場景
按日期統計每日數據的條數,使用MongoTemplate實現按日期分組統計。
實現思路
先看看mongo命令怎麼實現:
db.collection.aggregate([
{
$project: {date: {$dateToString: {format: "%Y-%m-%d", date: "$createTime"}}}
},
{$group: {_id: "$date", count: {$sum: 1}}},
{$project: {count: 1, _id: 0, date: "$_id"}},
{$sort: {"date": 1}}
])
對應的 java 實現:
Aggregation aggregation = Aggregation.newAggregation(
Aggregation.project("createTime").and(DateOperators.DateToString.dateOf("createTime").toString("%Y-%m-%d")).as("date"),
Aggregation.group("date").count().as("count"),
Aggregation.project("date", "count").and("date").previousOperation(),
Aggregation.sort(Sort.Direction.ASC, "date")
);
AggregationResults<StatisticDayDTO> result = mongoTemplate.aggregate(aggregation, collectionName, StatisticDayDTO.class);
List<StatisticDayDTO> list = result.getMappedResults();
代碼解釋:
project:顯示哪幾個字段,這裏顯示createTime字段,and..as是把and後的字段重命名爲as後的字段,這裏把createTime處理後重命名爲date
group:分組操作,這裏按date分組,計算數量,結果數量重命名爲count
第二個project:previousOperation方法是把_id重命名爲date(也就是別名)
sort:結果按照date正序排序
collectionName: 集合名稱
爲了更好的理解and…previousOperation方法的含義,這裏解釋下:
去掉第二個project,結果形如[{"count": 3, "_id": "2019-12-13"}]
加上第二個project,結果形如[{"count": 3, "date": "2019-12-13"}]