Thank you very much. Will try.
On Friday, April 7, 2017 at 3:09:28 AM UTC+8, Jens Alfke wrote:
>
>
> On Apr 4, 2017, at 9:27 PM, dyowee <csharpen...@gmail.com <javascript:>>
> wrote:
>
> Like what is done in CouchDB to return all documents of the same type
> "all": {
>
> <https://wiki.apache.org/couchdb/HTTP_view_API#CA-d9441d2b8848184b52055fd6f98fb96d93dcbb46_8>
> "map": "function(doc) { if (doc.type == 'customer') emit(null, doc) }"
> }
>
>
> That key is a JavaScript `null` object, which is equivalent to a JSON
> `null`. In Objective-C you would express that as an NSNull object, i.e.
> `[NSNull null]`.
> JavaScript is weird: its `null` is a real value. It's *not* the same
> thing as an Objective-C `nil` (or a Java or C# `null`, or a C `NULL`) —
> those are all equivalent to JavaScript’s `undefined`.
>
> In this map function the `null` is just being used as a placeholder
> because the developer doesn’t care what order the values should be in, so
> it gives them all the same key. It actually doesn’t matter what key you use
> here; you could put `0` or an empty string, or even 12345 or “foobar”.
>
> If you find yourself creating multiple views like this but with different
> document type strings, a better way to do it is to emit doc.type as the
> key, and emit it for all docs that have a `type` property. This gives you a
> single view that can be used to find docs of all types, not just ‘customer’.
>
> —Jens
>
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