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Type:
Investigation
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Resolution: Unresolved
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Priority:
Major - P3
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None
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Affects Version/s: None
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Component/s: None
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None
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Developer Tools
$merge operation used to fail when encountering null or missing values in fields that merge is preformed on: https://www.mongodb.com/docs/manual/reference/operator/aggregation/merge/#std-label-merge-on
Every $merge must be supported by a unique index.
After this change we allow "on" fields to be null/missing if supporting index is NOT sparse.
If supporting index is sparse, the error would be the same.
We still don't allow arrays in "on" fields.
One important difference is some customers may expect $merge to fail on null and handle this error in their code, but now this operation will just work.
Description of Linked Ticket
In Mongo 4.4, shard keys can be missing, see https://docs.mongodb.com/manual/core/sharding-shard-key/#shard-key-missing
This works fine for insert of documents, however merge in aggregation-framework is failing:
db = db.getSiblingDB("mip") db.createCollection("sharded_col") sh.enableSharding("mip") sh.shardCollection("mip.sharded_col", { tsi: 1 }) db.sharded_col.insertOne({ a: 1 }) db.sharded_col.aggregate([ { $set: { a: 2 } }, { $unset: "_id" }, { $merge: { into: "sharded_col" } } ]) { "ok" : 0.0, "errmsg" : "$merge write error: 'on' field 'tsi' cannot be missing, null, undefined or an array", "code" : NumberInt(51132), "codeName" : "Location51132", "operationTime" : Timestamp(1601372348, 4), "$clusterTime" : { "clusterTime" : Timestamp(1601372351, 40), "signature" : { "hash" : BinData(0, "wv5eJ/xcJoaS1m14aJeoSA3WSqo="), "keyId" : NumberLong(6854861305854033921) } } }
If MongoDB permits missing shard key then it should also apply for merge.
- depends on
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SERVER-51207 $merge not working without shard-key
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- Closed
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