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b5a0613f85
Our cursor interface has no nextObject method, so there's no point in
having a rewind method. Its major effect is ensuring that
fetch/forEach/map return no documents if you've already called one of
them once. It's not clear why this is actually useful to anybody.
rewind is kept around as a no-op; if we later implement nextObject, we
can make rewind do something, but we still presumably would auto-rewind
before fetch/forEach/map.
In minimongo, remove the db_objects cache inside each cursor. The only
actual use of this cache was that if you called count multiple times, it
would return the same number without re-running the query, and you could
share the query work between N calls to count and one call to
fetch/forEach/map (but only one call! future calls would return
nothing!) While there's a minor performance hit from getting rid of
this cache, it should also use a little less memory, and enable use
cases like
{{#with someCursor}}
{{#if count}}
{{#each this}}
...
{{/each}}
{{/if}}
{{/with}}
which didn't work before because even the deps invalidation didn't
rewind the cursor.
Also, as a minor optimization, skip an EJSON.clone if there's a
projection, because projection functions are guaranteed to clone.
Fixes #2114