See included reproducer. In a $project stage like {$project: {a: "$meta", b: "$a"}}, the "$a" expression should only be able to reference a value in the original document passed to the $project stage. For time-series collections, if it references the name of a different projection field, where that field references the meta field value, then it is populated with the metadata value as well.
- related to
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SERVER-66570 Timeseries pushes down metaField-projections that can change semantics
- Closed