Question

I need to build an app (PHP/MySQL but I don’t think it matters), letting a user to input a set of rules matching particular products. That should look like a form, allowing to select a key and to input its value, but supporting grouping with OR and AND statements. For example the user should be able to input the following product rules: (price over 100 and red color) or (price over 50 and green color), weight over 2 and so on. The problem is, I’m not sure how should I store that in the database and not sure how to code UI for that. Is there any common approach to solving such a problem?

Thanks

Answer 1

I’ve been thinking about that for a while. Here’s what I came to:

There is a rule table:

rule_id int,
field1 varchar,
rule1_id int,
operand varchar, --whatever, can be int, if operand is described in other table.
field2 varchar,
rule2_id int

Your example rule can be expressed in this way:

rule_id  field1   rule1_id      operand     field2      rule2_id
1       'price'     null            '>'       '100'       null
2       'color'     null            '='       'red'       null
3       null        1               'and'     null        2
4       'price'     null            '>'       '50'        null
5      'color'    null            '='       'green'     null
6       null        4               'and'     null        5
7       null        3               'or'      null        6

You will then be referencing the complex rule with rule_id=7. To resolve that rule, each other rule should be resolved recursively. field can be a field in a database, as well as the operand. You would then be able to form SQL queries from this saved data. It’s also easy to load and present into controls, so the user can edit this rule using combo boxes (HTML <select>) and stuff.