java - 在 GET 方法中用于过滤对象的可选属性

Question

目前我有一个实体Sneaker定义为

@Entity(name = "sneaker")
public class Sneaker extends Product {

    @Column
    private BigDecimal size;

    @Enumerated(EnumType.STRING)
    @Column
    private BrandType brand;

    ...

    // getters, setters, constructors omitted
}

和一个 @RestController get 方法，该方法接受可选参数以根据数据库对象的属性过滤数据库对象

 @GetMapping
    public ResponseEntity<List<Sneaker>> getSneakers(
            @RequestParam Optional<List<BrandType>> brands,
            @RequestParam Optional<List<BigDecimal>> sizes
    ) {
        List<Sneaker> sneakers;

        if (brands.isPresent() && sizes.isEmpty()) {
            sneakers = sneakerService.getAllByBrands(Util.filterNullItems(brands.get()));
        } else if (brands.isEmpty() && sizes.isPresent()) {
            sneakers = sneakerService.getAllBySize(sizes.get());
        } else if (brands.isPresent() && sizes.isPresent()) {
            sneakers = sneakerService.getAllByBrandAndSize(brands.get(), sizes.get());
        } else {
            sneakers = sneakerService.getAll();
        }

        if (sneakers.isEmpty())
            throw new RuntimeException("No Sneakers were found");

        return ResponseEntity
                .ok(sneakers);
    }

根据给定参数查询数据库的最佳实践是什么？我假设 Controller 中的多个 if else 语句不是最好的方法，因为向对象添加更多属性会呈指数级扩展我的代码并造成困惑。我应该查询所有(或仅通过某些属性)对象并使用流过滤它们 Java 风格吗？

Answer 1

我建议使用org.springframework.data.jpa.domain.Specification

public class SneakerSpecifications {
    public static Specification<Sneaker> sizeIn(Optional<List<BigDecimal>> sizes) {
        return (root, query, builder) -> 
            sizes.isPresent() ? 
            root.get("size").in(sizes.get()) :
            builder.conjunction(); // to ignore this clause
    }

    public static Specification<Sneaker> brandIn(Optional<List<BrandType>> brands) {
        return (root, query, builder) -> 
            brands.isPresent() ? 
            root.get("brand").in(brands.get()) :
            builder.conjunction(); // to ignore this clause
    }
}

然后你的SneakerRepository必须扩展org.springframework.data.jpa.repository.JpaSpecificationExecutor

@Repository
public interface SneakerRepository 
    extends JpaRepository<Sneaker, Long>, JpaSpecificationExecutor<Sneaker> {

}

您的服务方式:

@Service
public class SneakerService {    

   @Autowired
   SneakerRepository repository;

    public List<Sneaker> getSneakers(Optional<List<BrandType>> brands, Optional<List<BigDecimal>> sizes) {
             Specification<Sneaker> spec = 
                 Specifications.where(SneakerSpecifications.brandIn(brands))
                 .and(SneakerSpecifications.sizeIn(sizes));

             return repository.findAll(spec);        
        }
    }

如果您不使用Spring Data Jpa，则可以使用Criteria API或Querydsl使用相同的方法

更多信息here