Subject: [PATCH v45 3/3] Replace assuming a composite object on a scalar

From: Dmitrii Dolgov <[email-masked]>
Date: Thu, 7 Jan 2021 09:04:39 +0100

For jsonb subscripting assignment it could happen that the provided path
assumes an object or an array at some level, but the source jsonb has a
scalar value there. Originally the update operation will be skipped and
no message will be shown that nothing happened. Return an error to
indicate such situations.
---
 doc/src/sgml/json.sgml              | 22 ++++++++++++++++++++--
 src/backend/utils/adt/jsonfuncs.c   | 11 +++++++++++
 src/test/regress/expected/jsonb.out | 12 ++++++++++++
 src/test/regress/sql/jsonb.sql      |  8 ++++++++
 4 files changed, 51 insertions(+), 2 deletions(-)

diff --git a/doc/src/sgml/json.sgml b/doc/src/sgml/json.sgml
index 9af015d222..924762e128 100644
--- a/doc/src/sgml/json.sgml
+++ b/doc/src/sgml/json.sgml
@@ -612,8 +612,23 @@ SELECT jdoc-&gt;'guid', jdoc-&gt;'name' FROM api WHERE jdoc @&gt; '{"tags": ["qu
    <literal>path</literal> argument in <literal>jsonb_set</literal> function,
    e.g. in case of arrays it is a 0-based operation or that negative integers
    that appear in <literal>path</literal> count from the end of JSON arrays.
-   The result of subscripting expressions is always jsonb data type. An
-   example of subscripting syntax:
+   The result of subscripting expressions is always jsonb data type.
+
+  <para>
+   <command>UPDATE</command> statements may use subscripting in the
+   <literal>SET</literal> clause to modify <type>jsonb</type> values. Every
+   affected value must conform to the path defined by the subscript(s). If the
+   path contradicts structure of modified <type>jsonb</type> for any individual
+   value (e.g. path <literal>val['a']['b']['c']</literal> assumes keys
+   <literal>'a'</literal> and <literal>'b'</literal> have object values
+   assigned to them, but if <literal>val['a']</literal> or
+   <literal>val['b']</literal> is null, a string, or a number, then the path
+   contradicts with the existing structure), an error is raised even if other
+   values do conform.
+  </para>
+  <para>
+
+   An example of subscripting syntax:
 <programlisting>
 -- Extract value by key
 SELECT ('{"a": 1}'::jsonb)['a'];
@@ -628,6 +643,9 @@ SELECT ('[1, "2", null]'::jsonb)[1];
 -- needs to be of jsonb type as well
 UPDATE table_name SET jsonb_field['key'] = '1';
 
+-- This will raise an error if jsonb_field is {"a": 1}
+UPDATE table_name SET jsonb_field['a']['b']['c'] = '1';
+
 -- Select records using where clause with subscripting. Since the result of
 -- subscripting is jsonb and we basically want to compare two jsonb objects, we
 -- need to put the value in double quotes to be able to convert it to jsonb.
diff --git a/src/backend/utils/adt/jsonfuncs.c b/src/backend/utils/adt/jsonfuncs.c
index f14f6c3191..ebc0b06f5b 100644
--- a/src/backend/utils/adt/jsonfuncs.c
+++ b/src/backend/utils/adt/jsonfuncs.c
@@ -4943,6 +4943,17 @@ setPath(JsonbIterator **it, Datum *path_elems,
 			break;
 		case WJB_ELEM:
 		case WJB_VALUE:
+			/*
+			 * If instructed complain about attempts to replace whithin a
+			 * scalar value.
+			 */
+			if ((op_type & JB_PATH_FILL_GAPS) && (level < path_len - 1))
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+						 errmsg("cannot replace existing key"),
+						 errdetail("The path assumes key is a composite object, "
+								   "but it is a scalar value.")));
+
 			res = pushJsonbValue(st, r, &v);
 			break;
 		default:
diff --git a/src/test/regress/expected/jsonb.out b/src/test/regress/expected/jsonb.out
index b7c268b53f..0df808c36d 100644
--- a/src/test/regress/expected/jsonb.out
+++ b/src/test/regress/expected/jsonb.out
@@ -5134,6 +5134,18 @@ select * from test_jsonb_subscript;
   1 | {"a": [null, {"c": [null, null, 1]}]}
 (1 row)
 
+-- trying replace assuming a composite object, but it's a scalar
+delete from test_jsonb_subscript;
+insert into test_jsonb_subscript values (1, '{"a": 1}');
+update test_jsonb_subscript set test_json['a']['b']['c'] = '1';
+ERROR:  cannot replace existing key
+DETAIL:  The path assumes key is a composite object, but it is a scalar value.
+update test_jsonb_subscript set test_json['a'][0]['c'] = '1';
+ERROR:  cannot replace existing key
+DETAIL:  The path assumes key is a composite object, but it is a scalar value.
+update test_jsonb_subscript set test_json['a'][0][0] = '1';
+ERROR:  cannot replace existing key
+DETAIL:  The path assumes key is a composite object, but it is a scalar value.
 -- jsonb to tsvector
 select to_tsvector('{"a": "aaa bbb ddd ccc", "b": ["eee fff ggg"], "c": {"d": "hhh iii"}}'::jsonb);
                                 to_tsvector                                
diff --git a/src/test/regress/sql/jsonb.sql b/src/test/regress/sql/jsonb.sql
index 0320db0ea4..c62a2f9aec 100644
--- a/src/test/regress/sql/jsonb.sql
+++ b/src/test/regress/sql/jsonb.sql
@@ -1371,6 +1371,14 @@ insert into test_jsonb_subscript values (1, '{"a": []}');
 update test_jsonb_subscript set test_json['a'][1]['c'][2] = '1';
 select * from test_jsonb_subscript;
 
+-- trying replace assuming a composite object, but it's a scalar
+
+delete from test_jsonb_subscript;
+insert into test_jsonb_subscript values (1, '{"a": 1}');
+update test_jsonb_subscript set test_json['a']['b']['c'] = '1';
+update test_jsonb_subscript set test_json['a'][0]['c'] = '1';
+update test_jsonb_subscript set test_json['a'][0][0] = '1';
+
 -- jsonb to tsvector
 select to_tsvector('{"a": "aaa bbb ddd ccc", "b": ["eee fff ggg"], "c": {"d": "hhh iii"}}'::jsonb);
 
-- 
2.21.0

--2v7pubbjx3p2om6u--