Enhancing Data Management: Virtual Columns in Laravel with MariaDB

In Laravel, virtual columns, also known as generated columns, are a database feature that allows you to define a column's value based on an expression involving other columns in your table. This expression is evaluated by the database engine (MariaDB in this case) whenever the table is queried, providing a convenient way to calculate and display derived data without storing it explicitly.

Adding a Virtual Column with Schema Builder

Laravel's schema builder offers the virtualAs method to define virtual columns within your migrations. Here's a step-by-step guide:

1. Create a Migration:

2. Define the Virtual Column:

   • Inside the up method of your migration, use the virtualAs method on the Schema builder facade:

   Schema::table('<table_name>', function (Blueprint $table) {
       $table->virtualAs('<virtual_column_name>', '<expression>');
   });
   

   • Replace the following placeholders:
     • <table_name>: The name of the table where you want to add the virtual column.
     • <virtual_column_name>: The name you want to give to the virtual column.
     • <expression>: The SQL expression that defines how the virtual column's value is calculated. This expression can involve other columns in the table and mathematical or string manipulation functions supported by MariaDB.

Example:

Let's say you have a products table with columns for quantity and unit_price. You want to add a virtual column named total_price that calculates the product of quantity and unit_price.

public function up()
{
    Schema::table('products', function (Blueprint $table) {
        $table->virtualAs('total_price', 'quantity * unit_price');
    });
}

Accessing Virtual Columns

Virtual columns are not stored in the database itself. However, you can access their calculated values in your Laravel application using Eloquent or raw SQL queries.

Using Eloquent:

$product = Product::find(1);
echo $product->total_price; // This will evaluate the expression and return the calculated value

Using Raw SQL:

SELECT *, total_price FROM products;

Important Notes:

• Virtual columns are not persisted to the database, so they are not included in backups or replicated to slave databases.
• Indexes cannot be created on virtual columns in MariaDB.

<?php

use Illuminate\Support\Facades\Schema;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Database\Migrations\Migration;

class AddVirtualColumnToProductsTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::table('products', function (Blueprint $table) {
            // Add virtual column for total price
            $table->virtualAs('total_price', 'quantity * unit_price');

            // Example of adding a virtual column with a more complex expression
            // (assuming you have a 'discount' column for percentage discounts)
            $table->virtualAs('discounted_price', 'quantity * unit_price * (1 - discount / 100)');
        });
    }

    /**
     * Reverse the migrations.
     *
     * @return void
     */
    public function down()
    {
        Schema::table('products', function (Blueprint $table) {
            $table->dropVirtual('total_price');
            $table->dropVirtual('discounted_price'); // If you added the second virtual column
        });
    }
}

Explanation:

1. Import Necessary Classes:

   • Schema: Provides access to database schema manipulation methods.
   • Blueprint: Defines the structure of a database table.
   • Migration: Base class for Laravel migrations.

2. Migration Class:

   • Extends Migration to create a migration file.
   • Class name should reflect the purpose (e.g., AddVirtualColumnToProductsTable).

3. up Method:

   • Contains the code executed during migration (adding virtual columns).
   • Uses Schema::table to modify the existing products table.

4. Virtual Column Definition:

5. down Method (Optional):

   • Contains code for rollback (removing virtual columns).
   • Uses $table->dropVirtual to remove both total_price and discounted_price (if added).

Remember:

• Replace products with your actual table name.
• Adjust column names (quantity, unit_price, and discount) if they differ in your table.
• Execute php artisan migrate to apply the migration and add the virtual columns.
• To remove the virtual columns later, run php artisan migrate:rollback.

This approach defines an accessor method within your Eloquent model to calculate the virtual column's value dynamically. It's useful when the calculation is specific to your model logic or involves additional data not stored in the database.

class Product extends Model
{
    public function getTotalPriceAttribute()
    {
        return $this->quantity * $this->unit_price;
    }
}

Access:

$product = Product::find(1);
echo $product->total_price; // Calls the accessor method

Global Scopes:

Global scopes allow you to modify queries across your model throughout the application. You can use a global scope to automatically add the virtual column selection to all queries. This is convenient for frequently used virtual columns.

class Product extends Model
{
    protected static function boot()
    {
        parent::boot();

        static::addGlobalScope('addTotalPrice', function (Builder $builder) {
            $builder->addSelect(DB::raw('quantity * unit_price AS total_price'));
        });
    }
}

$product = Product::find(1);
echo $product->total_price; // Automatically included in the query

MySQL Views:

If you have complex calculations involving multiple joins or data from other tables, creating a MySQL view can be an efficient alternative. This approach encapsulates the logic outside your Laravel application.

Example (assuming a discounts table):

CREATE VIEW product_details AS
SELECT p.*,
       p.quantity * p.unit_price * (1 - d.discount / 100) AS discounted_price
FROM products p
LEFT JOIN discounts d ON p.product_id = d.product_id;

Model for the View:

class ProductDetails extends Model
{
    protected $table = 'product_details';

    public $timestamps = false; // Disable timestamps as the view doesn't manage them
}

$product = ProductDetails::find(1);
echo $product->discounted_price; // Fetches data from the view

Choosing the Right Method:

• virtualAs: Suitable for simple calculations based on existing columns in same table.
• Accessor Methods: Good for model-specific calculations or involving non-database data.
• Global Scopes: Convenient for frequently used virtual columns across the model.
• MySQL Views: Ideal for complex calculations or data from other tables.