CODEWITHSUNDEEP
sqljsonpostgresqlimportcommon-table-expression
Picl
Picl

Reputation: 149

Populate multiple tables from a single JSON object with json_populate_recordset

I've read related question, but unlike user kenthewala, I want to get an array of JSON objects into the database.

My JSON file looks like this:

{
"tablename_a":[{"a_id":1,"b_id":2,"c_id":3},
 {"a_id":2,"b_id":51,"c_id":3}],
"tablename_b":[{"b_id":2,"name":"John Doe", "z_id":123},
 {"b_id":51,"name":"Mary Ann", "z_id":412}],
"tablename_c":[{"c_id":3, "OS type":"Windows 7"}],
"tablename_z":[{"z_id":123, "Whatever":"Something"},
{"z_id":123, "Whatever":"Something else"}]
}

Tables with the according names already exist in the db.

In pseudo-code I imagined something like

for each key in JSON_FILE as tbl_name
(
  insert into tbl_name select * from json_populate_recordset
  (
    null::tbl_name, 'content of tbl_name'
  )
)

But I'm not sure, how to realize this.

I'm using PostgreSQL 9.3.5 (and PHP 5.3.3 if that helps).

The table structure resembles the JSON file (as I exported the JSON originally from the db):

create table tablename_a (a_id integer, b_id integer, c_id integer);
create table tablename_b (b_id integer, name text, z_id integer);

and so on.

Upvotes: 5

Views: 5399

Answers (1)

Erwin Brandstetter
Erwin Brandstetter

Reputation: 657092

3 Steps:

  1. Access field of JSON object wich ->.
  2. Create a derived table from the JSON array of records using json_populate_recordset().
  3. Decompose the row-type for the INSERT command.

To reuse the input value for all tables, wrap it in data-modifying CTEs:

WITH input AS (
   SELECT '{
      "tablename_a":[{"a_id":1,"b_id":2,"c_id":3},
       {"a_id":2,"b_id":51,"c_id":3}],
      "tablename_b":[{"b_id":2,"name":"John Doe", "z_id":123},
       {"b_id":51,"name":"Mary Ann", "z_id":412}],
      "tablename_c":[{"c_id":3, "OS type":"Windows 7"}],
      "tablename_z":[{"z_id":123, "Whatever":"Something"},
      {"z_id":123, "Whatever":"Something else"}]
      }'::json AS j
   )
,  a AS (
   INSERT INTO tablename_a
   SELECT t.*
   FROM   input i
        , json_populate_recordset(NULL::tablename_a, i.j->'tablename_a') t
   )
,  b AS (
   INSERT INTO tablename_b
   SELECT t.*
   FROM   input i
        , json_populate_recordset(NULL::tablename_b, i.j->'tablename_b') t
   )
   -- ... more ...
INSERT INTO tablename_z
SELECT t.*
FROM   input i
     , json_populate_recordset(NULL::tablename_z, i.j->'tablename_z') t
;

SQL Fiddle.

Using implicit JOIN LATERAL. Related:

Upvotes: 6

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