在MongoDB中按其他字段查找值分组？
要按另一个字段分组，请使用$group和$project。首先让我们创建一个包含文档的集合-
> db.demo374.insertOne(
... {
...
... "Name" : "Chris",
... "HobbyDetails" : [
... "Reading Book",
... "Playing Football"
... ],
... "CountryName" : "US"
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5e5a04402ae06a1609a00b04")
}
> db.demo374.insertOne(
... {
...
... "Name" : "Chris",
... "HobbyDetails" : [
... "Browsing Internet",
... "Playing Football"
... ],
... "CountryName" : "US"
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5e5a04402ae06a1609a00b05")
}在find()方法的帮助下显示集合中的所有文档-
> db.demo374.find();
这将产生以下输出-
{ "_id" : ObjectId("5e5a04402ae06a1609a00b04"), "Name" : "Chris", "HobbyDetails" : [ "Reading Book", "Playing Football" ], "CountryName" : "US" }
{ "_id" : ObjectId("5e5a04402ae06a1609a00b05"), "Name" : "Chris", "HobbyDetails" : [ "Browsing Internet", "Playing Football" ], "CountryName" : "US" }以下是在MongoDB中按另一个字段查找值分组的查询-
> db.demo374.aggregate([
... {$match : { "CountryName" : "US"}},
... {$group : {"_id" : "$Name", "HobbyDetails" : {$addToSet : "$HobbyDetails"}}},
... {$project : {"_id" : 0, "Name" : "$_id", "HobbyDetails" : {$reduce : {input : "$HobbyDetails", initialValue : [], in: { $concatArrays : ["$$value", "$$this"] }}}}}
... ]).pretty()这将产生以下输出-
{
"Name" : "Chris",
"HobbyDetails" : [
"Browsing Internet",
"Playing Football",
"Reading Book",
"Playing Football"
]
}