How to model ownership of a resource (e.g. credit card) - sql

Question

I'm trying to figure out how to model ownership of a resource. An example can be a credit card. In a scenario a credit card can be owned by a company, a business or a business_admin which is used to pay for a service that belongs to a business.
What I came up with is a table business_payment that references company_payment_method, business_payment_method, business_admin_payment_method as well as the business that gets the payment method assigned. They are all nullable which requires a trigger to check if the insert is valid - exactly one ID must be not null before insert:
CREATE TABLE business_payment (
business_id BIGINT NOT NULL,
CONSTRAINT fk__business_payment__business
FOREIGN KEY (business_id)
REFERENCES business(id)
ON DELETE CASCADE,
company_payment_method_id BIGINT,
CONSTRAINT fk__business_payment__company_payment_method
FOREIGN KEY (company_payment_method_id)
REFERENCES company_payment_method(id)
ON DELETE CASCADE,
business_payment_method_id BIGINT,
CONSTRAINT fk__business_payment__business_payment_method
FOREIGN KEY (business_payment_method_id)
REFERENCES business_payment_method(id)
ON DELETE CASCADE,
business_admin_payment_method_id BIGINT,
CONSTRAINT fk__business_payment__business_admin_payment_method
FOREIGN KEY (business_admin_payment_method_id)
REFERENCES business_admin_payment_method(id)
ON DELETE CASCADE
);
Pro:
The advantage I see here is that if any of the credit cards are deleted e.g.
DELETE FROM company_credit_card WHERE id = #companyCreditCardId;
also the business_payment_method will get deleted. On the application layer nobody has to take care of the cleaning this up.
Con:
On the other hand I now have a table which has NULL values and if Ever there was a new entity x_credit_card I'd have to add this column to this table as well as make sure the trigger does its job correctly.
So this is the solution I was thinking about but I'm not sure if this is very elegant - especially because I'm creating an M*N matrix with (M*N - M) NULL entries.
Can I do better than this setup?
Below is the complete code if you want to check it out. Unfortunately I can't make it run on SQLFiddle because of this DELIMITER thing.
DROP TABLE IF EXISTS company_business;
DROP TABLE IF EXISTS company_employee;
DROP TABLE IF EXISTS payment_method;
DROP TABLE IF EXISTS business_payment;
DROP TABLE IF EXISTS business_admin_payment_method;
DROP TABLE IF EXISTS company_payment_method;
DROP TABLE IF EXISTS business_payment_method;
DROP TABLE IF EXISTS company;
DROP TABLE IF EXISTS business_admin;
DROP TABLE IF EXISTS business;
CREATE TABLE company (
id BIGINT AUTO_INCREMENT PRIMARY KEY
);
CREATE TABLE business_admin (
id BIGINT AUTO_INCREMENT PRIMARY KEY
);
CREATE TABLE business (
id BIGINT AUTO_INCREMENT PRIMARY KEY
);
CREATE TABLE company_employee (
company_id BIGINT NOT NULL,
CONSTRAINT fk__company_employee__company
FOREIGN KEY (company_id)
REFERENCES company(id)
ON DELETE CASCADE,
business_admin_id BIGINT NOT NULL,
CONSTRAINT fk_company_employee__business_admin
FOREIGN KEY (business_admin_id)
REFERENCES business_admin(id)
ON DELETE CASCADE,
PRIMARY KEY (company_id, business_admin_id)
);
CREATE TABLE company_business (
company_id BIGINT NOT NULL,
CONSTRAINT fk__company_business__company
FOREIGN KEY (company_id)
REFERENCES company(id)
ON DELETE CASCADE,
business_id BIGINT NOT NULL,
CONSTRAINT fk__company_business__business
FOREIGN KEY (business_id)
REFERENCES business(id)
ON DELETE CASCADE,
PRIMARY KEY (company_id, business_id)
);
SET #businessAdminId1 = 1;
INSERT INTO business_admin(id) VALUES (#businessAdminId1);
SET #companyId1 = 1;
INSERT INTO company(id) VALUES (#companyId1);
INSERT INTO company_employee(company_id, business_admin_id) VALUES (#companyId1,#businessAdminId1);
SET #businessId1 = 1;
INSERT INTO business VALUES (#businessId1);
INSERT INTO company_business VALUES(#companyId1, #businessId1);
