README

Balance Accounting System extension for Yii2

This extension provides basic support for balance accounting (bookkeeping) system based on debit and credit principle.

For license information check the LICENSE-file.

Installation

The preferred way to install this extension is through composer.

Either run

php composer.phar require --prefer-dist yii2tech/balance

or add

"yii2tech/balance": "*"

to the require section of your composer.json.

Usage

This extension provides basic support for balance accounting (bookkeeping) system based on debit and credit principle. Balance system is usually used for the accounting (bookkeeping) and money operations. However, it may also be used for any resource transferring from one location to another. For example: transferring goods from storehouse to the shop and so on.

There 2 main terms related to the balance system:

account - virtual storage of the resources, which have some logical meaning.
transaction - represents actual transfer of the resources to or from particular account.

Lets assume we have a system, which provides virtual money balance for the user. Money on the balance can be used for the goods purchasing, user can top up his balance via some payment gateway. In such example, each user should have 3 virtual balance accounts: 'virtual-money', 'payment-gateway' and 'purchases'. When user tops up his virtual balance, our system should remove money from 'payment-gateway' and add them to 'virtual-money'. When user purchases an item, our system should remove money from 'virtual-money' and add them to 'purchases'. The trick is: if you sum current amount over all user related accounts ('payment-gateway' + 'virtual-money' + 'purchases'), it will always be equal to zero. Such check allows you to verify if something went wrong any time.

This extension introduces term 'balance manager' as a Yii application component, which should handle all balance transactions. Several implementations of such component are provided:

[[yii2tech\balance\ManagerDb]] - uses a relational database as a data storage.
[[yii2tech\balance\ManagerMongoDb]] - uses MongoDB as a data storage.
[[yii2tech\balance\ManagerActiveRecord]] - uses ActiveRecord classes for the data storage.

Please refer to the particular manager class for more details.

You can use balance manager as standalone object or configure it as application component. Application configuration example:

return [
    'components' => [
        'balanceManager' => [
            'class' => 'yii2tech\balance\ManagerDb',
            'accountTable' => '{{%BalanceAccount}}',
            'transactionTable' => '{{%BalanceTransaction}}',
            'accountLinkAttribute' => 'accountId',
            'amountAttribute' => 'amount',
            'dataAttribute' => 'data',
        ],
    ],
    ...
];

In order to increase (debit) balance at particular account, [[\yii2tech\balance\ManagerInterface::increase()]] method is used:

Yii::$app->balanceManager->increase($accountId, 500); // add 500 credits to account

In order to decrease (credit) balance at particular account, [[\yii2tech\balance\ManagerInterface::decrease()]] method is used:

Yii::$app->balanceManager->decrease($accountId, 100); // remove 100 credits from account

Tip: actually, method decrease() is redundant, you can call increase() with negative amount in order to achieve same result.

It is unlikely you will use plain increase() and decrease() methods in your application. In most cases there is a need to transfer money from one account to another at once. Method [[\yii2tech\balance\ManagerInterface::transfer()]] can be used for this:

$fromId = 1;
$toId = 2;
Yii::$app->balanceManager->transfer($fromId, $to, 100); // remove 100 credits from account 1 and add 100 credits to account 2

Note that method transfer() creates 2 separated transactions: one per each affected account. Thus you can easily fetch all money transfer history for particular account, simply selecting all transactions linked to it. 'Debit' transactions will have positive amount, while 'credit' ones - negative.

Note: If you wish each transaction created by transfer() remember another account involved in the process, you'll need to setup [[\yii2tech\balance\Manager::$extraAccountLinkAttribute]].

You may revert particular transaction using [[\yii2tech\balance\ManagerInterface::revert()]] method:

Yii::$app->balanceManager->revert($transactionId);

This method will not remove original transaction, but create new one, which compensates it.

Querying accounts

Using account IDs for the balance manager is not very practical. In our above example, each system user have 3 virtual accounts, each of which has its own unique ID. However, while performing purchase we operating user ID and account type, so we need to query actual account ID before using balance manager. Thus there is an ability to specify account for the balance manager methods using their attributes set. For example:

Yii::$app->balanceManager->transfer(
    [
        'userId' => Yii::$app->user->id,
        'type' => 'virtual-money',
    ],
    [
        'userId' => Yii::$app->user->id,
        'type' => 'purchases',
    ],
    500
);

In this example balance manager will find ID of the affected accounts automatically, using provided attributes as a filter.

