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java-ddd-example\n\nこのプロジェクトはDDDの例です。\n\n## 以下がドメインモデルです\n\n- [Money](https://github.com/j5ik2o/java-ddd-example/blob/master/domain/src/main/java/com/github/j5ik2o/ddd_example/domain/Money.java)\n- [BankAccount](https://github.com/j5ik2o/java-ddd-example/blob/master/domain/src/main/java/com/github/j5ik2o/ddd_example/domain/BankAccount.java)\n  - [BankAccountEvent](https://github.com/j5ik2o/java-ddd-example/blob/master/domain/src/main/java/com/github/j5ik2o/ddd_example/domain/BankAccountEvent.java)\n- [BankAccountService](https://github.com/j5ik2o/java-ddd-example/blob/master/domain/src/main/java/com/github/j5ik2o/ddd_example/domain/BankAccountService.java)\n\n## ユビキタス言語とドメインモデル\n\n- お金ドメインモデル\n    - お金はお金を追加できる\n    - お金はお金を差し引ける\n    - お金とお金は比較できる\n- 銀行口座ドメインモデル\n    - 銀行口座から残高を取得できる\n    - 銀行口座に現金での入金および出金イベントを追加できる\n    - 銀行口座に別の口座からの入金イベントを追加できる。もしくは、口座から別の口座への出金イベントを追加できる\n    - 銀行口座の残高は0未満になってはならない\n- 銀行口座ドメインサービス\n    - 銀行口座ドメインサービスは、口座間の送金ができる。\n\n## ドメインコード\n\nドメインモデルを反映した例は以下。\n\n### お金\n\n- お金はお金を追加できる。\n- お金はお金を差し引ける。\n\n```java\nMoney money1 = Money.of(10000);\nMoney money2 = Money.of(10000);\nMoney result = money1.plus(money2).substract(money2);\nSystem.out.println(result);\n```\n\n- お金とお金は比較できる。\n\n```java\nMoney money3 = Money.of(10000);\nMoney money4 = Money.of(20000);\nMoney result = money3.substract(money2);\nif (result.isLessThan(Money.zero())) {\n    System.out.println(\"result is less than zero!\");\n}\n```\n\n### 銀行口座\n\n口座に現金での入金および出金イベントを追加できる。\n\n```java\nBankAccount bankAccount = new BankAccount(1L, ImmutableList.of())\n    .depositCash(Money.of(10000))\n    .withdrawCash(Money.of(10000));\nSystem.out.println(bankAccount);\n```\n\n口座から残高を取得できる。\n\n```java\nBankAccount bankAccount = new BankAccount(1L, ImmutableList.of()).depositCash(Money.of(10000));\nSystem.out.println(bankAccount.getBalance());\n```\n\n口座に別の口座からの入金イベントを追加できる。もしくは、口座から別の口座への出金イベントを追加できる。\n\n```java\npublic final class BankAccountService {\n\n    public static TransferResult transfer(BankAccount to, BankAccount from, Money money) {\n        BankAccount updatedFrom = from.withdrawTo(to, money);\n        BankAccount updatedTo = to.depositFrom(from, money);\n        return new TransferResult(updatedTo, updatedFrom);\n    }\n\n}\n```\n\n口座の残高は0未満になってはならない\n\n```java\n@Value\npublic final class BankAccount {\n\n    // ...\n\n    public static BankAccount of(Long id, List\u003cBankAccountEvent\u003e events) {\n        if (getBalanceByEvents(events).isLessThan(BigDecimal.ZERO)) {\n            throw new IllegalArgumentException(\"total money is less than zero!\");\n        }\n        return new BankAccount(id, events);\n    }\n\n    // ...\n}\n```\n\n### 銀行口座ドメインサービス\n\n銀行口座ドメインサービスは、口座間の送金ができる。\n\n```java\nMoney initialMoney = Money.of(10000);\nBankAccount bankAccount1 = BankAccount.of(IdGenerator.generateId()).depositCash(initialMoney);\nBankAccount bankAccount2 = BankAccount.of(IdGenerator.generateId()).depositCash(initialMoney);\n\nSystem.out.println(\"bankAccount1 = \" + bankAccount1.getBalance());\nSystem.out.println(\"bankAccount2 = \" + bankAccount2.getBalance());\n\nBankAccountService.TransferResult transferResult = BankAccountService.transfer(\n        bankAccount1,\n        bankAccount2,\n        Money.of(10000)\n);\n\nSystem.out.println(\"to = \" + transferResult.getTo().getBalance());\nSystem.out.println(\"from = \" + transferResult.getFrom().getBalance());\n```\n\n## 貧血症オブジェクトにおける、銀行口座間転送の例\n\nこの例は圧倒的に詳細です。メンタルモデルがないため、コードは理解しがたい。\nドメインモデルが変更された場合、コードを変更することも難しい。