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How do you query for “is not null” in Mongo?
... according to the docs, $exists currently can't use an index, but $ne can.
Edit: Adding some examples due to interest in this answer
Given these inserts:
db.test.insert({"num":1, "check":"check value"});
db.test.insert({"num":2, "check":null});
db.test.insert({"num":3});
This will return all three ...
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