Context lenses to set/get values in json values.

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&gt;,isActive)&#39;, '...
nested json value ...')

may return
uID | email | name | isActive
--------------------------------------------------------------------------
"u1" | "admin@pmsoft.eu <mailto:admin@pmsoft.eu>" | "administrator"
| true
"u2" | "normal@pmsoft.eu <mailto:normal@pmsoft.eu>" | "user"
| true
"u3" | "testUser@pmsoft.eu <mailto:testUser@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&gt;,isActive)&#39;);
query_to_json( 'select * from Person where ... ',
'app.users.{:uID}.(email,data.name <http://data.name&gt;,isActive)&#39;);

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&gt;)&#39;, 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

--
Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackers

On Wed, Oct 8, 2014 at 4:25 PM, Andrew Dunstan <andrew@dunslane.net> wrote:

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&gt;,isActive)&#39;, '...
nested json value ...')

may return
uID | email | name | isActive
------------------------------------------------------------
--------------
"u1" | "admin@pmsoft.eu <mailto:admin@pmsoft.eu>" | "administrator" |
true
"u2" | "normal@pmsoft.eu <mailto:normal@pmsoft.eu>" | "user"
| true
"u3" | "testUser@pmsoft.eu <mailto:testUser@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&gt;,isActive)&#39;);
query_to_json( 'select * from Person where ... ',
'app.users.{:uID}.(email,data.name <http://data.name&gt;,isActive)&#39;);

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&gt;)&#39;, 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

Hello.

My personal interest is to send updates to a single json value in the
server. Which is the best way to make a update to a json value in postgres
without a full update of the already stored value?? the -> operator
extract a internal value, but to update the value I don't see any operator.

I was not familiar with the extensions, but it looks like the best way to
start is to create a extension with possible implementations of new
functions. I will do so.

In my project I considered to use mongo, but in my case the core part of
the model match perfectly a relational schema. I have some leaf concepts
that will change frequently, and to avoid migrations I store that
information in a json value. To make changes in such leaf values I would
like to have a "context lenses like api" in the server. I will start with
some toy extension and try to feel if this make sense.

Regards.
Pawel.

On 10/08/2014 12:13 PM, Paweł Cesar Sanjuan Szklarz wrote:

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?

Hello.

My personal interest is to send updates to a single json value in the
server. Which is the best way to make a update to a json value in
postgres without a full update of the already stored value?? the ->
operator extract a internal value, but to update the value I don't see
any operator.

I was not familiar with the extensions, but it looks like the best way
to start is to create a extension with possible implementations of new
functions. I will do so.

In my project I considered to use mongo, but in my case the core part
of the model match perfectly a relational schema. I have some leaf
concepts that will change frequently, and to avoid migrations I store
that information in a json value. To make changes in such leaf values
I would like to have a "context lenses like api" in the server. I will
start with some toy extension and try to feel if this make sense.

There is work already being done on providing update operations.

cheers

andrew

--
Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackers

On 8 October 2014 18:39, Andrew Dunstan <andrew@dunslane.net> wrote:

On 10/08/2014 12:13 PM, Paweł Cesar Sanjuan Szklarz wrote:

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?

Hello.

My personal interest is to send updates to a single json value in the
server. Which is the best way to make a update to a json value in postgres
without a full update of the already stored value?? the -> operator extract
a internal value, but to update the value I don't see any operator.

I was not familiar with the extensions, but it looks like the best way to
start is to create a extension with possible implementations of new
functions. I will do so.

In my project I considered to use mongo, but in my case the core part of
the model match perfectly a relational schema. I have some leaf concepts
that will change frequently, and to avoid migrations I store that
information in a json value. To make changes in such leaf values I would
like to have a "context lenses like api" in the server. I will start with
some toy extension and try to feel if this make sense.

There is work already being done on providing update operations.

I've been looking out for that. Has there been a discussion on how
that would look yet that you could point me to?

--
Thom

--
Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackers

On 10/08/2014 02:04 PM, Thom Brown wrote:

There is work already being done on providing update operations.

I've been looking out for that. Has there been a discussion on how
that would look yet that you could point me to?

https://github.com/erthalion/jsonbx

Note that a) it's an extension, and b) it's jsonb only.

cheers

andrew

--
Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackers

On 8 October 2014 at 20:39, Andrew Dunstan <andrew@dunslane.net> wrote:

On 10/08/2014 02:04 PM, Thom Brown wrote:

There is work already being done on providing update operations.

I've been looking out for that. Has there been a discussion on how
that would look yet that you could point me to?

https://github.com/erthalion/jsonbx

Note that a) it's an extension, and b) it's jsonb only.

Is the intention to get these in-core, or to remain in an extension? These
appear to be candidates as first class citizens.

Thom