PHP-ETL - Operations

Transform - Rule Engine – Data Transformation

The Rule Engine is a lightweight transformation component that converts an associative array into another associative array using a flexible set of rules.

It is designed to be used within PHP-ETL through the RuleTransformConfig.

Available Rules

Each rule defines how a specific value in the output array is computed. Rules can be nested and composed for complex transformations.

Expression Language (expression_language)

Leverages the Symfony Expression Language to compute values dynamically.

Value Fetcher (get)

Fetches a value from the input array by key.

Implode (implode)

Concatenates multiple values into a single string using a delimiter.

String To Lower (str_lower)

Converts a string to lowercase.

String To Upper (str_upper)

Converts a string to uppercase.

Constant (constant)

Returns a constant, static value.

Deprecated Rule

Condition (condition) – Deprecated

Deprecated: Use expression_language instead, which provides more powerful and flexible conditional logic.

A basic conditional evaluator for branching logic.

Example Use

Here’s an example of how to use rules to transform a CSV row:

operation: rule-engine-transformer
options:
  add: false
  columns:
    FullName:
      rules:
        - implode:
            values:
              - [{ get: { field: "FirstName" } }]
              - [{ get: { field: "LastName" } }]
            with: " "
    IsActive:
      rules:
        - expression_language:
            expression: "rowData['IsSubscribed'] == 'yes'"

Adding Your Own Rules

While PHP-ETL provides a powerful set of built-in rules, you may encounter situations where you need to implement your own custom logic. You can extend the RuleApplier class to add your own rules.

Here’s how you can create and use a custom rule:

1. Create a custom RuleApplier class:

First, create a new class that extends Oliverde8\Component\RuleEngine\RuleApplier.

<?php

namespace App\Etl\RuleEngine;

use Oliverde8\Component\RuleEngine\RuleApplier;

class CustomRuleApplier extends RuleApplier
{
    public function apply($data, $rowData, $params)
    {
        // Implement your custom rule logic here.
        return "new value";
    }
}

2. Register your custom RuleApplier with the ChainBuilderV2:

When creating your ChainBuilderV2, pass your custom RuleApplier to the GenericChainFactory for RuleTransformConfig.

<?php

use App\Etl\RuleEngine\CustomRuleApplier;
use Oliverde8\Component\PhpEtl\ChainBuilderV2;
use Oliverde8\Component\PhpEtl\ChainConfig;
use Oliverde8\Component\PhpEtl\ChainOperation\Transformer\RuleTransformOperation;
use Oliverde8\Component\PhpEtl\OperationConfig\Transformer\RuleTransformConfig;
use Oliverde8\Component\PhpEtl\Builder\Factories\GenericChainFactory;

$customRuleApplier = new CustomRuleApplier();

$chainBuilder = new ChainBuilderV2([
    new GenericChainFactory(
        RuleTransformOperation::class,
        RuleTransformConfig::class,
        injections: ['ruleApplier' => $customRuleApplier]
    ),
    // ... other factories
]);

// Use the custom rule in your chain
$chainConfig = new ChainConfig();
$chainConfig->addLink((new RuleTransformConfig(add: false))
    ->addColumn('MyCustomField', [
        ['myCustomRule' => [
            'field1' => ['get' => ['field' => 'FirstName']],
            'field2' => ['get' => ['field' => 'LastName']],
        ]]
    ])
);

$processor = $chainBuilder->createChain($chainConfig);

services:
  App\Etl\RuleEngine\CustomRuleApplier:
    class: App\Etl\RuleEngine\CustomRuleApplier
    autowire: true
    tags:
      - { name: etl.rule }

  # The GenericChainFactory will automatically use your custom RuleApplier
  # when it's injected via dependency injection

3. Use your custom rule in your chain configuration:

Once you have configured your ChainBuilderV2 to use your custom RuleApplier, you can use your custom rule in your chain.

$chainConfig = new ChainConfig();
$chainConfig->addLink((new RuleTransformConfig(add: false))
    ->addColumn('MyCustomField', [
        ['myCustomRule' => [
            'field1' => ['get' => ['field' => 'FirstName']],
            'field2' => ['get' => ['field' => 'LastName']],
        ]]
    ])
);