在SQL语句中如要做统计一般是这种方式：
SELECT ..,SUM(1)
FROM ..
WHERE ..
GROUP BY ..
HAVING ..
SORT ..
在MONGODB中的架构图
在SPRING DATA MONGODB中是这样写的：
public class VideoRepositoryImpl implements VideoRepositoryCustom{
private static Logger logger = LoggerFactory.getLogger(VideoRepositoryImpl.class);
@Autowired
private MongoTemplate mongoTemplate;
public List<Cat1UpdateCount> getVideoWithUpdateFrag(List<String> importantCat1List) {
logger.info(new Date().toString());
/**
* db.videos.aggregate(
[
{ $match: { "frags.isnew" : true } },
{ $unwind: "$frags" },
{ $match: { "frags.isnew" : true } },
{ $group: {
_id: {cat1:"$cat1"},
count: { $sum: 1 },
publishdate2: { $max: "$publishdate"}
}
}
]
)
*/
Aggregation agg = newAggregation(
project("frags","cat1","publishdate"),//挑选所需的字段
match(
Criteria.where("frags.isnew").is(Boolean.TRUE)
.and("cat1").in(importantCat1List)
),//筛选符合条件的记录
unwind("frags"),//如果有MASTER-ITEM关系的表，需同时JOIN这两张表的，展开子项LIST，且是内链接，即如果父和子的关联ID没有的就不会输出
match(Criteria.where("frags.isnew").is(Boolean.TRUE)),
group("cat1")//设置分组字段
.count().as("updateCount")//增加COUNT为分组后输出的字段
.last("publishdate").as("publishDate"),//增加publishDate为分组后输出的字段
project("publishDate","cat1","updateCount")//重新挑选字段
.and("cat1").previousOperation()//为前一操作所产生的ID FIELD建立别名
);
AggregationResults<Cat1UpdateCount> results = mongoTemplate.aggregate(agg, Video.COLLECTION_NAME, Cat1UpdateCount.class);
List<Cat1UpdateCount> cat1UpdateCountList = results.getMappedResults();
return cat1UpdateCountList;
}
}
其中frags的数据类型是LIST
Cat1UpdateCount.java
import java.io.Serializable;
public class Cat1UpdateCount implements Serializable{
private static final long serialVersionUID = 4240876746984930098L;
private String cat1;
private int updateCount;
private String publishDate;
public String getCat1() {
return cat1;
}
public void setCat1(String cat1) {
this.cat1 = cat1;
}
public int getUpdateCount() {
return updateCount;
}
public void setUpdateCount(int updateCount) {
this.updateCount = updateCount;
}
public String getPublishDate() {
return publishDate;
}
public void setPublishDate(String publishDate) {
this.publishDate = publishDate;
}
public String toString() {
return "Cat1UpdateCount [cat1=" + cat1 + ", updateCount=" + updateCount
+ ", publishDate=" + publishDate + "]";
}
}
参考：
http://docs.spring.io/spring-data/data-mongodb/docs/current/reference/htmlsingle/#mongo.grouphttp://docs.mongodb.org/manual/reference/operator/aggregation/group/http://docs.mongodb.org/manual/reference/sql-aggregation-comparison/