Re: 9.3 Json & Array's - Mailing list pgsql-hackers

 

> On 24 September 2013 at 13:46 Andrew Dunstan <andrew@dunslane.net> wrote:

> 
> 
> Feel free to ask questions.
> 
> The heart of the API is the event handlers defined in this stuct in 
> include/utils/jsonapi.h:
> 
>     typedef struct JsonSemAction
>     {
>          void       *semstate;
>          json_struct_action object_start;
>          json_struct_action object_end;
>          json_struct_action array_start;
>          json_struct_action array_end;
>          json_ofield_action object_field_start;
>          json_ofield_action object_field_end;
>          json_aelem_action array_element_start;
>          json_aelem_action array_element_end;
>          json_scalar_action scalar;
>     } JsonSemAction;
> 
> 
> Basically there is a handler for the start and end of each non-scalar 
> structural element in JSON, plus a handler for scalars.
> 
> There are several problems that will be posed by processing nested 
> arrays and objects, including:
> 
>   * in effect you would need to construct a stack of state that could be
>     pushed and popped

 

True.

>   * JSON arrays aren't a very good match for SQL arrays - they are
>     unidimensional and heterogenous.

 

This is true, but I think one would have to start with an assumption that the data is valid for an SQL type and then check again once one gets it done.    JSON is a pretty flexible format which makes it a poor match in many cases for SQL types generally.  But I think the example so far (with json_populate_recordset) is a good one, namely a best effort conversion.

> 
> 
> I'm not saying this can't be done - it will just take a bit of effort.

 

Yeah, looking through the code, I think it will be more work than I originally thought but that just means it will take longer.
> 
> cheers
> 
> andrew
> 
> 
> 
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Best Wishes,
Chris Travers
http://www.2ndquadrant.com
PostgreSQL Services, Training, and Support