On 10/08/2014 04:38 AM, Paweł Cesar Sanjuan Szklarz wrote:
Hello.
I am interested in the json type on postgresql. I would like to
implement additional operations on the json structure that may
extract/insert table like information from the json tree structure.
I have a implementation on javascript that shows this type of
operations. You can see examples in this page
https://github.com/paweld2/eelnss/wiki
Following the examples in the previous page, it may by possible to
implement a function similar to json_populate_record to extract
multiple records from a single json value, for example:
select * from json_populate_records_with_clen(null::myrowtype_users,
'app.users.{:uID}.(email,data.name <http://data.name>,isActive)', '...
nested json value ...')
may return
uID | email | name | isActive
--------------------------------------------------------------------------
"u1" | "ad...@pmsoft.eu <mailto:ad...@pmsoft.eu>" | "administrator"
| true
"u2" | "nor...@pmsoft.eu <mailto:nor...@pmsoft.eu>" | "user"
| true
"u3" | "testu...@pmsoft.eu <mailto:testu...@pmsoft.eu>" | "testUser"
| false
Also, assuming that we have a table User as above (uID, email, name,
isActive), with context lenses it is very simple to map the table to a
json object. I assume that a similar api to table_to_xml,query_to_xml
may be provided:
table_to_json( Person, 'app.users.{:uID}.(email,data.name
<http://data.name>,isActive)');
query_to_json( 'select * from Person where ... ',
'app.users.{:uID}.(email,data.name <http://data.name>,isActive)');
I don't know the details about the integration of functions/operators
to sql queries, but because context lenses maps between tables and
tree objects, it may be possible to use a column json value as a
separate table in the queries. Assume the table
create table Person {
pID Integer
address Json
}
then it may be possible to query:
select * from Person as P left join ( select * from
json_populate_records_with_clen(null::addressType,
'addres.(street.number, street.local,city.code,city.name
<http://city.name>)', P.address);
A final api for such functions needs to be defined. If such functions
may be usefull, I can try to prepare a implementation in postgres base
code.
I don't think we need to import Mongo type notation here. But there is
probably a good case for some functions like:
json_table_agg(anyrecord) -> json
which would work like json_agg() but would return an array of arrays
instead of an array of objects. The caller would be assumed to know
which field is which in the array. That should take care of both the
table_to_json and query_to_json suggestions above.
In the other direction, we could have something like:
json_populate_recordset_from_table(base anyrecord, fields text[],
jsontable json) -> setof record
where jsontable is an array of arrays of values and fields is a
corresponding array of field names.
I'm not sure how mainstream any of this is. Maybe an extension would be
more appropriate?
cheers
andrew
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