重构零食实体

Snack只有三种类型，不允许出现其它类型：

package com.lugew.springbootddd;
import lombok.Getter;
import lombok.Setter;
/**
 * @author 夏露桂
 * @since 2021/6/16 10:45
 */
@Getter
@Setter
public class Snack extends AggregateRoot {
    public static Snack None = new Snack(0, "None");
    public static Snack Chocolate = new Snack(1, "Chocolate");
    public static Snack Soda = new Snack(2, "Soda");
    public static Snack Gum = new Snack(3, "Gum");
    private String name;
    private Snack(long id, String name) {
        this.id = id;
        this.name = name;
    }
    public SnackDto convertToSnackDto() {
        SnackDto snackDto = new SnackDto();
        snackDto.setId(id);
        snackDto.setName(name);
        return snackDto;
    }
}

随后将测试中的new Snack(“Some snack”) 替换为Chocolate。

package com.lugew.springbootddd.snackmachine;
import com.lugew.springbootddd.Snack;
import com.lugew.springbootddd.SnackPile;
import org.junit.jupiter.api.Test;
import static com.lugew.springbootddd.snackmachine.Money.*;
import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertThrows;
/**
 * @author 夏露桂
 * @since 2021/6/9 18:12
 */
public class SnackMachineTest {
    @Test
    public void return_money_empties_money_in_transaction() {
        SnackMachine snackMachine = new SnackMachine();
        snackMachine.insertMoney(Dollar);
        snackMachine.returnMoney();
        assertEquals(snackMachine.getMoneyInTransaction(), 0, 0);
    }
    @Test
    public void inserted_money_goes_to_money_in_transaction() {
        SnackMachine snackMachine = new SnackMachine();
        snackMachine.insertMoney(Cent);
        snackMachine.insertMoney(Dollar);
        assertEquals(snackMachine.getMoneyInTransaction(), 1.01f, 0);
    }
    @Test
    public void cannot_insert_more_than_one_coin_or_note_at_a_time() {
        SnackMachine snackMachine = new SnackMachine();
        Money twoCent = Money.add(Cent, Cent);
        assertThrows(IllegalStateException.class, () -> {
            snackMachine.insertMoney(twoCent);
        });
    }
    @Test
    public void buySnack_trades_inserted_money_for_a_snack() {
        SnackMachine snackMachine = new SnackMachine();
        snackMachine.loadSnacks(1, new SnackPile(Snack.Chocolate, 10, 1));
        snackMachine.insertMoney(Dollar);
        snackMachine.buySnack(1);
        assertEquals(snackMachine.getMoneyInTransaction(), Money.None.getAmount());
        assertEquals(snackMachine.getMoneyInside().getAmount(), 1, 0.5);
        assertEquals(snackMachine.getSnackPile(1).getQuantity(), 9);
    }
    @Test
    public void cannot_make_purchase_when_there_is_no_snacks() {
        SnackMachine snackMachine = new SnackMachine();
        assertThrows(IllegalStateException.class, () -> {
            snackMachine.buySnack(1);
        });
    }
    @Test
    public void cannot_make_purchase_if_not_enough_money_inserted() {
        SnackMachine snackMachine = new SnackMachine();
        snackMachine.loadSnacks(1, new SnackPile(Snack.Chocolate, 1, 2));
        snackMachine.insertMoney(Dollar);
        assertThrows(IllegalStateException.class, () -> {
            snackMachine.buySnack(1);
        });
    }
    @Test
    public void snack_machine_returns_money_with_highest_denomination_first() {
        SnackMachine snackMachine = new SnackMachine();
        snackMachine.loadMoney(Dollar);
        snackMachine.insertMoney(Quarter);
        snackMachine.insertMoney(Quarter);
        snackMachine.insertMoney(Quarter);
        snackMachine.insertMoney(Quarter);
        snackMachine.returnMoney();
        assertEquals(snackMachine.getMoneyInside().getQuarterCount(), 4);
        assertEquals(snackMachine.getMoneyInside().getOneDollarCount(), 0);
    }
    @Test
    public void after_purchase_change_is_returned() {
        SnackMachine snackMachine = new SnackMachine();
        snackMachine.loadSnacks(1, new SnackPile(Snack.Chocolate, 1,
                0.5f));
        snackMachine.loadMoney(
                new Money(0, 10, 0, 0, 0, 0)
        );
        snackMachine.insertMoney(Dollar);
        snackMachine.buySnack(1);
        assertEquals(snackMachine.getMoneyInside().getAmount(), 1.5, 0);
        assertEquals(snackMachine.getMoneyInTransaction(), 0, 0);
    }
    @Test
    public void cannot_buy_snack_if_not_enough_change() {
        SnackMachine snackMachine = new SnackMachine();
        snackMachine.loadSnacks(1, new SnackPile(Snack.Chocolate, 1, 0.5f));
        snackMachine.insertMoney(Dollar);
        assertThrows(IllegalStateException.class, () -> {
            snackMachine.buySnack(1);
        });
    }
}

此外Slot构造器也可以优化：

public class Slot extends Entity {
    public Slot(SnackMachine snackMachine, int position) {
    this.snackMachine = snackMachine;
    this.position = position;
    this.snackPile = new SnackPile(Snack.None, 0, 0);
    }
}

再次重构：

public class SnackPile extends ValueObject<SnackPile> {
    public static SnackPile Empty = new SnackPile(Snack.None, 0, 0f);
}

最终结果：

package com.lugew.springbootddd;
import com.lugew.springbootddd.snackmachine.SnackMachine;
import lombok.Getter;
import lombok.Setter;
/**
 * @author 夏露桂
 * @since 2021/6/16 10:47
 */
@Getter
@Setter
public class Slot extends Entity {
    private SnackPile snackPile;
    private SnackMachine snackMachine;
    private int position;
    public Slot() {
    }
    public Slot(SnackMachine snackMachine, int position) {
        this.snackMachine = snackMachine;
        this.position = position;
        this.snackPile = SnackPile.Empty;
    }
    public SlotDto convertToSlotDto() {
        SlotDto slotDto = new SlotDto();
        slotDto.setId(id);
        slotDto.setPosition(position);
        slotDto.setPrice(snackPile.getPrice());
        slotDto.setQuantity(snackPile.getQuantity());
        slotDto.setSnackDto(snackPile.getSnack().convertToSnackDto());
        return slotDto;
    }
    public SnackPile getSnackPile() {
        return snackPile;
    }
    public void setSnackPile(SnackPile snackPile) {
        this.snackPile = snackPile;
    }
    public SnackMachine getSnackMachine() {
        return snackMachine;
    }
    public void setSnackMachine(SnackMachine snackMachine) {
        this.snackMachine = snackMachine;
    }
    public int getPosition() {
        return position;
    }
    public void setPosition(int position) {
        this.position = position;
    }
}

👆持续迭代在DDD中十分常见。

Snack类型的校验可在集成测试中验证。