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Editorial Team
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Asked: 2026-05-28T04:37:04+00:00

In SQL you can do something like: UPDATE test SET a = b +

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In SQL you can do something like:

UPDATE test SET a = b + c

I am wondering if there is something I can do that is similar in MongoDB. For example something like:

db.test.update({},{$set: {a: b + c}})

However, when I try that it says b and c are not defined (which makes sense). Is there some way I can tell mongo to use the value of fields of the object it is updating? Or do I always need to do it in two steps–first retrieving the fields and then using them to construct the appropriate update statement.

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1 Answer

  1. Editorial Team

    You cannot do that with MongoDB in an update operation. You would need to use something like a map/reduce or db.eval to accomplish it and even then you’re still going to be technically running two queries, one to find and one to update.

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