Details
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Task
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Resolution: Duplicate
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Major - P3
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Description
We need an explicit explanation of the difference between $<fieldname> and $<operator> in aggregation. Something similar to this from Kristina:
The "$fieldname" syntax is used to refer to fieldname’s value in the
aggregation framework. For example, "$age" would be replaced with
the contents of the age field (and probably be a number, not a string)
and "$tags.3" would be replaced with the fourth element of the tags
array. Thus, "$_id" is replaced by the "_id" field of each document
coming through the pipeline.