12.3 编写反应式的MongoDB repository

12.3.1 启用Spring Data MongoDB

1. 添加依赖

如果需要非反应式则添加：

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-mongodb</artifactId>
</dependency>

反应式则添加：

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-mongodb-reactive</artifactId>
</dependency>

1. 添加嵌入式的MongoDB

   <dependency>
    <groupId>de.flapdoodle.embed</groupId>
    <artifactId>de.flapdoodle.embed.mongo</artifactId>
   </dependency>

2. 如果是生产环境，则不使用嵌入式数据库，还需要配置几个属性：

   spring:
   data:
    mongodb:
      host: xxxx
      port: 27018
      username: xxxx
      password: xxxx
      database: xxxx

   12.3.2 将领域对象映射为文档

• @Id: 将某个属性指明为文档的ID
• @Document: 将领域类型声明为要持久化到MongoDB中的文档

• @Field： 指定某个属性持久化到文档中的字段名称

  @Data
  @RequiredArgsConstructor
  @NoArgsConstructor(access = AccessLevel.PRIVATE, force = true)
  @Document(collection = "ingredients")
  public class Ingredient {
    @Id
    private final String id;
    private final String name;
    private final Type type;
    public static enum Type {
        WRAP, PROTEIN, VEGGIES, CHEESE, SAUCE
    }
  }

  @Id可以用到任意Serializable类型的字段上，包括String和Long @Document(collection = “ingredients”): 如果没有特别指定，则会持久化到类名首字母小写（ingredient）的集合中，可以通过collection属性来改变这种行为

@Data
@Document
public class Taco {
    @Id
    private String id;
    @NotNull
    @Size(min = 5, message = "name must be at least 5 characters long")
    private String name;
    private Date createdAt = new Date();
    @Size(min = 1, message = "You must choose at least 1 ingredient")
    private List<Ingredient> ingredients;
}

@Data
@Document
public class Order implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id
    private String id;
    private Date placedAt = new Date();
    @Field("customer")
    private User user;
    private String deliveryName;
    private String deliveryStreet;
    private String deliveryCity;
    private String deliveryState;
    private String deliveryZip;
    private String ccNumber;
    private String ccExpiration;
    private String ccCVV;
    private List<Taco> tacos = new ArrayList<>();
    public void addDesign(Taco design) {
        this.tacos.add(design);
    }
}

12.3.3 编写反应式的MongoDB repository接口

有两种接口选择：ReactiveCrudRepository和ReactiveMongoRepository
他们之间的区别在于：ReactiveMongoRepository提供多个特殊的insert()⽅法，它们针对新⽂档的持久化进⾏了优化，⽽ReactiveCrudRepository依赖save()⽅法来保存新⽂档和已有的⽂档
在数据库初始化完成之后，我们不会频繁地创建配料的⽂档，甚⾄有可能永远不会这样做。因此， ReactiveMongoRepository提供的优化没有太多的⽤处，我们可以让 IngredientRepository扩展ReactiveCrudRepository：

public interface IngredientRepository extends ReactiveCrudRepository<Ingredient, String> {}

为了将Taco持久化为MongoDB中的⽂档，我们定义另⼀个repository。 与配料⽂档不同，我们会频繁创建taco⽂档。因此，ReactiveMongoRepository优化过的insert()⽅法就很有价值了。

public interface TacoRepository extends  ReactiveMongoRepository<Taco, String> {
    Flux<Taco> findByOrderByCreatedAt();
}

public interface OrderRepository extends ReactiveMongoRepository<Order, String> {
}

public interface UserRepository extends ReactiveMongoRepository<User, String> {
    Mono<User> findByUsername(String username);
}