Adjacency list model duplicate parent & children - mysql

Question

Hierarchical Data in MySQL Using the Adjacency List Model
I have this table named node_structur_data
CREATE TABLE node_structure_data (
id INT(10) UNSIGNED NOT NULL AUTO_INCREMENT,
title VARCHAR(455) NOT NULL,
parent_id INT(10) UNSIGNED DEFAULT NULL,
PRIMARY KEY (id),
FOREIGN KEY (parent_id) REFERENCES node_structure_data (id)
ON DELETE CASCADE ON UPDATE CASCADE
);
Output:
id title parent_id
1 Division NULL
2 Site 1 1
3 Paper 2
4 ms1 3
How can I duplicate a node and its children?
For example Site 1
The id & parent_id should be unique but the title should stay the same.
Expected Output:
id title parent_id
1 Division NULL
2 Site 1 1
3 Paper 2
4 ms1 3
5 Site 1 1
6 Paper 5
7 ms1 6

Answer 1

The following approach first estimates the new max and then uses a recursive cte to find all children of the desired node 'Site 1' and determine their new possible parent_id if there were no other concurrent writes to the table.
I would recommend running the following in a transaction and locking the table during the operation to prevent concurrent table modifications.
To test this approach I added some additional sample data which I have included below, however you may see the approach in a demo with your initial sample data here
See output of working db fiddle below:
Schema (MySQL v8.0)
CREATE TABLE node_structure_data (
id INT(10) UNSIGNED NOT NULL AUTO_INCREMENT,
title VARCHAR(455) NOT NULL,
parent_id INT(10) UNSIGNED DEFAULT NULL,
PRIMARY KEY (id),
FOREIGN KEY (parent_id) REFERENCES node_structure_data (id)
ON DELETE CASCADE ON UPDATE CASCADE
);
INSERT INTO node_structure_data
(`id`, `title`, `parent_id`)
VALUES
('1', 'Division', NULL),
('2', 'Site 1', '1'),
('3', 'Paper', '2'),
('4', 'ms1', '3'),
('5', 'ms2', '3'),
('6', 'os1', '4'),
('7', 'os2', '4'),
('8', 'gs1', '1'),
('9', 'hs1', '3'),
('10','js1','9');
Query #1
select 'Before Insert';
Before Insert
Before Insert
Query #2
select * from node_structure_data;
id
title
parent_id
1
Division
2
Site 1
1
3
Paper
2
4
ms1
3
5
ms2
3
6
os1
4
7
os2
4
8
gs1
1
9
hs1
3
10
js1
9
Query #3
select 'Possible Data Changes';
Possible Data Changes
Possible Data Changes
Query #4
with recursive max_id AS (
SELECT MAX(id) as id FROM node_structure_data
),
child_nodes AS (
SELECT
n.id,
title,
parent_id,
m.id+1 as new_id,
parent_id as new_parent_id
FROM
node_structure_data n
CROSS JOIN
max_id as m
WHERE
title='Site 1'
UNION ALL
SELECT
n.id,
n.title,
n.parent_id,
#row_num:=IF(#row_num=0,c.new_id,0) + 1 + #row_num as new_id,
c.new_id
FROM
child_nodes c
INNER JOIN
node_structure_data n ON n.parent_id = c.id
CROSS JOIN (
SELECT #row_num:=0 as rn
) as vars
)
SELECT * FROM child_nodes;
id
title
parent_id
new_id
new_parent_id
2
Site 1
1
11
1
3
Paper
2
12
11
4
ms1
3
13
12
5
ms2
3
14
12
9
hs1
3
15
12
6
os1
4
16
13
7
os2
4
17
13
10
js1
9
18
15
Query #5 - Performing actual insert
INSERT INTO node_structure_data (title,parent_id)
with recursive max_id AS (
SELECT MAX(id) as id FROM node_structure_data
),
child_nodes AS (
SELECT
n.id,
title,
parent_id,
m.id+1 as new_id,
parent_id as new_parent_id
FROM
node_structure_data n
CROSS JOIN
max_id as m
WHERE
title='Site 1'
UNION ALL
SELECT
n.id,
n.title,
n.parent_id,
#row_num:=IF(#row_num=0,c.new_id,0) + 1 + #row_num as new_id,
c.new_id
FROM
child_nodes c
INNER JOIN
node_structure_data n ON n.parent_id = c.id
CROSS JOIN (
SELECT #row_num:=0 as rn
) as vars
)
SELECT title,new_parent_id FROM child_nodes ORDER BY new_id;
There are no results to be displayed.
Query #6
select 'AFTER INSERT';
AFTER INSERT
AFTER INSERT
Query #7
select * from node_structure_data;
id
title
parent_id
1
Division
2
Site 1
1
3
Paper
2
4
ms1
3
5
ms2
3
6
os1
4
7
os2
4
8
gs1
1
9
hs1
3
10
js1
9
11
Site 1
1
12
Paper
11
13
ms1
12
14
ms2
12
15
hs1
12
16
os1
13
17
os2
13
18
js1
15
View on DB Fiddle
Let me know if this works for you.