User role permissions for different modules using bitwise operators - php

Question

So I have an application that has several modules (think of modules as different pages), each module has a set of permissions; view, add, edit, delete
I want each user role to have privileges for each module, for example
Role A Permissions
Module 1 -> view
Module 2 -> add, edit
Module 3 -> view, add, edit, delete
etc.
How can I design the database to support that and how would I go about implementing it using bitwise operators (or would there be a more efficient way for this particular case?)
I already have the user, user_role and role tables but I'm unsure on how to design the Module table.

Answer 1

Here I am showing how we can implement it with Mysql.
Below is a sample tables with some sample data:
Table 1 : Permission table to store permission name along with it bit like 1,2,4,8..etc (multiple of 2)
CREATE TABLE IF NOT EXISTS `permission` (
`bit` int(11) NOT NULL,
`name` varchar(50) NOT NULL,
PRIMARY KEY (`bit`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
Insert some sample data into the table.
INSERT INTO `permission` (`bit`, `name`) VALUES
(1, 'User-Add'),
(2, 'User-Edit'),
(4, 'User-Delete'),
(8, 'User-View'),
(16, 'Blog-Add'),
(32, 'Blog-Edit'),
(64, 'Blog-Delete'),
(128, 'Blog-View');
Table 2: User table to store user id,name and role. Role will be calculated as sum of permissions.
Example :
If user 'Ketan' having permission of 'User-Add' (bit=1) and 'Blog-Delete' (bit-64) so role will be 65 (1+64).
If user 'Mehata' having permission of 'Blog-View' (bit=128) and 'User-Delete' (bit-4) so role will be 132 (128+4).
CREATE TABLE IF NOT EXISTS `user` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(50) NOT NULL,
`role` int(11) NOT NULL,
`created_date` datetime NOT NULL
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
Sample data-
INSERT INTO `user` (`id`, `name`, `role`, `created_date`)
VALUES (NULL, 'Ketan', '65', '2013-01-09 00:00:00'),
(NULL, 'Mehata', '132', '2013-01-09 00:00:00');
Loding permission of user
After login if we want to load user permission than we can query below to get the permissions:
SELECT permission.bit,permission.name
FROM user LEFT JOIN permission ON user.role & permission.bit
WHERE user.id = 1
Here user.role "&" permission.bit is a Bitwise operator which will give output as -
User-Add - 1
Blog-Delete - 64
If we want to check whether a particular user have user-edit permission or not-
SELECT * FROM `user`
WHERE role & (select bit from permission where name='user-edit')
Output = No rows.
Click here for more information.

Answer 2

If you decide to use a bitmask, remember that the number of permissions you can keep track of is limited (you can track 31 permissions in a signed 4-byte integer database column). Each permission would then be assigned a value that is a power of two (1, 2, 4, 8, etc), and you could perform bitwise operations to check for permission matches.
From what you're looking to accomplish, I would suggest creating a role_has_module_privs table instead. This approach is much more scalable, and more efficient from a querying perspective. But if you have a finite number of combinations, bitmasks may be more efficient.