Re: Add json_typeof() and json_is_*() functions.

On Mon, Jul 29, 2013 at 5:36 PM, Merlin Moncure <mmoncure(at)gmail(dot)com> wrote:
> On Mon, Jul 29, 2013 at 2:16 AM, Andrew Tipton <andrew(at)kiwidrew(dot)com> wrote:
>> The attached patch adds four new SQL functions for the JSON type:
>> json_typeof(json) RETURNS text
>> json_is_object(json) RETURNS boolean
>> json_is_array(json) RETURNS boolean
>> json_is_scalar(json) RETURNS boolean
>>
>> The motivating use-case for this patch is the ability to easily create a
>> domain type for what RFC 4627 calls "json text", where the top-level value
>> must be either an object or array. An example of this usage is:
>>
>> CREATE DOMAIN json_document AS json CHECK (NOT json_is_scalar(VALUE));
>>
>> An additional use-case arises when writing functions which can handle
>> arbitrary JSON values. This can be difficult when nested objects or arrays
>> are present or when the input may be either an array or an object. Many of
>> the built-in functions will raise an error when presented with an "invalid"
>> value, such as when giving an array to json_object_keys(). The
>> json_typeof() and json_is_*() functions should make it easier to call the
>> correct function in these cases, e.g.:
>>
>> CASE json_typeof($1)
>> WHEN 'object' THEN json_object_keys($1)
>> WHEN 'array' THEN json_array_elements($1)
>> ELSE $1
>> END
>>
>> These new functions operate by making a single call to json_lex() to get the
>> first token of the JSON value; this token uniquely determines the value's
>> type. (Thanks to Merlin Moncure for suggesting this approach.)
>>
>> The patch also updates the "JSON Functions and Operators" section of the
>> docs to ensure that the words "value", "object", and "array" are used in a
>> consistent manner. "JSON object" and "JSON array" refer to parameters which
>> must be an object or an array or to results which are always an object or an
>> array. "JSON value" refers to parameters or results which may be any kind
>> of JSON.
>
> you're welcome! :-).
>
> small point:
> Personally I would prune the supplied functions to json_typeof() and
> json_is_scalar(). These functions are in the public namespace so
> there is a certain minimum bang/buck ratio which IMNSHO
> json_is_object() and json_is_array() don't meet -- just call
> json_typeof() to get that info.

+1, but I'm wondering why we need anything more than just
json_typeof(). Doesn't that pretty much cover it?

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
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