Use $not or $ne in update query - mongodb

Question

Should I use $not or $ne in the query:
Mytable.update({ TheThing: Thing,
'UpdatedInfo.NewInfo': {$ne: ThisNewestInfo} }, {
$push: {
UpdatedInfo: {
TheDate: ThisDate,
NewInfo: ThisNewestInfo,
Past: OriginalInfo
}
}
},
function (err, result) {
if (err){
throw new Error(err.message);
}
}
If I only want to update the document when ThisNewestInfo is not already present in UpdatedInfo array, in NewInfo object element. Trying to understand the difference between $not and $ne.
And also:
If the document does not contain UpdatedInfofield in the beginning? How should I change the update query above? Meaning that if UpdatedInfodoes not exists it adds UpdatedInfo, and later on, say next day, checks if ThisNewestInfois not already present when updating document again.

Answer 1

It depends on your collection actually.
The main different between $ne and $not in this scenario is that, $not performs a logical disjunction. That is if your document didn't had an UpdatedInfo field, using $not would have pushed the document while using $ne nothing would have happened to that document.
So if all your document of collection has UpdatedInfo field, its better to go with $ne.
Edit
Based on your edit you mentioned UpdatedInfo might not be present in document. In such cases you should use $not. $ne wont be able to update docs that doesn't have UpdatedInfo field.
Remember like this: $not checks for presence of key as well as value, while $ne checks only for value and ignores document that doesn't have the particular key in query.