我开始学习mongoDb的性能改进。而且我有一个基于问题的汇总功能。我创建了一个包含3个字段产品,颜色和年份的基本测试集合:
{
"product" : "car",
"colour" : "red",
"year" : "2019"
}
{
"product" : "car",
"colour" : "black",
"year" : "2018"
}
{
"product" : "bike",
"colour" : "blue",
"year" : "2014"
}
{
"product" : "train",
"colour" : "black",
"year" : "2019"
}
{
"product" : "ship",
"colour" : "red",
"year" : "2018"
}
{
"product" : "car",
"colour" : "red",
"year" : "2016"
}
{
"product" : "car",
"colour" : "blue",
"year" : "2015"
}
{
"product" : "bike",
"colour" : "white",
"year" : "2014"
}
{
"product" : "train",
"colour" : "red",
"year" : "2016"
}
{
"product" : "ship",
"colour" : "red",
"year" : "2015"
}
由于性能问题,我希望将facet用于单个聚合阶段:
db.getCollection('test').aggregate([
{
"$match":{
"colour":"red"
}
},
{
"$facet": {
"cntOfReds":[
{"$group":{"_id": "$product", "count": {"$sum": 1}}}
],
"cntOfRedsIn2015":[
{"$match" :{"year": "2015"}},
{"$group": {"_id": "$year", "count": {"$sum": 1}}}
]
} }
])
我们如何使用mgo.v2在golang上实现相同的查询并将结果设置为struct?
使用mgo,您必须将一系列文档传递给Pipe
:
p:=collection.Pipe([]bson.M{
{"$match": bson.M{"colour":"red"}},
{"$facet": bson.M{ "cntOfReds":[]bson.M{{"$group":{"_id": "$product", "count": bson.M{"$sum":1}}}}},
"cntOfRedsIn2015": ...
然后,运行管道并获得结果:
p.All(&results)
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我来说两句