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Type:
Bug
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Resolution: Fixed
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Priority:
Major - P3
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Affects Version/s: None
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Component/s: None
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None
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Query Execution
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Fully Compatible
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ALL
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v8.2, v8.0
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While implementing Django ORM compatibility, I found that `$$NOW` becomes unavailable after introducing a $unionWith stage. This appears inconsistent with other pipeline stages, since `$$NOW` works normally if it is referenced before `$unionWith` or stored using `$set`.
Steps to Reproduce
Pipeline that fails:
[
{ $match: { num_awards: { $gt: 3 } } },
{ $group: { _id: null, total: { $sum: "$duration" } } },
{ $unionWith: { pipeline: [ { $documents: [ {} ] } ] } },
{ $project: { value: { $ifNull: ["$total", { $subtract: ["$$NOW", "$$NOW"] }] } } }
]
pymongo.errors.OperationFailure: PlanExecutor error during aggregation :: caused by :: Builtin variable '$$NOW' is not available, full error: {'ok': 0.0, 'errmsg': "PlanExecutor error during aggregation :: caused by :: Builtin variable '$$NOW' is not available", 'code': 51144, 'codeName': 'Location51144', '$clusterTime': {'clusterTime': Timestamp(1763611140, 562), 'signature': {'hash': b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00', 'keyId': 0}}, 'operationTime': Timestamp(1763611140, 562)}
Pipeline that works (when storing `$$NOW` beforehand):
[
{ $set: { __now: "$$NOW" } },
{ $match: { num_awards: { $gt: 3 } } },
{ $group: { _id: null, total: { $sum: "$duration" } } },
{ $unionWith: { pipeline: [ { $documents: [ {} ] } ] } },
{ $project: { value: { $ifNull: ["$total", { $subtract: ["$$NOW", "$$NOW"] }] } } }
]
MongoDB Version
8.0.11
- related to
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- Needs Scheduling
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