[RESOLVED] storing binary permissions in mysql

sfullman

Hi,

it would be nice to know how to query mysql for a permission directly.

I'm planning to store 5 different permissions (true or false) for each in one field as a binary number

1 = ( 1 base 10) = permission #1
10 = ( 2 base 10) = permission #2
100= ( 4 base 10) = ..
1000=(8 base 10)= ..
10000=16 base 10 = permission #5

but i would store it in a field ranging in value from 0 to 32, or in base 2 from

00000

11111

my question is, how using mysql do I get this equivalent?

"SELECT FROM permissions_table WHERE HAS_PRIVILEGE(permission_field, 8 /* permission#4 */)"

I am pretty sure this is possible but it's been maybe a year since I've seen an example.

Samuel

bradgrafelman

You could use the Bit Functions (although by "functions" I think one would call them "operators", e.g. the bitwise operators in PHP) if you realize that your table should instead look like:

[pre]1 = 1 = permission #1
10 = 2 = permission #2
100 = 4 = permission #3
1000 = 8 = permission #4
10000 = 16 = permission #5[/pre]
Thus, if the permissions field had a value of 21, you know that the user has permissions #1, 3, and 5.

You could check for say permission #5 by doing something like "permission_field & 16" (if the result is non-zero, then the user does have that permission).

EDIT: Seems like a good place for this joke as well: There are 10 kinds of people in the world: those who can count in binary and those who can not.

sfullman

yes is was the

field & n

comparison which I needed to read that field where n is a number which should be in field - thanks

OK, so why can they never solve redneck murders?

A: 1. there are no teeth for dental records
2. the DNA is all the same

I do hope you know what a redneck is..