1
0
mirror of https://github.com/postgres/postgres.git synced 2025-07-27 12:41:57 +03:00

Implementation of subscripting for jsonb

Subscripting for jsonb does not support slices, does not have a limit for the
number of subscripts, and an assignment expects a replace value to have jsonb
type.  There is also one functional difference between assignment via
subscripting and assignment via jsonb_set().  When an original jsonb container
is NULL, the subscripting replaces it with an empty jsonb and proceeds with
an assignment.

For the sake of code reuse, we rearrange some parts of jsonb functionality
to allow the usage of the same functions for jsonb_set and assign subscripting
operation.

The original idea belongs to Oleg Bartunov.

Catversion is bumped.

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 23:50:40 +03:00
parent dc43492e46
commit 676887a3b0
12 changed files with 988 additions and 108 deletions

View File

@ -602,6 +602,57 @@ SELECT jdoc->'guid', jdoc->'name' FROM api WHERE jdoc @> '{"tags": ["qu
</para>
</sect2>
<sect2 id="jsonb-subscripting">
<title><type>jsonb</type> Subscripting</title>
<para>
The <type>jsonb</type> data type supports array-style subscripting expressions
to extract and modify elements. Nested values can be indicated by chaining
subscripting expressions, following the same rules as the <literal>path</literal>
argument in the <literal>jsonb_set</literal> function. If a <type>jsonb</type>
value is an array, numeric subscripts start at zero, and negative integers count
backwards from the last element of the array. Slice expressions are not supported.
The result of a subscripting expression is always of the jsonb data type.
</para>
<para>
An example of subscripting syntax:
<programlisting>
-- Extract object value by key
SELECT ('{"a": 1}'::jsonb)['a'];
-- Extract nested object value by key path
SELECT ('{"a": {"b": {"c": 1}}}'::jsonb)['a']['b']['c'];
-- Extract array element by index
SELECT ('[1, "2", null]'::jsonb)[1];
-- Update object value by key. Note the quotes around '1': the assigned
-- value must be of the jsonb type as well
UPDATE table_name SET jsonb_field['key'] = '1';
-- Filter records using a WHERE clause with subscripting. Since the result of
-- subscripting is jsonb, the value we compare it against must also be jsonb.
-- The double quotes make "value" also a valid jsonb string.
SELECT * FROM table_name WHERE jsonb_field['key'] = '"value"';
</programlisting>
<type>jsonb</type> assignment via subscripting handles a few edge cases
differently from <literal>jsonb_set</literal>. When a source <type>jsonb</type>
is <literal>NULL</literal>, assignment via subscripting will proceed as if
it was an empty JSON object:
<programlisting>
-- Where jsonb_field was NULL, it is now {"a": 1}
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>
</para>
</sect2>
<sect2>
<title>Transforms</title>