Unit Of Work

大约 3 分钟

又被称为

工作单元

目的

当一个业务事务完成时，所有的更新都作为一个大的工作单元一次性发送，以最小化数据库的往返次数进行持久化。

解释

现实世界例子

武器商人拥有一个包含武器信息的数据库。
全城的商贩们都在不断地更新这些信息，这导致数据库服务器的负载很高。
为了使负载更易于管理，我们应用了工作单元模式，将许多小的更新批量发送。

用直白的话来说

工作单元将许多小的数据库更新合并成一个批次。
以优化往返次数。

MartinFowler.comopen in new window 中说

维护一个受业务事务影响的对象列表。
并协调写出更改和解决并发问题。

编程样例

以下是要持久化到数据库中的 Weapon 的实体。

@Getter
@RequiredArgsConstructor
public class Weapon {
    private final Integer id;
    private final String name;
}

实现的核心是 ArmsDealer 实现了工作单元模式。
它维护了一个需要完成的数据库操作映射 (context) 当调用 commit 时
它会一次性批量应用这些操作。

public interface IUnitOfWork<T> {
    
  String INSERT = "INSERT";
  String DELETE = "DELETE";
  String MODIFY = "MODIFY";

  void registerNew(T entity);

  void registerModified(T entity);

  void registerDeleted(T entity);

  void commit();
}

@Slf4j
@RequiredArgsConstructor
public class ArmsDealer implements IUnitOfWork<Weapon> {

    private final Map<String, List<Weapon>> context;
    private final WeaponDatabase weaponDatabase;

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

    @Override
    public void registerModified(Weapon weapon) {
        LOGGER.info("Registering {} for modify in context.", weapon.getName());
        register(weapon, UnitActions.MODIFY.getActionValue());

    }

    @Override
    public void registerDeleted(Weapon weapon) {
        LOGGER.info("Registering {} for delete in context.", weapon.getName());
        register(weapon, UnitActions.DELETE.getActionValue());
    }

    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);
        }
    }
}

以下描述了整个应用是如何组装起来的。

// 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();

以下是控制台输出。

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.

类图

Unit Of Work

又被称为

目的

解释

类图

应用

教程

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