How to update FK linked to multiple table - Cascade on Update - mysql

Question

I have 3 tables which are linked to each other
task
client
compliance
The relationship is as shown in diagram below
The compliance table has the foreign key as below
The task table has the foreign key as below
Issue:
When I edit/update clientno in client table, I get
1452: Cannot add or update a child row: a foreign key constraint fails
(`task`, CONSTRAINT `task_ibfk_1` FOREIGN KEY (`officeid`, `clientid`) REFERENCES `client` (`officeid`, `clientno`) ON UPDATE CASCADE)
I expected that when clientno was changed in client table, the same will be updated in both complaince and task table.
I guess I am hitting a known limitation of InnoDB engine. Which goes not allow cascading updates to FK. If this is true, then what is the solution to updating the 3 tables with new clientno?
EDIT 1: As pointed out by #pankaj, how to overcome
If ON UPDATE CASCADE recurses to update the same table it has previously updated during the cascade, it acts like RESTRICT. This means that you cannot use self-referential ON UPDATE CASCADE operations. This is to prevent infinite loops resulting from cascaded updates.
Edit 2:
create table client
(
officeid char(6) not null,
clientno char(10) not null,
fname varchar(40) not null,
primary key (officeid, clientno)
);
create index officeid_clientno
on client (officeid, clientno);
create table compliance
(
officeid char(6) not null,
id smallint(5) unsigned not null,
clientid char(10) not null,
primary key (officeid, id),
constraint compliance_ibfk_2
foreign key (officeid, clientid) references client (officeid, clientno)
on update cascade
on delete cascade
);
create index officeid_clientid
on compliance (officeid, clientid, id);
create table task
(
officeid char(6) not null,
taskno char(10) not null,
clientid char(10) not null,
taskname varchar(50) not null,
complianceid smallint(5) unsigned null,
primary key (officeid, taskno),
constraint task_ibfk_1
foreign key (officeid, clientid) references client (officeid, clientno)
on update cascade,
constraint task_ibfk_4
foreign key (officeid, clientid, complianceid) references compliance (officeid, clientid, id)
on update cascade
);
create index officeid_clientid_complianceid
on task (officeid, clientid, complianceid);
FYI: I tried in mariadb 10.3 as well as mysql 8.0

Answer 1

The problem is related to the way relationships are declared.
First of all, as commented by #Nick, there is no need for a relation between task and client, as this is already covered by the relation to compliance. Commenting the declaration of this superfluous constraint is enough the make the error disappear, as you can see in this db fiddle.
create table task
(
officeid char(6) not null,
...
primary key (officeid, taskno),
-- constraint task_ibfk_1
-- foreign key (officeid, clientid) references client (officeid, clientno)
-- on update cascade,
constraint task_ibfk_4
foreign key (officeid, clientid, complianceid) references compliance (officeid, clientid, id)
on update cascade
);
Another suggestion is to use an autoincremented primary key in all tables (you can use an UNIQUE index to enforce composite referential integrity rules). This is the most usual way to proceed with MySQL, with which handling relationships is pretty straighforward.

Answer 2

I think that your problem stems from using mutable fields as primary keys
You can mitigate this by using a surrogate immutable primary key and adding a unique key to your mutable fields. You should be able to apply the same constraints as before without compromising data integrity
For example:
CREATE TABLE client (
id INT(10) UNSIGNED NOT NULL AUTO-INCREMENT PRIMARY,
officeid CHAR(6) NOT NULL,
clientno CHAR(10) NOT NULL,
fname VARCHAR(40) NOT NULL
);
CREATE UNIQUE INDEX uq-client-officeid-clientno IN client (officeid, clientno);
CREATE TABLE compliance (
id SMALLINT(5) UNSIGNED NOT NULL AUTO-INCREMENT PRIMARY,
client_id INT(10) UNSIGNED NOT NULL,
CONSTRAINT fk-compliance-client-id FOREIGN KEY id
REFERENCES client (id)
);
CREATE INDEX ix-compliance-id-client_id IN compliance (id, client_id);
CREATE TABLE task (
id INT(10) UNSIGNED NOT NULL AUTO-INCREMENT PRIMARY,
client_id INT(10) UNSIGNED NOT NULL,
compliance_id SMALLINT(5) UNSIGNED NULL,
taskno CHAR(10) NOT NULL,
taskname VARCHAR(50) NOT NULL,
CONSTRAINT fk-task-client-id FOREIGN KEY id
REFERENCES client (id),
CONSTRAINT fk-task-compliance-id-client_id FOREIGN KEY (compliance_id, client_id)
REFERENCES compliance (id, client_id)
);
This table structure mimics your current constraints and will allow you to update a clientno without needing the cascades
Note the foreign key fk-task-compliance-id-client_id which makes sure the compliance referenced by a task contains the correct client_id
I would also consider a separate table, office, with a surrogate integer primary key and containing the character based officeid. This could then be reference by the client table