CREATE TABLE company_payment_method (
id BIGINT AUTO_INCREMENT PRIMARY KEY,
company_id BIGINT NOT NULL,
CONSTRAINT fk__company_payment_method__company
FOREIGN KEY (company_id)
REFERENCES company(id)
ON DELETE CASCADE,
payment_method_token VARCHAR(128) NOT NULL
);
CREATE TABLE business_payment_method (
id BIGINT AUTO_INCREMENT PRIMARY KEY,
business_id BIGINT NOT NULL,
CONSTRAINT fk__business_payment_method__business
FOREIGN KEY (business_id)
REFERENCES business(id)
ON DELETE CASCADE,
payment_method_token VARCHAR(128) NOT NULL
);
CREATE TABLE business_admin_payment_method (
id BIGINT AUTO_INCREMENT PRIMARY KEY,
business_admin_id BIGINT NOT NULL,
CONSTRAINT fk__business_admin_payment_method__business_admin
FOREIGN KEY (business_admin_id)
REFERENCES business_admin(id)
ON DELETE CASCADE,
payment_method_token VARCHAR(128) NOT NULL
);
CREATE TABLE business_payment (
business_id BIGINT NOT NULL,
CONSTRAINT fk__business_payment__business
FOREIGN KEY (business_id)
REFERENCES business(id)
ON DELETE CASCADE,
company_payment_method_id BIGINT,
CONSTRAINT fk__business_payment__company_payment_method
FOREIGN KEY (company_payment_method_id)
REFERENCES company_payment_method(id)
ON DELETE CASCADE,
business_payment_method_id BIGINT,
CONSTRAINT fk__business_payment__business_payment_method
FOREIGN KEY (business_payment_method_id)
REFERENCES business_payment_method(id)
ON DELETE CASCADE,
business_admin_payment_method_id BIGINT,
CONSTRAINT fk__business_payment__business_admin_payment_method
FOREIGN KEY (business_admin_payment_method_id)
REFERENCES business_admin_payment_method(id)
ON DELETE CASCADE
);
DELIMITER //
CREATE TRIGGER before_insert_business_payment_method BEFORE INSERT ON business_payment
FOR EACH ROW BEGIN
DECLARE notNullForeignKeyFound BOOLEAN;
DECLARE errorMessage VARCHAR(100);
SET errorMessage = 'Exact one foreign key must be not null!';
SET notNullForeignKeyFound = FALSE;
-- Company credit card ID
IF NEW.company_payment_method_id IS NOT NULL THEN
SET notNullForeignKeyFound = TRUE;
END IF;
-- Business credit card ID
IF NEW.business_payment_method_id IS NOT NULL THEN
IF notNullForeignKeyFound IS TRUE THEN
SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = errorMessage;
END IF;
SET notNullForeignKeyFound = TRUE;
END IF;
-- Business admin credit card ID
IF NEW.business_admin_payment_method_id IS NOT NULL THEN
IF notNullForeignKeyFound IS TRUE THEN
SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = errorMessage;
END IF;
SET notNullForeignKeyFound = TRUE;
END IF;
-- Check if at least one ID is not null
IF notNullForeignKeyFound IS FALSE THEN
SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = errorMessage;
END IF;
END//
DELIMITER ;
SET #companyCreditCardId1 = 1;
INSERT INTO company_payment_method (id, company_id, payment_method_token) VALUES (#companyCreditCardId1, #companyId1, 'wergef');
SET #businessCreditCardId1 = 1;
INSERT INTO business_payment_method (id, business_id, payment_method_token) VALUES (#businessCreditCardId1, #businessId1, 'asjio');
--
-- Here comes the actual action ..
--
-- Succeeds
INSERT INTO business_payment (business_id, business_payment_method_id) VALUES (#businessId1, #companyCreditCardId1);
-- Fails
-- INSERT INTO business_payment (business_id, company_payment_method_id, business_payment_method_id) VALUES (#businessId1, #companyCreditCardId1, #businessCreditCardId1);
-- The following will delete:
-- + business_payment_method.payment_method_id = 1
-- + busuiness_payment_method.payment_method_id = 1
DELETE FROM business_payment_method WHERE id = #companyCreditCardId1;

Answer 1

Another way would be for you to have a business_entity table with an entity_type(business, employee, admin, etc.). Payment could have a single Foreign Key back to entity. You would then have a detail table for each entity type that would have the detail information for that particular type of entity.
business_entity--1----M--business_payment
| |--1-----1--employee
|--1-------1--admin