\n\n```java\npublic static Money getBalance(BankAccount bankAccount){\n    BigDecimal totalAmount = BigDecimal.ZERO;\n    for(BankAccountEvent event : bankAccount.getEvents()) {\n        totalAmount = totalAmount.add(event.getMoney().getAmount());\n    }\n    Money money = new Money();\n    money.setCurrency(bankAccount.getEvents().get(0).getMoney().getCurrency());\n    money.setAmount(totalAmount);\n    return money;\n}\n\n\nMoney baseMoney = new Money();\nbaseMoney.setCurrency(Currency.getInstance(\"JPY\"));\nbaseMoney.setAmount(BigDecimal.valueOf(10000));\n\nBankAccount bankAccount1 = new BankAccount();\nbankAccount1.setId(IdGenerator.generateId());\nList\u003cBankAccountEvent\u003e events1 = Lists.newArrayList();\nBankAccountEvent incrementEvent1 = new BankAccountEvent();\nincrementEvent1.setId(IdGenerator.generateId());\nincrementEvent1.setToBankAccountId(bankAccount1.getId());\nincrementEvent1.setFromBankAccountId(null);\nincrementEvent1.setMoney(baseMoney);\nincrementEvent1.setOccurredAt(ZonedDateTime.now());\nevents1.add(incrementEvent1);\nbankAccount1.setEvents(events1);\n\n\nBankAccount bankAccount2 = new BankAccount();\nbankAccount2.setId(IdGenerator.generateId());\nList\u003cBankAccountEvent\u003e events2 = Lists.newArrayList();\nBankAccountEvent incrementEvent2 = new BankAccountEvent();\nincrementEvent2.setId(IdGenerator.generateId());\nincrementEvent2.setToBankAccountId(bankAccount1.getId());\nincrementEvent2.setFromBankAccountId(null);\nincrementEvent2.setMoney(baseMoney);\nincrementEvent2.setOccurredAt(ZonedDateTime.now());\nevents2.add(incrementEvent2);\nbankAccount2.setEvents(events2);\n\nMoney totalAmount1 = getBalance(bankAccount1);\nMoney totalAmount2 = getBalance(bankAccount2);\n\nSystem.out.println(\"bankAccount1 = \" + totalAmount1);\nSystem.out.println(\"bankAccount2 = \" + totalAmount2);\n\nMoney data = new Money();\ndata.setCurrency(bankAccount1.getEvents().get(0).getMoney().getCurrency());\ndata.setAmount(BigDecimal.valueOf(10000));\n\nBankAccountService.Result result = BankAccountService.moveData(\n        bankAccount1,\n        bankAccount2,\n        data\n);\n\nMoney newTotalAmount1 = getBalance(result.getTo());\nMoney newTotalAmount2 = getBalance(result.getFrom());\n\nSystem.out.println(\"toTotalAmount = \" + newTotalAmount1);\nSystem.out.println(\"fromTotalAmount = \" + newTotalAmount2);\n```\n\n```java\npublic class BankAccountService {\n    @Data\n    public static class Result {\n        private BankAccount to;\n        private BankAccount from;\n    }\n\n    public static Result moveData(BankAccount to, BankAccount from, Money money) {\n        BigDecimal totalAmount = BigDecimal.ZERO;\n        for(BankAccountEvent event : to.getEvents()) {\n            totalAmount = totalAmount.add(event.getMoney().getAmount());\n        }\n        if (totalAmount.compareTo(money.getAmount()) \u003c 0) {\n            throw new IllegalArgumentException(\"total money is less than zero!\");\n        }\n        BankAccountEvent decrementEvent = new BankAccountEvent();\n        decrementEvent.setId(IdGenerator.generateId());\n        decrementEvent.setFromBankAccountId(from.getId());\n        decrementEvent.setToBankAccountId(to.getId());\n        Money negated = new Money();\n        negated.setCurrency(money.getCurrency());\n        negated.setAmount(money.getAmount().negate());\n        decrementEvent.setMoney(negated);\n        decrementEvent.setOccurredAt(ZonedDateTime.now());\n        BankAccount newFrom = new BankAccount();\n        List\u003cBankAccountEvent\u003e newFromEvent = Lists.newArrayList(from.getEvents());\n        newFromEvent.add(decrementEvent);\n        newFrom.setId(from.getId());\n        newFrom.setEvents(newFromEvent);\n\n        BankAccountEvent incrementEvent = new BankAccountEvent();\n        incrementEvent.setId(IdGenerator.generateId());\n        incrementEvent.setFromBankAccountId(from.getId());\n        incrementEvent.setToBankAccountId(to.getId());\n        incrementEvent.setMoney(money);\n        incrementEvent.setOccurredAt(ZonedDateTime.now());\n        BankAccount newTo = new BankAccount();\n        List\u003cBankAccountEvent\u003e newToEvent = Lists.newArrayList(to.getEvents());\n        newToEvent.add(incrementEvent);\n        newTo.setId(to.getId());\n        newTo.setEvents(newToEvent);\n\n        Result result = new Result();\n        result.setFrom(newFrom);\n        result.setTo(newTo);\n        return result;\n\n    }\n\n}\n```\n","project_url":"https://awesome.ecosyste.ms/api/v1/projects/github.com%2Fj5ik2o%2Fjava-ddd-example","html_url":"https://awesome.ecosyste.ms/projects/github.com%2Fj5ik2o%2Fjava-ddd-example","lists_url":"https://awesome.ecosyste.ms/api/v1/projects/github.com%2Fj5ik2o%2Fjava-ddd-example/lists"}