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Aggregation query to find duplicate key values
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| // Desired unique index: | |
| // db.collection.ensureIndex({ firstField: 1, secondField: 1 }, { unique: true}) | |
| db.collection.aggregate([ | |
| { $group: { | |
| _id: { firstField: "$firstField", secondField: "$secondField" }, | |
| uniqueIds: { $addToSet: "$_id" }, | |
| count: { $sum: 1 } | |
| }}, | |
| { $match: { | |
| count: { $gt: 1 } | |
| }} | |
| ]) |
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