Use `$addToSet` to avoid duplicates.
Section: Arrays and positional updates
Append only if missing
javascript
javascript
db.users.updateOne({ _id: 1 }, { $addToSet: { tags: "beta" } })Explanation
Great for tag or role arrays where uniqueness matters.
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Related commands
Same sheet · prioritizing Arrays and positional updates
Update the first matching array element
Use the positional `$` operator.
Target specific nested elements with arrayFilters
Update matching array elements with named filters.