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Recursive JSON generation in PostgreSQL

I have the following tables on a PostgreSQL 9.5 server: tables

A remarkable structural thing is that it is locationtheoretically infinitely recursive. I need to create a JSON message from the root location, recursive to all subitems; each locationhas some properties, an array of elements inventoryand an array of a child locations.

How to create a request for execution for this? I review the various PostgreSQL JSON functions, the LATERAL keyword, CTE, and get a little confused. I made JSON output with non-recursive requests, but am not sure how to handle recursion properly.

Here is an example output:

{
  "id": 1000,
  "name": "By Location",
  "type": "SITE",
  "locations": [
    {
      "id": 1005,
      "name": "Storage A",
      "type": "STOR",
      "locations": [ ...(same schema as parent)... ],
      "inventories": [ ...(see below for schema)... ]
    },
    {
      "id": 1017,
      "name": "Storage B",
      "name": "COLD",
      "locations": [ ...(same schema as parent)... ],
      "inventories": [...(see below for schema)... ]
    }
  ],
  "inventories": [
    {
      "id": 5340,
      "product_id": 9120,
      "name": "Product X",
      "thumb": "https://example.com/api/images/nnnn.jpg",
      "sort_order": 1,
      "par_level": 3.5,
      "created": 1452898800,
      "updated": 1453071600,
      "measures": [
        {"id": 3498, "quantity": 2.25, "created": 1453071600, "updated": 1453071600},
        {"id": 3456, "quantity": 3.25, "created": 1452898800, "updated": 1452898800}
      ]
    }
  ]
}
+4
2

. -, . .

row_to_json json_agg.

- , row_to_json .

select json_agg(locations) from locations

json . , , , CTE . CTE .

, - :

WITH lowlevel1 AS 
( 
       SELECT a, 
          b, 
          c 
       FROM   tab1) ,lowlevel2 AS 
( 
       SELECT b, 
          c, 
          d 
       FROM   tab2) ,midlevel1 AS 
( 
        SELECT          e, 
                f, 
                g, 
                json_agg(lowlevel1) AS lab1, 
                json_agg(lowlevel2) AS lab2 
        FROM            tab3 
        LEFT OUTER JOIN lowlevel1 
        ON              tab3.id = lowlevel1.parent 
        LEFT OUTER JOIN lowlevel2 
        ON              tab3.id = lovlevel2.parent)
SELECT row_to_json(midlevel1) from midlevel1

json_agg(midlevel1) row_to_json(midlevel1), .

CTE RECURSIVE. , JSON. , , .

, Postgres null. , , , "locations":[null]. , case when <> then <> else '[]' end if <> then <> else '[]' end. - " ", .

+1

. , , . , JSON, , , , json_agg() 'ed.

CREATE OR REPLACE FUNCTION get_measures_by_inventory_as_json(invid UUID, del TIMESTAMP WITH TIME ZONE DEFAULT now())
RETURNS TABLE(inventory_id UUID, measure_json JSON)
AS $$
  -- returns a JSONified record per measure tied to an inventory record
  SELECT m.inventory_id, json_build_object(
    'id', m.id, 
    'quantity', m.quantity,
    'read', TRUNC(EXTRACT(EPOCH FROM m.read_date)),
    'created', TRUNC(EXTRACT(EPOCH FROM m.created)), 
    'updated', TRUNC(EXTRACT(EPOCH FROM m.updated)),
    'deleted', TRUNC(EXTRACT(EPOCH FROM m.deleted))
  )
  FROM measure m
  WHERE m.inventory_id = invid
  AND (m.deleted >= del);
$$
LANGUAGE sql;



