[大数据]2021-09-04

Java+mongodbTemplate聚合查询

第一次使用mongodbTemplate进行聚合查询踩得一些坑，废话不多说直接上代码：`

@ApiModel(value = "JdgParameterRuleDto", description = "测试类")
public class JdgParameterRuleDto implements Serializable {

    private static final long serialVersionUID = -7421289160530155401L;

    /**
     * 主键
     */
    @ApiModelProperty(name = "_id", value = "主键")
    private ObjectId _id;
    /**
     * 附表对应id
     */
    @ApiModelProperty(name = "test_id", value = "附表对应id")
    private String test_id;
    /**
     * 附表对应code
     */
    @ApiModelProperty(name = "par_channel_code", value = "附表对应code")
    private String test_code;
    /**
     * 判读级别（1：一级2：二级3：三级）
     */
    @ApiModelProperty(name = "sts_level", value = "判读级别（1：一级2：二级3：三级）")
    private Integer sts_level;
   
    private List<BasicParameter> basic_parameter;
}

注意事项：1.在java中对应的实体类字段一定要和mongodb中对应的表字段一模一样，否则返回值对象会因为字段名称不一场而查不到值
2.在上述实体类中除了basic_parameter这个List对象其余字段全部为主表字段，附表数据应该用List对象进行接收，否则查询不到相应数据
以下代码为mongodbTemplate的聚合查询代码：

/**
     * 多表联合查询，
     * @param <T>
     * @return
     */
    @Override
    public <T> List<T> relationQueryMoreToOne(Map<String, Object> paramMap, Class<T> entityClass) {
        LookupOperation lookup = LookupOperation.newLookup()
                //从表（关联的表）
                .from("basic_parameter")
                //主表中与从表相关联的字段
                .localField("test_id")
                //从表与主表相关联的字段
                .foreignField("test_id")
                //查询出的从表集合 命名(相当于从表的别名
                .as("basic_parameter");
        Aggregation aggregation = null;
        //主表查询条件可以给可以不给i
        AggregationOperation match = null;
        if(paramMap.get("par_channel_code") != null){
            Criteria ordercri = Criteria.where("par_channel_code").is(paramMap.get("par_channel_code").toString());
            match = Aggregation.match(ordercri);
            aggregation = Aggregation.newAggregation(match,lookup);
        }
        //次表查询条件可以给可以不给
        AggregationOperation match1 = null;
        if(paramMap.get("subsys_code") != null){
            Criteria ordercri1 = Criteria.where("subsys_code").is(paramMap.get("subsys_code").toString());
            match1 = Aggregation.match(ordercri1);
        }
        //查询条件
        if (match != null && match1 != null){
            aggregation = Aggregation.newAggregation(match,lookup,match1);
        }else if(match == null && match1 == null){
            aggregation = Aggregation.newAggregation(lookup);
        }else if(match != null && match1 == null){
            aggregation = Aggregation.newAggregation(match,lookup);
        }else if(match == null && match1 != null){
            aggregation = Aggregation.newAggregation(lookup,match1);
        }
//        List<AggregationOperation> operations = new ArrayList<>();
//        operations.add(lookup);
//        aggregation = Aggregation.newAggregation(operations);
//		entityClass这个参数为返回值对象即上边的JdgParameterRuleDto 
        AggregationResults<T> studentAggregation = mongoTemplate.aggregate(aggregation, "jdg_parameter_rule", entityClass);
        return (List<T>) studentAggregation.getMappedResults();
    }

以为就是mongodbTemplate的聚合查询，第一次写帖子，不喜勿喷。