.", student.getName());
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register(student, IUnitOfWork.MODIFY);
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}
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@Override
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public void registerDeleted(Student student) {
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LOGGER.info("Registering {} for delete in context.", student.getName());
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register(student, IUnitOfWork.DELETE);
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}
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private void register(Student student, String operation) {
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var studentsToOperate = context.get(operation);
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if (studentsToOperate == null) {
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studentsToOperate = new ArrayList<>();
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@RequiredArgsConstructor
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public class ArmsDealer implements IUnitOfWork<Weapon> {
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private final Map<String, List<Weapon>> context;
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private final WeaponDatabase weaponDatabase;
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@Override
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public void registerNew(Weapon weapon) {
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LOGGER.info("Registering {} for insert in context.", weapon.getName());
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register(weapon, UnitActions.INSERT.getActionValue());
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}
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studentsToOperate.add(student);
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context.put(operation, studentsToOperate);
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}
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@Override
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public void commit() {
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if (context == null || context.size() == 0) {
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return;
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@Override
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public void registerModified(Weapon weapon) {
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LOGGER.info("Registering {} for modify in context.", weapon.getName());
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register(weapon, UnitActions.MODIFY.getActionValue());
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}
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LOGGER.info("Commit started");
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if (context.containsKey(IUnitOfWork.INSERT)) {
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commitInsert();
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@Override
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public void registerDeleted(Weapon weapon) {
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LOGGER.info("Registering {} for delete in context.", weapon.getName());
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register(weapon, UnitActions.DELETE.getActionValue());
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}
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if (context.containsKey(IUnitOfWork.MODIFY)) {
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commitModify();
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private void register(Weapon weapon, String operation) {
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var weaponsToOperate = context.get(operation);
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if (weaponsToOperate == null) {
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weaponsToOperate = new ArrayList<>();
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}
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weaponsToOperate.add(weapon);
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context.put(operation, weaponsToOperate);
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}
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if (context.containsKey(IUnitOfWork.DELETE)) {
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commitDelete();
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/**
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* All UnitOfWork operations are batched and executed together on commit only.
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*/
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@Override
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public void commit() {
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if (context == null || context.size() == 0) {
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return;
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}
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LOGGER.info("Commit started");
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if (context.containsKey(UnitActions.INSERT.getActionValue())) {
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commitInsert();
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}
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if (context.containsKey(UnitActions.MODIFY.getActionValue())) {
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commitModify();
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}
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if (context.containsKey(UnitActions.DELETE.getActionValue())) {
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commitDelete();
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}
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LOGGER.info("Commit finished.");
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}
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LOGGER.info("Commit finished.");
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}
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private void commitInsert() {
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var studentsToBeInserted = context.get(IUnitOfWork.INSERT);
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for (var student : studentsToBeInserted) {
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LOGGER.info("Saving {} to database.", student.getName());
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studentDatabase.insert(student);
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private void commitInsert() {
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var weaponsToBeInserted = context.get(UnitActions.INSERT.getActionValue());
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for (var weapon : weaponsToBeInserted) {
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LOGGER.info("Inserting a new weapon {} to sales rack.", weapon.getName());
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weaponDatabase.insert(weapon);
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}
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}
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}
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private void commitModify() {
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var modifiedStudents = context.get(IUnitOfWork.MODIFY);
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for (var student : modifiedStudents) {
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LOGGER.info("Modifying {} to database.", student.getName());
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studentDatabase.modify(student);
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private void commitModify() {
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var modifiedWeapons = context.get(UnitActions.MODIFY.getActionValue());
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for (var weapon : modifiedWeapons) {
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LOGGER.info("Scheduling {} for modification work.", weapon.getName());
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weaponDatabase.modify(weapon);
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}
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}
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}
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private void commitDelete() {
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var deletedStudents = context.get(IUnitOfWork.DELETE);
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for (var student : deletedStudents) {
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LOGGER.info("Deleting {} to database.", student.getName());
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studentDatabase.delete(student);
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private void commitDelete() {
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var deletedWeapons = context.get(UnitActions.DELETE.getActionValue());
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for (var weapon : deletedWeapons) {
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LOGGER.info("Scrapping {}.", weapon.getName());
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weaponDatabase.delete(weapon);
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}
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}
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}
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}
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```
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Finally, here's how we use the `StudentRepository` and `commit` the transaction.
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Here is how the whole app is put together.
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```java
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studentRepository.registerNew(ram);
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studentRepository.registerModified(shyam);
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studentRepository.registerDeleted(gopi);
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studentRepository.commit();
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// create some weapons
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var enchantedHammer = new Weapon(1, "enchanted hammer");
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var brokenGreatSword = new Weapon(2, "broken great sword");
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var silverTrident = new Weapon(3, "silver trident");
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// create repository
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var weaponRepository = new ArmsDealer(new HashMap<String, List<Weapon>>(), new WeaponDatabase());
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// perform operations on the weapons
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weaponRepository.registerNew(enchantedHammer);
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weaponRepository.registerModified(silverTrident);
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weaponRepository.registerDeleted(brokenGreatSword);
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weaponRepository.commit();
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```
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Here is the console output.
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```
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21:39:21.984 [main] INFO com.iluwatar.unitofwork.ArmsDealer - Registering enchanted hammer for insert in context.
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21:39:21.989 [main] INFO com.iluwatar.unitofwork.ArmsDealer - Registering silver trident for modify in context.
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21:39:21.989 [main] INFO com.iluwatar.unitofwork.ArmsDealer - Registering broken great sword for delete in context.
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21:39:21.989 [main] INFO com.iluwatar.unitofwork.ArmsDealer - Commit started
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21:39:21.989 [main] INFO com.iluwatar.unitofwork.ArmsDealer - Inserting a new weapon enchanted hammer to sales rack.
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21:39:21.989 [main] INFO com.iluwatar.unitofwork.ArmsDealer - Scheduling silver trident for modification work.
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21:39:21.989 [main] INFO com.iluwatar.unitofwork.ArmsDealer - Scrapping broken great sword.
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21:39:21.989 [main] INFO com.iluwatar.unitofwork.ArmsDealer - Commit finished.
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```
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## Class diagram
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* To optimize the time taken for database transactions.
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* To send changes to database as a unit of work which ensures atomicity of the transaction.
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* To reduce number of database calls.
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* To reduce the number of database calls.
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## Tutorials
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‎unit-of-work/etc/unit-of-work.ucls

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<?xml version="1.0" encoding="UTF-8"?>
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<class-diagram version="1.2.1" 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.unitofwork.StudentDatabase" project="unit-of-work"
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<class id="1" language="java" name="com.iluwatar.unitofwork.WeaponDatabase" project="unit-of-work"
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file="/unit-of-work/src/main/java/com/iluwatar/unitofwork/StudentDatabase.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="170" y="406"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="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.unitofwork.StudentRepository" project="unit-of-work"
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<class id="4" language="java" name="com.iluwatar.unitofwork.ArmsDealer" project="unit-of-work"
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file="/unit-of-work/src/main/java/com/iluwatar/unitofwork/StudentRepository.java" binary="false"
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corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="377" y="166"/>
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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="5" language="java" name="com.iluwatar.unitofwork.Student" project="unit-of-work"
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<class id="5" language="java" name="com.iluwatar.unitofwork.Weapon" project="unit-of-work"
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file="/unit-of-work/src/main/java/com/iluwatar/unitofwork/Student.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="696" y="130"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"

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

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

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