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Assigned Teams:

Query Optimization
Operating System:
ALL
Steps To Reproduce:
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Enterprise test> db.dropDatabase() Enterprise test> db.test.insert({_id: 1, arr_a: [1, 3]}); Enterprise test> db.test.insert({_id: 2, arr_a: [1, 3]}); Enterprise test> db.test.updateOne({_id: 1}, {$set: {"arr_a.0": 2}}); Enterprise test> db.test.updateOne({_id: 2}, [{$set: {"arr_a.0": 2}}]); Enterprise test> db.test.find() [ { _id: 1, arr_a: [ 2, 3 ] }, { _id: 2, arr_a: [ { '0': 2 }, { '0': 2 } ] } ]
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Enterprise test> db.dropDatabase() Enterprise test> db.test.insert({_id: 1, arr_a: [1, 3]}); Enterprise test> db.test.insert({_id: 2, arr_a: [1, 3]}); Enterprise test> db.test.updateOne({_id: 1}, {$set: { "arr_a.0" : 2}}); Enterprise test> db.test.updateOne({_id: 2}, [{$set: { "arr_a.0" : 2}}]); Enterprise test> db.test.find() [ { _id: 1, arr_a: [ 2, 3 ] }, { _id: 2, arr_a: [ { '0' : 2 }, { '0' : 2 } ] } ]
Confidence Status:
None

The documentation isn't clear that dot notation behaviour with arrays using $set provides very different results than using $set with arrays.

The behaviour is surprising.

duplicates

SERVER-24748 Aggregation does not provide a way to access a specific element of an array

related to

SERVER-24748 Aggregation does not provide a way to access a specific element of an array

SERVER-27442 Positional path component in match language should not act as both an array index and a field name for a single document

Participants:: [DO NOT USE] Backlog - Query Optimization, Asya Kamsky, David Storch, Ross Lawley