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Filling array gaps during jsonb subscripting

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This commit introduces two new flags for jsonb assignment:

* JB_PATH_FILL_GAPS: Appending array elements on the specified position, gaps
  are filled with nulls (similar to the JavaScript behavior).  This mode also
  instructs to   create the whole path in a jsonb object if some part of the
  path (more than just the last element) is not present.

* JB_PATH_CONSISTENT_POSITION: Assigning keeps array positions consistent by
  preventing prepending of elements.

Both flags are used only in jsonb subscripting assignment.

Initially proposed by Nikita Glukhov based on polymorphic subscripting
patch, but transformed into an independent change.

Discussion: https://postgr.es/m/CA%2Bq6zcV8qvGcDXurwwgUbwACV86Th7G80pnubg42e-p9gsSf%3Dg%40mail.gmail.com
Discussion: https://postgr.es/m/CA%2Bq6zcX3mdxGCgdThzuySwH-ApyHHM-G4oB1R0fn0j2hZqqkLQ%40mail.gmail.com
Discussion: https://postgr.es/m/CA%2Bq6zcVDuGBv%3DM0FqBYX8DPebS3F_0KQ6OVFobGJPM507_SZ_w%40mail.gmail.com
Discussion: https://postgr.es/m/CA%2Bq6zcVovR%2BXY4mfk-7oNk-rF91gH0PebnNfuUjuuDsyHjOcVA%40mail.gmail.com
Author: Dmitry Dolgov
Reviewed-by: Tom Lane, Arthur Zakirov, Pavel Stehule, Dian M Fay
Reviewed-by: Andrew Dunstan, Chapman Flack, Merlin Moncure, Peter Geoghegan
Reviewed-by: Alvaro Herrera, Jim Nasby, Josh Berkus, Victor Wagner
Reviewed-by: Aleksander Alekseev, Robert Haas, Oleg Bartunov
This commit is contained in:
Alexander Korotkov
2021-01-31 23:51:01 +03:00
parent 676887a3b0
commit 81fcc72e66
4 changed files with 452 additions and 15 deletions
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24
doc/src/sgml/json.sgml
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@ -648,6 +648,30 @@ UPDATE table_name SET jsonb_field['a'] = '1';
-- Where jsonb_field was NULL, it is now [1]
UPDATE table_name SET jsonb_field[0] = '1';
</programlisting>
If an index is specified for an array containing too few elements,
<literal>NULL</literal> elements will be appended until the index is reachable
and the value can be set.
<programlisting>
-- Where jsonb_field was [], it is now [null, null, 2];
-- where jsonb_field was [0], it is now [0, null, 2]
UPDATE table_name SET jsonb_field[2] = '2';
</programlisting>
A <type>jsonb</type> value will accept assignments to nonexistent subscript
paths as long as the last existing path key is an object or an array. Since
the final subscript is not traversed, it may be an object key. Nested arrays
will be created and <literal>NULL</literal>-padded according to the path until
the value can be placed appropriately.
<programlisting>
-- Where jsonb_field was {}, it is now {'a': [{'b': 1}]}
UPDATE table_name SET jsonb_field['a'][0]['b'] = '1';
-- Where jsonb_field was [], it is now [{'a': 1}]
UPDATE table_name SET jsonb_field[0]['a'] = '1';
</programlisting>
</para>