Question

I have been working with a small team on a small project about fiction world building. I have been assigned with the task of managing triggers/chained behavior of entities (rocks/places/items) that can be triggered in many ways such as throwing a magic rock into the lake and monster X will appear, and continue to trigger the things in a chain until it reaches the end.

I have tried this

$Trigger_123 = new stdClass();
$Trigger_123->name = "Name";
$Trigger_123->renderOn = ? // (object_345->throwedInLakeX) ?

How can I store this in MySQL? Can I have it checked if its a chain part? Also I tried MySQL triggers but I can’t find a way to execute PHP on those triggers. Running PHP code on update or delete for example.

Cron jobs was not a option because many things will be added in the future and cron jobs will take a lot of time to finish, I was hoping of finding a more php-based solution.

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Edited (adding some additional information)

I tried to implement this in many ways. I ended up with a system of dependecies pretty much like debian packages which I believe is not suited for this.

Database structure

Table "object"
--------------
ID (int)
Name (varchar)

Table "triggers"
----------------
ID (int)
Name (varchar)
Data (blob) // usually, I store php code and use eval to run

Table "attributes"
------------------
ID (int)
attribute (varchar)
value (blob)

Table "object_has_triggers"
---------------------------
ID (int)
ObjectID (int)
TriggerID (int)

Table "object_has_attributes"
-----------------------------
ID (int)
ObjectID (int)
AttributeID (int)

What I want as a result is to make a PHP code snippet execute each time

• A database transaction , before is submitted and after to database
• A object that has X triggers attached to it, resolve them
• Each Trigger that is triggered by X be checked if all dependecies to it are satisfied

Question:
Is something like this even possible to build with PHP Or should I try other scripting languages like python?

Answer 1

A PHP code snippet execute each time a database transaction , before is submitted and after to database

Don’t reinvent the wheel, this has an incredible simple solution: have a layer on top of your database calls.

Instead of querying your database directly, call a function (perhaps in an object) that handles the database insertion of triggers. And it is right there that you can add your code to pre and post- process your triggers in whichever way you please.

function processDatabaseInsertion($trigger) {
    //Preceding code goes here

    //Database transaction goes here

    //Post-processing code goes here
}

$Trigger_123 = new stdClass();
$Trigger_123->name = "Name";
$Trigger_123->renderOn = $object_345->throwedInLakeX;

processDatabaseInsertion($Trigger_123);

Over simplified, but you get the idea. I would recommend writing a custom class for your triggers but I wrote it in a procedural style since I don’t know if you are familiar with OOP.

A PHP code snippet execute each time a object that has X triggers attached to it, resolve them

Same principle as before. If you use PHP >= 5.3, you can spice it up a bit using closures:

function processDatabaseInsertion($trigger) {
    //Preceding code goes here
    $trigger->renderOn();

    //Database transaction goes here

    //Post-processing code goes here
}

$Trigger_123 = new stdClass();
$Trigger_123->name = "Name";
$Trigger_123->renderOn = function() use ($Trigger_123) { doAwesomeThing($Trigger_123); }

processDatabaseInsertion($Trigger_123);

Or otherwise go for a more traditional approach:

function processDatabaseInsertion($trigger) {
    //Preceding code goes here
    switch($trigger->renderOn) {
        case "awesomeThing":
            doAwesomeThing($trigger);
            break;
        case "anotherThing":
            break;
        default:
            break;
    }


    //Database transaction goes here

    //Post-processing code goes here
}

$Trigger_123 = new stdClass();
$Trigger_123->name = "Name";
$Trigger_123->renderOn = "awesomeThing";

processDatabaseInsertion($Trigger_123);

Each Trigger that is triggered by X be checked if all dependecies to
it are satisfied

Can easily be handled by the methods above with some more PHP logic as you will be able to tell. You may want to have for instance a generic function called every time you need to process a trigger which in turns check if dependencies are satistifed and runs the specific trigger if so.

Either way there are better ways to tackle this problem than to use eval or some mysql trigger hacking as you can see 🙂