1

I've been laboring away trying to create a procedure which can data JSONB (or JSON, doesn't really matter), a table, and convert the JSON to a record and insert that record into the table. This is (roughly) the closest I've come to getting a functional prototype:

CREATE OR REPLACE FUNCTION fn_alter_entity(data JSONB, table_type anyelement) RETURNS VOID
    SECURITY INVOKER
    LANGUAGE plpgsql
AS $$
    DECLARE
        record RECORD;
        record_type RECORD;
    BEGIN
        EXECUTE format('SELECT x.* FROM (SELECT a.* FROM CAST(NULL as %s) a) x', pg_typeof(table_type))
            INTO record_type;
        record := jsonb_populate_record(record_type, data);
        INSERT INTO users SELECT (record).* RETURNING id;
    END;
$$;

So let's say that I do the following:

SELECT fn_alter_entity('{"a": "b"}'::JSONB, users);

I receive the following error:

ERROR: record type has not been registered
SQL state: 42809
Context: SQL statement "INSERT INTO users SELECT (record).* RETURNING id"
PL/pgSQL function fn_alter_entity(jsonb,anyelement) line 9 at SQL statement

Now, obviously the reason I'm receiving that error is that record_type is not actually a real record type. Now, normally we would just do something like jsonb_populate_record(data, NULL::users) or jsonb_populate_record(data, NULL::events) or the like. But what if I want that record type to be dynamic? Is there any possibility? I feel like I'm on the verge of nailing this down, but just can't quite get over the hump. All I want to do is be able to transform JSON into a record.

  • could you provide examples of what you're trying to do with input and output rather than your psuedo code that doesn't work? – Evan Carroll Jun 27 '17 at 1:26
  • "record type to be dynamic" - how? I think you may be expecting more flexibility from postgres's type system than it can provide. – Craig Ringer Jun 27 '17 at 1:35
  • @EvanCarroll, my examples, with input and output, don't work either. What I provided is not pseudocode, but rather a fully valid and compiling function. I have amended my question to provide further detail, but the original problem remains, detail or not. – ironhardchaw Jun 27 '17 at 2:35
  • @CraigRinger I have amended my question to hopefully clarify a bit. If it's not possible then so be it. I was just hoping to avoid having to write multiple copies of the same procedure if I could help it! What better than to be able to re-use code right? – ironhardchaw Jun 27 '17 at 2:36
0

I think you want something like this.

CREATE OR REPLACE FUNCTION fn_alter_entity(data JSONB, t TEXT )
  RETURNS VOID
  SECURITY INVOKER
AS $$
    BEGIN
        EXECUTE FORMAT(
          'INSERT INTO %I SELECT * FROM jsonb_populate_record( null::%I, $1);',
          t,
          t
        )
        USING data;
    END;
$$
LANGUAGE plpgsql
VOLATILE;

CREATE TABLE foo ( a int );
CREATE TABLE bar ( a int, b text );

SELECT fn_alter_entity( '{"a": 5}', 'foo' );
SELECT fn_alter_entity( '{"a": 42}', 'foo' );
SELECT fn_alter_entity( '{"a": 5, "b": "foo"}', 'bar' );
SELECT fn_alter_entity( '{"a": 42, "b": "baz"}', 'bar' );

test=# TABLE foo;
 a  
----
  5
 42
(2 rows)

test=# TABLE bar;
 a  |  b  
----+-----
  5 | foo
 42 | baz
(2 rows)

But seeing where you may be going, I would highly suggest you look into PostgREST.

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