$match description does not say anything about sorting

[gregsdennis]

The docs for $match does say anything about sorting, and yet there is this test:

title:    $match, 2 matches, ordered by lexcial sorting of property names
context:  {cond: 3}
template: {$match: {'cond == 3': 2, 'cond == 5': 3, 'cond < 5 && cond > 0': 4, 'true': 17}}
result:   [4, 2, 17]

Also, what is the point of sorting in this case? If anything, shouldn't the results be sorted by the order they are in the template (which, depending on the language you're using, may be indeterministic).

[djmitche]

As you mentioned, JSON data structures do not define an order on keys in an object, so it's impossible to order conditions as they were given in the template. But, we want the behavior to be deterministic. So the only alternative is to sort them.

This was kind of a flaw in $match, which IIRC is why $switch was introduced. $switch enforces that at most one arm matches, so the order in which they are checked does not matter.

[djmitche]

(The $match docs should mention the sorting!)