On Mar 8, 2013, at 1:21 PM, Andrew Dunstan <[email protected]> wrote:
> Here's what rfc2119 says about that wording:
>
> 4. SHOULD NOT This phrase, or the phrase "NOT RECOMMENDED" mean that
> there may exist valid reasons in particular circumstances when the
> particular behavior is acceptable or even useful, but the full
> implications should be understood and the case carefully weighed
> before implementing any behavior described with this label.
I suspect this was allowed for the JavaScript behavior where multiple keys are
allowed, but the last key in the list wins.
> So we're allowed to do as Robert chose, and I think there are good reasons
> for doing so (apart from anything else, checking it would slow down the
> parser enormously).
Yes, but the implications are going to start biting us on the ass now.
> Now you could argue that in that case the extractor functions should allow it
> too, and it's probably fairly easy to change them to allow it. In that case
> we need to decide who wins. We could treat a later field lexically as
> overriding an earlier field of the same name, which I think is what David
> expected. That's what plv8 does (i.e. it's how v8 interprets JSON):
>
> andrew=# create or replace function jget(t json, fld text) returns
> text language plv8 as ' return t[fld]; ';
> CREATE FUNCTION
> andrew=# select jget('{"f1":"x","f1":"y"}','f1');
> jget
> ------
> y
> (1 row)
>
>
> Or you could take the view I originally took that in view of the RFC wording
> we should raise an error if this was found.
>
> I can live with either view.
I’m on the fence. On the one hand, I like the plv8 behavior, which is nice for
a dynamic language. On the other hand, I don't much care for it in my database,
where I want data storage requirements to be quite strict. I hate the idea of
"0000-00-00" being allowed as a date, and am uncomfortable with allowing
duplicate keys to be stored in the JSON data type.
So my order of preference for the options would be:
1. Have the JSON type collapse objects so the last instance of a key wins and
is actually stored
2. Throw an error when a JSON type has duplicate keys
3. Have the accessors find the last instance of a key and return that value
4. Let things remain as they are now
On second though, I don't like 4 at all. It means that the JSON type things a
value is valid while the accessor does not. They contradict one another.
Best,
David
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