如何将MongoDB去重国家信息的聚合查询转为Spring Reactive Mongo实现

核心问题说明 #

你原有代码存在两处不符合需求的问题：

• 错误添加了语法不正确且不匹配需求的match过滤条件
• group阶段逻辑和原生查询不一致，没有按countryCode+countryName组合字段分组去重

实现代码 #

场景1：无过滤条件，查询全量去重的国家编码+名称 #

import org.springframework.data.mongodb.core.ReactiveMongoTemplate;
import org.springframework.data.mongodb.core.aggregation.Aggregation;
import org.springframework.stereotype.Repository;
import reactor.core.publisher.Flux;
import static org.springframework.data.mongodb.core.aggregation.Aggregation.*;

@Repository
public class AggregateQueryRepository {
    
    private final ReactiveMongoTemplate reactiveMongoTemplate;

    // 推荐用构造注入替代@Autowired
    public AggregateQueryRepository(ReactiveMongoTemplate reactiveMongoTemplate) {
        this.reactiveMongoTemplate = reactiveMongoTemplate;
    }
    
    public Flux<Location> getAllCountryCodeAndCountry() {
        Aggregation aggregation = newAggregation(
                // 按countryCode和countryName组合分组，天然实现去重，和原生查询逻辑完全一致
                group("countryCode", "countryName"),
                // 将分组后嵌套在_id内的字段映射为Location实体的对应属性
                project()
                        .and("_id.countryCode").as("countryCode")
                        .and("_id.countryName").as("countryName")
        );
        return reactiveMongoTemplate.aggregate(aggregation, "location", Location.class);
    }
}

场景2：支持按传入的countryCode、countryName参数过滤后再去重 #

import org.springframework.data.mongodb.core.ReactiveMongoTemplate;
import org.springframework.data.mongodb.core.aggregation.Aggregation;
import org.springframework.data.mongodb.core.query.Criteria;
import org.springframework.stereotype.Repository;
import reactor.core.publisher.Flux;
import java.util.ArrayList;
import java.util.List;
import static org.springframework.data.mongodb.core.aggregation.Aggregation.*;

@Repository
public class AggregateQueryRepository {
    
    private final ReactiveMongoTemplate reactiveMongoTemplate;

    public AggregateQueryRepository(ReactiveMongoTemplate reactiveMongoTemplate) {
        this.reactiveMongoTemplate = reactiveMongoTemplate;
    }
    
    public Flux<Location> getAllCountryCodeAndCountry(String countryCode, String countryName) {
        List<AggregationOperation> operations = new ArrayList<>();
        // 动态拼接过滤条件，参数不为空时才生效
        Criteria criteria = new Criteria();
        if (countryCode != null) {
            criteria.and("countryCode").is(countryCode);
        }
        if (countryName != null) {
            criteria.and("countryName").is(countryName);
        }
        if (!criteria.getCriteriaObject().isEmpty()) {
            operations.add(match(criteria));
        }
        // 分组去重
        operations.add(group("countryCode", "countryName"));
        // 字段映射
        operations.add(project()
                .and("_id.countryCode").as("countryCode")
                .and("_id.countryName").as("countryName"));

        Aggregation aggregation = newAggregation(operations);
        return reactiveMongoTemplate.aggregate(aggregation, "location", Location.class);
    }
}

注意事项 #

请确保你的Location实体类中存在countryCode和countryName两个属性，且有对应的get/set方法，否则字段映射会失败。

内容的提问来源于stack exchange，提问作者Mira Devi