CREATE OR REPLACE FUNCTION get_inventories_by_location_as_json(locid UUID, del TIMESTAMP WITH TIME ZONE DEFAULT now())
RETURNS TABLE(location_id UUID, inventory_json JSON)
AS $$
  -- returns a JSONified set of inventory items, with product info and measures, given a location
  SELECT i.location_id, json_build_object(
    'id', i.id,
    'product_id', p.id,
    'name', p.name,
    'mass_quantity', p.mass_quantity,
    'mass_unit', um.code,
    'count_unit', uc.code,
    'thumb', p.product_picture_uri,
    'sort_order', i.sort_order,
    'par_level', i.par_level,
    'created', TRUNC(EXTRACT(EPOCH FROM i.created)),
    'updated', TRUNC(EXTRACT(EPOCH FROM i.updated)),
    'deleted', TRUNC(EXTRACT(EPOCH FROM i.deleted)),
    'measures', COALESCE((SELECT json_agg(measure_json) FROM get_measures_by_inventory_as_json(i.id)), '[]')::json
  )
  FROM inventory i 
  INNER JOIN product p ON i.product_id = p.id
  LEFT JOIN unit um ON p.mass_unit_id = um.id
  LEFT JOIN unit uc ON p.count_unit_id = uc.id
  WHERE i.location_id = locid
  AND i.deleted >= del
  AND p.deleted >= del;
$$
LANGUAGE sql;



CREATE OR REPLACE FUNCTION get_inventories_recursive_as_json(locid UUID[], del TIMESTAMP WITH TIME ZONE DEFAULT now())
RETURNS JSON
AS $$
  -- returns JSONified location info and inventories in that location
  -- and recurses into child locations, showing the same
  SELECT json_agg(loc) FROM (
    SELECT l.id, array_agg(c.id), json_build_object(
    'id', l.id,
    'name', l.name,
    'type', t.code,
    'locations', get_inventories_recursive_as_json(array_agg(c.id)),
    'inventories', COALESCE((SELECT json_agg(inventory_json) FROM get_inventories_by_location_as_json(l.id)),'[]')::json
    ) AS loc
    FROM location l
    LEFT OUTER JOIN location c ON l.id = c.parent_id
    INNER JOIN location_type t ON l.location_type_id = t.id
    WHERE l.id = ANY(locid)
    AND l.deleted >= del
    GROUP BY l.id, l.name, t.code
  ) AS out;
$$
LANGUAGE sql;

CTE, , , , , .

WITH RECURSIVE locations AS (
  WITH inventories AS (
    WITH measures AS (
     SELECT m.inventory_id, json_agg(json_build_object(
        'id', m.id, 
        'quantity', m.quantity,
        'read', TRUNC(EXTRACT(EPOCH FROM m.read_date)),
        'created', TRUNC(EXTRACT(EPOCH FROM m.created)), 
        'updated', TRUNC(EXTRACT(EPOCH FROM m.updated)),
        'deleted', TRUNC(EXTRACT(EPOCH FROM m.deleted))
      )) as measures
      FROM measure m
      GROUP BY m.inventory_id
    )
    SELECT i.location_id, json_agg(json_build_object(
      'id', i.id,
      'product_id', p.id,
      'name', p.name,
      'mass_quantity', p.mass_quantity,
      'mass_unit', um.code,
      'count_unit', uc.code,
      'thumb', p.product_picture_uri,
      'sort_order', i.sort_order,
      'par_level', i.par_level,
      'created', TRUNC(EXTRACT(EPOCH FROM i.created)),
      'updated', TRUNC(EXTRACT(EPOCH FROM i.updated)),
      'deleted', TRUNC(EXTRACT(EPOCH FROM i.deleted)),
      'measures', COALESCE(m.measures, '[]')
    )) AS inventories
    FROM inventory i 
    INNER JOIN product p ON i.product_id = p.id
    LEFT JOIN unit um ON p.mass_unit_id = um.id
    LEFT JOIN unit uc ON p.count_unit_id = uc.id
    LEFT JOIN measures m ON i.id = m.inventory_id 
    GROUP BY i.location_id
  )

  SELECT null as id, null as name, null as type, null as inventories
  FROM location l
  INNER JOIN location_type t ON l.location_type_id = t.id
  LEFT OUTER JOIN inventories i ON l.id = i.location_id
  GROUP BY l.parent_id

  /*UNION ALL

  SELECT p.id, p.parent_id, p.name, t.code, COALESCE(i.inventories, '[]')::jsonb AS inventories, json_agg(row_to_json(c.*))
  FROM location p
  INNER JOIN location_type t ON p.location_type_id = t.id
  LEFT OUTER JOIN inventories i ON p.id = i.location_id
  INNER JOIN locations c ON p.id = c.parent_id
  GROUP BY p.id, p.name, t.code, COALESCE(i.inventories, '[]')::jsonb*/

)
SELECT * FROM locations
0

Source: https://habr.com/ru/post/1625029/

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