标签：mongodb
db.collection.group()使用JavaScript，它受到了一些性能上的限制。大多数情况下，$ group在Aggregation Pipeline提供了一种具有较少的限制适用的替代。可以通过指定的键的集合中的文档和执行简单的聚合函数。在2.2版本中，返回的数组可以包含最多20000个元素；即最多20000个独特的分组。
我们比较熟悉的group by 的sql语句select key from table groupby key,而mongoDB没提供SQL那样通过Group By就轻松实现数据库的分组功能，我们通过接口来实现的
db.collection.group({ key, reduce, initial[, keyf] [, cond] [, finalize] })
|
key |
作为分组的key |
|
reduce |
一个聚合函数操作文档的分组操作期间。这些函数可以返回一个sum或count。该函数接受两个参数：当前文档和这个群体聚集的结果文档。 |
|
initial |
初始化聚合结果文档变量，为空时自动为每列提供初始变量。 |
|
keyf |
可选。替代的key 字段。指定一个函数创建一个“key object”作为分组的key。使用keyf而是通过group by领域而不是现有的文档域键组。 |
|
cond |
过滤条件 |
|
finalize |
在db.collection.group()返回最终结果之前，此功能可以修改的结果文档或替换的结果文档作为一个整体。 |
/* 0 */
{
"_id" : ObjectId("552a330e05c27486b9b9b650"),
"_class" : "com.mongo.model.Orders",
"onumber" : "002",
"date" : ISODate("2014-01-03T16:03:00Z"),
"cname" : "zcy",
"item" : {
"quantity" : 1,
"price" : 4.0,
"pnumber" : "p002"
}
}
/* 1 */
{
"_id" : ObjectId("552a331d05c275d8590a550d"),
"_class" : "com.mongo.model.Orders",
"onumber" : "003",
"date" : ISODate("2014-01-04T16:03:00Z"),
"cname" : "zcy",
"item" : {
"quantity" : 10,
"price" : 2.0,
"pnumber" : "p001"
}
}
/* 2 */
{
"_id" : ObjectId("552a333105c2f28194045a72"),
"_class" : "com.mongo.model.Orders",
"onumber" : "003",
"date" : ISODate("2014-01-04T16:03:00Z"),
"cname" : "zcy",
"item" : {
"quantity" : 30,
"price" : 4.0,
"pnumber" : "p002"
}
}
/* 3 */
{
"_id" : ObjectId("552a333f05c2b62c01cff50e"),
"_class" : "com.mongo.model.Orders",
"onumber" : "004",
"date" : ISODate("2014-01-05T16:03:00Z"),
"cname" : "zcy",
"item" : {
"quantity" : 5,
"price" : 4.0,
"pnumber" : "p002"
}
}1）我们要对日期和产品编码进行分组，并计算相同的产品的数量
Sql语句：Select date, pnumber,sum(quantity) as total from orders,items group by date, pnumber（少了两张表的关联的条件）
MongoDB：
db.orders.group({
key: { date:1,‘item.pnumber‘:1},
initial : {"total":0},
reduce : function Reduce(doc, out) {
out.total+=doc.item.quantity
} });
结果：
2）实现一天卖出了多少个产品，金额是多少，平均价格是多少
db.orders.group({
key: {date:1},
initial :{"total":0,"money":0},
reduce : function Reduce(doc, out) {
out.total+=doc.item.quantity;
out.money+=doc.item.quantity*doc.item.price;
},
finalize : function Finalize(out) {
out.avg=out.money/out.total
returnout;
}
});
结果：
3）keyf的使用
keyf 对日期进行处理并以作为key来进来分组
db.orders.group({
keyf: function (doc){
return{‘month‘:doc.date.getMonth()+1};
},
initial :{"total":0,"money":0},
reduce : function Reduce(doc, out) {
out.total+=doc.item.quantity;
out.money+=doc.item.quantity*doc.item.price;
},
finalize : function Finalize(out) {
out.avg=out.money/out.total
returnout;
}
});
结果：
1）我们要对日期和产品编码进行分组，并计算相同的产品的数量
<strong> </strong> @Override
public void getGroupCount(String collectionName) {
BasicDBObject key = new BasicDBObject();
key.put("date", 1);
key.put("item.pnumber", 1);
//条件
BasicDBObject cond = new BasicDBObject();
//初始化
BasicDBObject initial = new BasicDBObject();
initial.append("total", 0);
//reduce
String reduce = "function Reduce(doc, out) { " +
" out.total+=doc.item.quantity;" +
"}";
SimpleDateFormat format=new SimpleDateFormat("yyyy-mm-dd");
BasicDBList groupList=(BasicDBList) mongoTemplate.getCollection(collectionName).group(key, cond, initial, reduce);
if(groupList!=null&&groupList.size()>0){
System.out.println("date item.pnumber total");
for(int i=0;i<groupList.size();i++){
BasicDBObject obj=(BasicDBObject) groupList.get(i);
System.out.println(format.format(obj.getDate("date"))+" "+obj.getString("item.pnumber")+" "+obj.getInt("total"));
}
}
}结果：
2）实现一天卖出了多少个产品，金额是多少，平均价格是多少
@Override
public void getGroupAvg(String collectionName) {
BasicDBObject key = new BasicDBObject();
key.put("date", 1);
//条件
BasicDBObject cond = new BasicDBObject();
//初始化
BasicDBObject initial = new BasicDBObject();
initial.append("total", 0);
initial.append("money", 0.0);
//reduce
String reduce = "function Reduce(doc, out) { " +
" out.total+=doc.item.quantity;" +
" out.money+=doc.item.quantity*doc.item.price;" +
"}";
String finalize="function Finalize (out) { " +
" out.avg=out.money/out.total;" +
" return out;" +
"}";
SimpleDateFormat format=new SimpleDateFormat("yyyy-mm-dd");
BasicDBList groupList=(BasicDBList) mongoTemplate.getCollection(collectionName).group(key, cond, initial, reduce, finalize);
if(groupList!=null&&groupList.size()>0){
System.out.println("date total money avg");
for(int i=0;i<groupList.size();i++){
BasicDBObject obj=(BasicDBObject) groupList.get(i);
System.out.println(format.format(obj.getDate("date"))+" "+obj.getInt("total")+" "+obj.getInt("money")+" "+obj.getDouble("avg"));
}
}
}
结果：
标签：mongodb
原文地址：http://blog.csdn.net/congcong68/article/details/45012717
