How do we update arrays in the MongoDB documents?

$ updates the first element matching the query condition

$[] updates all elements in the array

$[<identifier>] updates elements that match an arrayFilters condition

$each modifier allows adding multiple items with $push or $addToSet.

$position modifier controls where elements are inserted, with zero-based indexing.

$slice modifier limits array size, and $sort orders elements during updates

$ operator restrictions: The $ operator cannot be used with upsert operations (inserts will treat $ as a field name). It also cannot be used with queries that traverse multiple nested arrays [citation:9].

$ operator with $unset: When used with $unset, the $ operator sets the matching element to null rather than removing it from the array [citation:9].

Multiple array matches: Using $ with queries that filter on multiple array fields can produce ambiguous results. Use $[<identifier>] with arrayFilters for clearer behavior [citation:9].

$pullAll limitations: For arrays containing objects, $pullAll may not work as expected due to object comparison semantics. Use $pull with specific query conditions instead [citation:8].

Upsert with positional operators: When using upsert, the query must include an exact equality match on the array field for positional operators to work correctly during insert [citation:3].