README

Transact is a transaction library for PHP similar to the way database transactions work but for PHP code.

The purpose is to be able to execute multiple actions which might depend on the previous action completing successfully before eexecuting the next one and in case of failure you want to revert back to the original state.

Installation

Use the following composer command to install

composer require asimlqt/transact

Example

The following example creates 3 simple actions that echo some text during the execute and revert methods. This example will be referenced throughout the rest of the README and only changes will be listed.

use Asimlqt\Transact\TransactionManager;
use Asimlqt\Transact\Action;
use Asimlqt\Transact\TransactionFailedException;

$transactionManager = new TransactionManager();

class Action1 extends Action {
    public function execute() {
        echo "Action1 execute\n";
    }
    public function revert() {
        echo "Action1 revert\n";
    }
}

class Action2 extends Action {
    public function execute() {
        echo "Action2 execute\n";
    }
    public function revert() {
        echo "Action2 revert\n";
    }
}

class Action3 extends Action {
    public function execute() {
        echo "Action3 execute\n";
    }
    public function revert() {
        echo "Action3 revert\n";
    }
}

$transactionManager
    ->addAction(new Action1())
    ->addAction(new Action2())
    ->addAction(new Action3());

try {
    $transactionManager->execute();
    echo "Transaction completed successfully\n";
} catch (TransactionFailedException $e) {
    echo $e->getMessage() . "\n";
}

The output of the program is

Action1 execute
Action2 execute
Action3 execute
Transaction completed successfully

Order of execution

The actions are executed in the order they are added. When there is an error i.e. when an exception is thrown the revert methods will be called in reverse order. The revert method of the last successful action will be called first then the one before that etc. all the way to the first action.

For example if the third action threw an exception then the revert method of Action2 will be called then the revert method of Action1:

class Action3 extends Action {
    public function execute() {
        echo "Action3 execute\n";
        throw new Exception();
    }
    public function revert() {
        echo "Action3 revert\n";
    }
}

The output of will be:

Action1 execute
Action2 execute
Action3 execute
Action2 revert
Action1 revert
Transaction failed

You've probably noticed that the Action3 execute method through an exception so why wasn't the revert method of Action3 called? That's becasue each action should perform only one task, so if an action threw an exception becasue it couldn't complete the task then there is nothing to revert!

Passing data to actions

Usually the actions will need some data to perform their tasks so to do this use the Intent object which is a simple wrapper around an array. It only has 2 methods get and set. This will automatically be injected into the actions before the execute method is called.

$intent = new Asimlqt\Transact\Intent();
$intent->set("user", $user);
$transactionManager->setIntent($intent);

Then in the Action you can retrieve the user using:

    public function execute() {
        $user = $this->getIntent()->get("user");
        ...
    }

Note that the same intent object will be forwarded to all actions so it is possible to overwrite data. It can also be useful if you need to pass data from one action to another.

Retry Policies

If an action fails to complete it's task due to some external factor you might want to try the action again e.g. making an API request. Retry policies can be specified for both, execute and revert. They are action specific so you can only specify a retry policy for only one action or different policies for different actions. The following policies are currently available:

RetryNone

This is the default policy if you don't explicitly specify one. this does not perform any retries.

RetryOnce

This will immediately try the action again before marking it as failed.

RetryNumTimes

This will try the action repeatedly for the specified number of times.

RetryAfter

This will retry the request once more after a delay of specified microseconds.

You will need to set these on the Action objects before adding them to the transaction manager:

$action1 = new Action1();
$action1->setExecuteRetryPolicy(new Asimlqt\Transact\Retry\RetryOnce());
$transactionManager->addAction($action1);

asimlqt / transact

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