如何使用 spring 数据 mongodb

问题描述

我们有这些数据：

{ "_id" : ObjectId("5ff9227f0c7f5b1601fcceeb"),"geoHash" : "dr72zc5v7440","customerId" : "abcd"}
{ "_id" : ObjectId("5ff9227f0c7f5b1601fcceec"),"geoHash" : "dr7965kev5r7","customerId" : "abcd" }
{ "_id" : ObjectId("5ff9227f0c7f5b1601fcceed"),"geoHash" : "dr79umt6rksy","customerId" : "abcd" }
{ "_id" : ObjectId("5ff9227f0c7f5b1601fcceee"),"geoHash" : "dr7dqxy2cw43","customerId" : "abcd" }
{ "_id" : ObjectId("5ff9227f0c7f5b1601fcceef"),"geoHash" : "dr7g0czp7xrt","customerId" : "abcd"}
{ "_id" : ObjectId("5ff9227f0c7f5b1601fccef0"),"geoHash" : "dr7gehpyjbv0","customerId" : "abcd"}
{ "_id" : ObjectId("5ff9227f0c7f5b1601fccef1"),"geoHash" : "dr7ujw2u8447","customerId" : "abcd"}
{ "_id" : ObjectId("5ff9227f0c7f5b1601fccef2"),"geoHash" : "dr7uzb9e45ry","customerId" : "abcd" }
{ "_id" : ObjectId("5ff9227f0c7f5b1601fccef3"),"geoHash" : "drkj64f3skv6","customerId" : "abcd" }
{ "_id" : ObjectId("5ff9227f0c7f5b1601fccef4"),"geoHash" : "drkjum50nw4t","customerId" : "abcd" }

Mongo 数据库查询：

db.test.aggregate([{ $match : { "customerId" : "abcd" } },{ "$group": {          "_id": {$substr:["$geoHash",4]},count: { $sum: 1 }         }} ])

如何将此查询转换为 Spring mongo java 代码？以下不起作用：

Aggregationoperation group = Aggregation.group("geoHash")
                .first(StringOperators.Substr.valueOf("geoHash").substring(0,4))
                .as("geoHash")
                .count().as("geoHashCount");

解决方法

使用 Spring Data MongoDB 获得所需内容的一种方法是先使用 ProjectOperation，例如：

根据你的数据集需要返回6条记录，确实如此。

MatchOperation matchOperation = Aggregation
        .match(new Criteria("customerId").is("abcd"));
ProjectionOperation projectionOperation = Aggregation
        .project("geoHash")
        .andExpression("substr(geoHash,4)").as("geoHash");
GroupOperation groupOperation = Aggregation
        .group("geoHash")
        .count().as("count");

Aggregation aggregation = Aggregation
        .newAggregation(matchOperation,projectionOperation,groupOperation);
AggregationResults<Object> aggregationResults
        = mongoTemplate.aggregate(aggregation,"collection_name",Object.class);