查询：mongoDb中的字符串中匹配多少个数组元素

Question

Suppose my JSON is like following:

{ "id":0,"keywords":"amount,debited,account,ticket,not,generated,now" }
{ "id":1,"keywords":"how,safe,gocash" }
{ "id":2,"keywords":"how,referral,program,gocash,works" }

If my array is like

array =["how","safe","gocash"];

then how do I get the count that while checking with first; count should be zero, with second three and with third two. (That means how many elements of an array are present in the string)

Is it possible or what approach I should adopt?

Answer 1

One way of solving this would require some form of modification to your schema by adding an extra field that holds the keywords in an array. This field becomes quite handy when running an aggregation pipeline to return the desired count of elements of an array that match the original string.

To add the additional field you would need the Bulk API operations to update the collection as follows:

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(); }

The above creates an additional field "keywordsArray" that is a result of splitting the keywords string to an array.

After the operation your sample collection would have the documents:

/* 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"
    ]
}

On to the next stage, the aggregation framework pipeline, run the following pipeline operation which uses the $let , $size and $setIntersection operators to work out the the desired count result:

var array = ["how","safe","gocash"];
db.collection.aggregate([
    {
        "$project": {
            "id": 1, "keywords": 1,
            "count": {
                "$let": {
                   "vars": {
                      "commonToBoth": { "$setIntersection": [ "$keywordsArray", array ] }
                   },
                   "in": { "$size": "$$commonToBoth" }
                }
            }
        }
    }
])

Sample Output:

/* 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
}