[英]Query for : How many elements of an array are matching within a string in mongoDb
假設我的JSON如下所示:
{ "id":0,"keywords":"amount,debited,account,ticket,not,generated,now" }
{ "id":1,"keywords":"how,safe,gocash" }
{ "id":2,"keywords":"how,referral,program,gocash,works" }
如果我的數組像
array =["how","safe","gocash"];
那么我如何在與首先檢查時得到計數? 計數應為零,第二個為第三,第二個為三個。 (這意味着字符串中存在多少個數組元素)
有可能還是應該采用什么方法?
解決此問題的一種方法是,通過添加一個將keywords
保存在數組中的額外字段,需要對架構進行某種形式的修改。 在運行聚合管道以返回與原始字符串匹配的數組元素的所需計數時,此字段變得非常方便。
要添加其他字段,您將需要Bulk API操作來更新集合,如下所示:
var bulk = db.collection.initializeOrderedBulkOp(),
count = 0;
db.collection.find({"keywords": { "$exists": true, "$type": 2 }}).forEach(function(doc) {
var keywordsArray = doc.keywords.split(',');
bulk.find({ "_id": doc._id }).updateOne({
"$set": { "keywordsArray": keywordsArray }
});
count++;
if (count % 100 == 0) {
bulk.execute();
bulk = db.collection.initializeUnorderedBulkOp();
}
});
if (count % 100 != 0) { bulk.execute(); }
上面創建了一個附加字段"keywordsArray"
,這是將keywords
字符串拆分為數組的結果。
手術后,您的樣品采集將具有以下文件:
/* 0 */
{
"_id" : ObjectId("561e24e9ba53a16c763eaab4"),
"id" : 0,
"keywords" : "amount,debited,account,ticket,not,generated,now",
"keywordsArray" : [
"amount",
"debited",
"account",
"ticket",
"not",
"generated",
"now"
]
}
/* 1 */
{
"_id" : ObjectId("561e24e9ba53a16c763eaab5"),
"id" : 1,
"keywords" : "how,safe,gocash",
"keywordsArray" : [
"how",
"safe",
"gocash"
]
}
/* 2 */
{
"_id" : ObjectId("561e24e9ba53a16c763eaab6"),
"id" : 2,
"keywords" : "how,referral,program,gocash,works",
"keywordsArray" : [
"how",
"referral",
"program",
"gocash",
"works"
]
}
進入下一個階段,聚合框架管道,運行以下管道操作,該操作使用$let
, $size
和$setIntersection
運算符得出所需的計數結果:
var array = ["how","safe","gocash"];
db.collection.aggregate([
{
"$project": {
"id": 1, "keywords": 1,
"count": {
"$let": {
"vars": {
"commonToBoth": { "$setIntersection": [ "$keywordsArray", array ] }
},
"in": { "$size": "$$commonToBoth" }
}
}
}
}
])
樣本輸出:
/* 0 */
{
"result" : [
{
"_id" : ObjectId("561e24e9ba53a16c763eaab4"),
"id" : 0,
"keywords" : "amount,debited,account,ticket,not,generated,now",
"count" : 0
},
{
"_id" : ObjectId("561e24e9ba53a16c763eaab5"),
"id" : 1,
"keywords" : "how,safe,gocash",
"count" : 3
},
{
"_id" : ObjectId("561e24e9ba53a16c763eaab6"),
"id" : 2,
"keywords" : "how,referral,program,gocash,works",
"count" : 2
}
],
"ok" : 1
}
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