You may enable [[yii2tech\balance\Manager::$autoCreateAccount]], allowing automatic creation of the missing accounts, if they are specified as attributes set. This allows accounts creation on the fly, by demand only, eliminating necessity of their pre-creation.

Heads up! Actually 'account' entity is redundant at balance system, and its usage can be avoided. However, its presence provides more flexibility and saves performance. Storing of account data is not mandatory for this extension, you can configure your balance manager in the way it is not used.

Finding account current balance

Current money amount at particular account can always be calculated as a sum of amounts over related transactions. You can use [[\yii2tech\balance\ManagerInterface::calculateBalance()]] method for that:

Yii::$app->balanceManager->transfer($fromAccount, $toAccount, 100); // assume this is first time accounts are affected

echo Yii::$app->balanceManager->calculateBalance($fromAccount); // outputs: -100
echo Yii::$app->balanceManager->calculateBalance($toAccount); // outputs: 100

However, calculating current balance each time you need it, is not efficient. Thus you can specify an attribute of account entity, which will be used to store current account balance. This can be done via [[\yii2tech\balance\Manager::$accountBalanceAttribute]]. Each time balance manager performs a transaction it will update this attribute accordingly:

use yii\db\Query;

Yii::$app->balanceManager->transfer($fromAccountId, $toAccountId, 100); // assume this is first time accounts are affected

$currentBalance = (new Query())
    ->select(['balance'])
    ->from('BalanceAccount')
    ->andWhere(['id' => $fromAccountId])
    ->scalar();

echo $currentBalance; // outputs: -100

Saving extra transaction data

Usually there is a necessity to save extra information along with the transaction. For example: we may need to save payment ID received from payment gateway. This can be achieved in following way:

// simple increase :
Yii::$app->balanceManager->increase(
    [
        'userId' => Yii::$app->user->id,
        'type' => 'virtual-money',
    ],
    100,
    // extra data associated with transaction :
    [
        'paymentGateway' => 'PayPal',
        'paymentId' => 'abcxyzerft',
    ]
);

// transfer :
Yii::$app->balanceManager->transfer(
    [
        'userId' => Yii::$app->user->id,
        'type' => 'payment-gateway',
    ],
    [
        'userId' => Yii::$app->user->id,
        'type' => 'virtual-money',
    ],
    100,
    // extra data associated with transaction :
    [
        'paymentGateway' => 'PayPal',
        'paymentId' => 'abcxyzerft',
    ]
);

The way extra attributes are stored in the data storage depends on particular balance manager implementation. For example: [[\yii2tech\balance\ManagerDb]] will try to store extra data inside transaction table columns, if their name equals the parameter name. You may as well setup special data field via [[\yii2tech\balance\ManagerDb::$dataAttribute]], which will store all extra parameters, which have no matching column, in serialized state.

Note: watch for the keys you use in transaction data: make sure they do not conflict with columns, which are reserved for other purposes, like primary keys.

Events

[[\yii2tech\balance\Manager]] provide several events, which can be handled via event handler or behavior:

[[yii2tech\balance\Manager::EVENT_BEFORE_CREATE_TRANSACTION]] - raised before creating new transaction.
[[yii2tech\balance\Manager::EVENT_AFTER_CREATE_TRANSACTION]] - raised after creating new transaction.

For example:

use yii2tech\balance\Manager;
use yii2tech\balance\ManagerDb;

$manager = new ManagerDb();

$manager->on(Manager::EVENT_BEFORE_CREATE_TRANSACTION, function ($event) {
    $event->transactionData['amount'] += 10; // you may adjust transaction data to be saved, including transaction amount
    $event->transactionData['comment'] = 'adjusted by event handler';
});

$manager->on(Manager::EVENT_AFTER_CREATE_TRANSACTION, function ($event) {
    echo 'new transaction: ' $event->transactionId; // you may get newly created transaction ID
});

$manager->increase(1, 100); // outputs: 'new transaction: 1'
echo Yii::$app->balanceManager->calculateBalance(1); // outputs: 110

yii2tech / balance

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