跨索引获取数组字段的不同聚合
为了获得跨索引的数组字段的独特聚合，让我们举一个例子并创建包含一些文档的集合。
以下是使用文档创建集合的查询
> db.distinctAggregation.insertOne({"UserName":"Larry","UserPost":["Hi","Hello"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c98aefb330fd0aa0d2fe4c6")
}
> db.distinctAggregation.insertOne({"UserName":"Chris","UserPost":["Hi","Good Morning"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c98af0a330fd0aa0d2fe4c7")
}
> db.distinctAggregation.insertOne({"UserName":"Robert","UserPost":["Awesome"]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c98af1e330fd0aa0d2fe4c8")
}以下是在find()方法的帮助下显示集合中所有文档的查询
> db.distinctAggregation.find().pretty();
这将产生以下输出
{
"_id" : ObjectId("5c98aefb330fd0aa0d2fe4c6"),
"UserName" : "Larry",
"UserPost" : [
"Hi",
"Hello"
]
}
{
"_id" : ObjectId("5c98af0a330fd0aa0d2fe4c7"),
"UserName" : "Chris",
"UserPost" : [
"Hi",
"Good Morning"
]
}
{
"_id" : ObjectId("5c98af1e330fd0aa0d2fe4c8"),
"UserName" : "Robert",
"UserPost" : [
"Awesome"
]
}以下是在数组字段上创建索引的查询
> db.distinctAggregation.ensureIndex({"UserPost":1});
{
"createdCollectionAutomatically" : false,
"numIndexesBefore" : 1,
"numIndexesAfter" : 2,
"ok" : 1
}以下是查询以获取跨索引的数组字段的不同集合的查询
> db.distinctAggregation.distinct("UserPost");这将产生以下输出
[ "Awesome", "Good Morning", "Hello", "Hi" ]