| Bug #79643 | Empty strings as keys probably not handled correctly by json_extract() | ||
|---|---|---|---|
| Submitted: | 14 Dec 2015 22:48 | Modified: | 20 Jan 2016 12:30 |
| Reporter: | Pawel Mroszczyk | Email Updates: | |
| Status: | Closed | Impact on me: | |
| Category: | MySQL Server: JSON | Severity: | S3 (Non-critical) |
| Version: | OS: | Any | |
| Assigned to: | CPU Architecture: | Any | |
[21 Dec 2015 11:12]
Knut Anders Hatlen
Hi Pawel,
I believe the unquoted variants ('$.', '$.....', etc) should cause an error to be raised. According to https://dev.mysql.com/doc/refman/5.7/en/json-path-syntax.html, unquoted key names in JSON paths must be ECMAScript identifiers. An empty string cannot be an identifier, if I read the ECMAScript specification correctly.
I don't see any reason to reject the quoted variants, though. Since JSON objects can be created with empty key names, it should be possible to construct paths with empty key names.
[20 Jan 2016 12:30]
Jon Stephens
Documented fix in the MySQL 5.8.0 changelog, as follows:
The empty string is now accepted as a key when used as such with
JSON functions. In this case, it must be quoted.
Closed.
Description: I think there may be a bug with path expressions used in json_extract(). I can create a JSON object with an empty key (and try to extract something else) - no error: mysql> select json_extract( '{"":42}', '$.bla'); +-----------------------------------+ | json_extract( '{"":42}', '$.bla') | +-----------------------------------+ | NULL | +-----------------------------------+ 1 row in set (0.00 sec) But how would I go about extracting value from that empty key? mysql> select json_extract( '{"":42}', '$.'); ERROR 3143 (42000): Invalid JSON path expression. The error is around character position 2 in '$.'. mysql> select json_extract( '{"":42}', '$.""'); ERROR 3143 (42000): Invalid JSON path expression. The error is around character position 4 in '$.""'. I'm not an expert on JSON, but my best guess is that empty strings are valid keys. How to repeat: Shown in the description Suggested fix: Again, I'm not an expert on the matter. I'm implementing json_extract()-like functionality in mysqls and I ran into the same dilemma. Right now I'm implementing it so that both of these expressions will extract the empty key: $. $."" This opens discussion regarding further "weird but valid" JSON paths. If above is valid, then so should these be: $.....foo.....bar $...."" $.foo."".bar Implementation-wise, so far supporting the empty string seems simple, while checking and guarding against it being empty results in many corner-case if statements. So my personal preference is to support empty keys.