SpringBoot2.1.9 MongoDB的聚合连接

 LookupOperation lookupOperation= LookupOperation.newLookup().
                from(AdminRepository.instance().getTableName()).  //关联从表名
                localField(User.Fields.name).     //主表关联字段
                foreignField(Admin.Fields.name).//从表关联的字段
                as("adminInfo");   //查询结果名

        Criteria left = Criteria.where(User.Fields.city).exists(true)
                .andOperator(Criteria.where(User.Fields.age).gte(18),
                        Criteria.where(User.Fields.age).lt(65));

        Criteria right = Criteria.where("adminInfo.0").exists(true).and("adminInfo.0.admin").is(1);


        GroupOperation group = Aggregation.group(User.Fields.city).first(User.Fields.age).as("firstAge")
                .avg(User.Fields.age).as("avgAge").addToSet(User.Fields.age).as("ageList")
                .count().as("count").max(User.Fields.age).as("maxAge")
                .push(User.Fields.age).as("ageField");

        ProjectionOperation projectionOperation = Aggregation.project("_id")
                .and("adult").applyCondition(ConditionalOperators.Cond.when(Criteria.where("firstAge").gt(12))
                        .then(1).otherwise(0));
        Aggregation aggregation = Aggregation.newAggregation(Aggregation.match(left), lookupOperation,
                Aggregation.match(right),  Aggregation.unwind("adminInfo", true), group,
                projectionOperation);

        List<Map> results = this.getMongoOperations().aggregate(aggregation, this.getTableName(), Map.class).getMappedResults();

一、聚合

（1）匹配

Aggregation.match(left)

（2）分组

   GroupOperation group = Aggregation.group(User.Fields.city).first(User.Fields.age).as("age")
                .avg(User.Fields.age).as("avgAge").addToSet(User.Fields.age).as("ageList")
                .count().as("count").max(User.Fields.age).as("maxAge")
                .push(User.Fields.age).as("ageField");

（3）投影

ProjectionOperation projectionOperation = Aggregation.project("_id")
                .and("adult").applyCondition(ConditionalOperators.Cond.when(Criteria.where("firstAge").gt(12))
                        .then(1).otherwise(0));

（4）扁平化数组

Aggregation.unwind("adminInfo", true)

二、连接

 LookupOperation lookupOperation= LookupOperation.newLookup().
                from(AdminRepository.instance().getTableName()).  //关联从表名
                localField(User.Fields.name).     //主表关联字段
                foreignField(Admin.Fields.name).//从表关联的字段
                as("adminInfo");   //查询结果名