CODEWITHSUNDEEP
mongodb
Nikita Platonenko
Nikita Platonenko

Reputation: 702

How to find mongo documents with a same field

I have a mongo collection, and I need to find documents in this collection, in which fields name and address are equal.

I have searched a lot, I could only find MongoDb query condition on comparing 2 fields and MongoDB: Unique and sparse compound indexes with sparse values, but in these questions they are looking for documents in which field a = field b, but I need to find document1.a == document2.a

Upvotes: 46

Views: 45105

Answers (1)

Stennie
Stennie

Reputation: 65403

You can find duplicates using the Aggregation Framework and $group.

Example data set up:

// Batch insert some test data
db.mycollection.insert([
    {a:1, b:2, c:3},
    {a:1, b:2, c:4},
    {a:0, b:2, c:3},
    {a:3, b:2, c:4}
])

Aggregation query:

db.mycollection.aggregate(
    { $group: { 
        // Group by fields to match on (a,b)
        _id: { a: "$a", b: "$b" },

        // Count number of matching docs for the group
        count: { $sum:  1 },

        // Save the _id for matching docs
        docs: { $push: "$_id" }
    }},

    // Limit results to duplicates (more than 1 match) 
    { $match: {
        count: { $gt : 1 }
    }}
)

Example output:

{
    "result" : [
        {
            "_id" : {
                "a" : 1,
                "b" : 2
            },
            "count" : 2,
            "docs" : [
                ObjectId("5162b2e7d650a687b2154232"),
                ObjectId("5162b2e7d650a687b2154233")
            ]
        }
    ],
    "ok" : 1
}

Upvotes: 120

Related Questions