The difference between $push and $addToSet is:

The correct answer is B. $addToSet adds the item to the field only if it does not exist already; while $push pushes the item. B is correct because $addToSet is specifically designed to prevent duplicates - it only appends an item to an array field if that exact value doesn't already exist, whereas $push always appends regardless of duplicates. A is wrong because both operators will create the array fiel

MongoDB Fundamentals

Question

Options

A$addToSet needs the fields to be already present while $push will work even if the field is not
B$addToSet adds the item to the field only if it does not exist already; while $push pushes the item
C$addToSet adds the item to the field only if the new item is of the same datatype
DThere is no major difference between them. $addToSet is a deprecated version of $push.

How the community answered

(50 responses)

B
94% (47)
C
4% (2)
D
2% (1)

Explanation

B is correct because $addToSet is specifically designed to prevent duplicates - it only appends an item to an array field if that exact value doesn't already exist, whereas $push always appends regardless of duplicates. A is wrong because both operators will create the array field if it doesn't exist yet - neither requires the field to be pre-existing. C is wrong because $addToSet checks for value equality, not datatype matching; it simply performs a duplicate check on the whole value. D is wrong because these are two distinct, actively-used operators with genuinely different behavior - neither is deprecated.

Memory tip: Think of $addToSet like a mathematical set - sets never contain duplicates, so the operator enforces that rule. $push is just a plain array push with no uniqueness guarantee.

Topics

#$push#$addToSet#array operators#update operators

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