Java中优化列表元素批量映射与更新策略

private Item getItemManufacturerPriceCodes(Item item) {
    List<ItemPriceCode> itemPriceCodes = item.getItemPriceCodes();

    for(ItemPriceCode ipc : itemPriceCodes) {
        // 问题所在：在循环中执行数据库查询，导致N+1问题
        Optional<ManufacturerPriceCodes> mpc = manufacturerPriceCodesRepository
            .findByManufacturerIDAndPriceCodeAndRecordDeleted(
                item.getManufacturerID(), ipc.getPriceCode(), NOT_DELETED);
        if(mpc.isPresent()) {
            ipc.setManufacturerPriceCode(mpc.get().getName());
        }
    }
    // 过滤掉已删除的ItemPriceCode
    item.getItemPriceCodes().removeIf(ipc -> DELETED.equals(ipc.getRecordDeleted()));
    return item;
}

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Query;
import org.springframework.data.repository.query.Param;
import java.util.List;

public interface ManufacturerPriceCodesRepository extends JpaRepository<ManufacturerPriceCodes, String> {

    /**
     * 根据制造商ID、记录状态和一系列ItemPriceCode，批量查询对应的制造商价格代码名称。
     * 返回结果为List<Object[]>，其中每个Object[]包含ItemPriceCode的ID和对应的制造商价格代码名称。
     *
     * @param manufacturerId 制造商ID
     * @param notDeleted 记录未删除状态标志
     * @param itemPriceCodes 要查询的ItemPriceCode列表
     * @return 包含ItemPriceCode ID和制造商价格代码名称的Object数组列表
     */
    @Query("SELECT ipc.id, mpc.name FROM ManufacturerPriceCodes mpc JOIN mpc.priceCode ipc " +
           "WHERE mpc.manufacturerID = :manufacturerId AND ipc IN :itemPriceCodes AND mpc.recordDeleted = :notDeleted")
    List<Object[]> findMFPNameByIdAndRecordDeletedAndPriceCodes(
            @Param("manufacturerId") String manufacturerId,
            @Param("notDeleted") <Type> notDeleted, // 替换<Type>为实际的类型，例如Boolean或String
            @Param("itemPriceCodes") List<ItemPriceCode> itemPriceCodes);
}

import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

public class ItemService { // 假设这是一个服务类

    private ManufacturerPriceCodesRepository manufacturerPriceCodesRepository;
    // 假设NOT_DELETED和DELETED是常量，例如Boolean.FALSE和Boolean.TRUE
    private static final Boolean NOT_DELETED = Boolean.FALSE;
    private static final Boolean DELETED = Boolean.TRUE;

    // 构造函数注入repository
    public ItemService(ManufacturerPriceCodesRepository manufacturerPriceCodesRepository) {
        this.manufacturerPriceCodesRepository = manufacturerPriceCodesRepository;
    }

    private Item getItemManufacturerPriceCodes(Item item) {
        List<ItemPriceCode> itemPriceCodes = item.getItemPriceCodes();

        // 1. 批量查询：调用自定义Repository方法，一次性获取所有相关数据
        List<Object[]> keyPairs = manufacturerPriceCodesRepository.findMFPNameByIdAndRecordDeletedAndPriceCodes(
                item.getManufacturerID(), NOT_DELETED, itemPriceCodes);

        // 2. 内存映射：将查询结果转换为Map，便于O(1)查找
        // 假设ipc.getId()返回String类型，mpc.getName()返回String类型
        Map<String, String> ipcToMFPNameMap = keyPairs.stream()
                .collect(Collectors.toMap(
                        // 确保类型匹配，如果ID不是String，需要相应调整
                        x -> (String) x[0], // ItemPriceCode ID
                        x -> (String) x[1]  // ManufacturerPriceCodes Name
                ));

        // 3. 高效更新：遍历ItemPriceCode列表，从Map中获取对应值并设置
        itemPriceCodes.forEach(ipc -> {
            // 假设ItemPriceCode有一个getId()方法返回其唯一标识符
            String mfpName = ipcToMFPNameMap.get(ipc.getId());
            if (mfpName != null) {
                ipc.setManufacturerPriceCode(mfpName);
            }
        });

        // 4. 过滤已删除的ItemPriceCode（此步骤与批量更新逻辑独立）
        item.getItemPriceCodes().removeIf(ipc -> DELETED.equals(ipc.getRecordDeleted()));

        return item;
    }
}