json functions: double quotes added when going through a variable

Question

Im stuck with what it seems simple question, when I create a JSON using the MariaDB/MySQL json functions going through variables, it adds double quotes which is annoying. However, if I don't go through variables, it works fine. Unfortunately I have to go through variables as I'm building my JSON using a recursive function:

1. without variables:

   declare temp_json JSON;
   set temp_json = json_object('data',json_object("jsonapi",json_object("version", "1.0")));
   select temp_json
   

   OUTPUT

   {"data": {"jsonapi": {"version": "1.0"}}}
   

2. with variables

   declare temp_json JSON;
   declare jsonapiheader JSON;
   set jsonapiheader = json_object("jsonapi",json_object("version", "1.0"));
   set temp_json = json_object('data',jsonapiheader);
   select temp_json
   

   OUTPUT

   {"data": "{\"jsonapi\": {\"version\": \"1.0\"}}"}` 
   

So how do I do like 2) but with the output of 1) ?

my system: MariaDB 10.2.9

Answer 1

First, generally speaking, there are two types of JSON,

1. JSON-validated text.
2. Binary JSON (Mongo calls it BSON, PostgreSQL calls it JSONB, also Apache Avro).

For reference MariaDB has neither of these. It has a JSON type, but that type is nothing more than un-validated text, from the docs

JSON is an alias for LONGTEXT introduced for compatibility reasons with MySQL's JSON data type. MariaDB implements this as a LONGTEXT rather, as the JSON data type contradicts the SQL standard, and MariaDB's benchmarks indicate that performance is at least equivalent.

If you need a validated column, you need to use a CHECK constraint. So essentially, internally all the functions that "do JSON", essentially read text process it internally and output text.

So the problem you're running into is that json_object doesn't know that the value is JSON-text. There isn't an easy around that. The only option from a MariaDB's perspective is to implement each function as accepting a value, and another one as accepting a jdoc, or doing it right and implementing a real type for JSON.

As a side note, there is one function that does accept two jdocs, one to operate on, and one as an argument. That function is JSON_MERGE.

See also,

• Does MariaDB support native JSON column data type?

I would highly suggest migrating to PostgreSQL if it's not too late. Not just do you get a binary JSON type but you get a rich library of functions, and operators, and indexes for that type.

Answer 2

@Evan Carroll is certainly right about the general implementation of JSON in MariaDB. But if you are still going with MariaDB this might help you:

The behavior you describe is a serious bug which is tracked here: https://jira.mariadb.org/browse/MDEV-13701 As far as I understood its expected to be fixed with MariaDB-10.2.12.

For the time being I use the following hack:

set @jsonapiheader = json_object("jsonapi",json_object("version", CAST(1.0 AS DECIMAL(2,1))));
set @temp_json = concat('{"data":',@jsonapiheader,'}');
select @temp_json, json_valid(@temp_json);

Output:

{"data":{"jsonapi": {"version": 1.0}}}        |       1

Also look at the CAST within the first JSON_OBJECT. It also works with variables and functions and results in a more accurate JSON output.