Fatal error cannot use because the name is already in use

This is an error happened upon executing a command for processing migration script file. The concept itself, the migration script file processing is a concept or not only just a concept but also the implementation offered in Laravel web-based application development to operate with tables represented by each of the migration script file. The file itself is not specified since the process of executing the migration script files are done by executing all of the migration script files located normally in folder ‘/database/migrations’.

All of the migration script files can be executed by typing the following command in the bash prompt :

php artisan migrate:refresh

Below is the output of the above command execution :

user@hostname:/var/www/html/laravel$ php artisan migrate:refresh
PHP Fatal error: Cannot declare class CreateCategoriesTable, because the name is already in use in /var/www/html/laravel-support-ticket/database/migrations/2017_11_02_151257_create_categories_table.php on line 31

[SymfonyComponentDebugExceptionFatalErrorException]
Cannot declare class CreateCategoriesTable, because the name is already in use

user@hostname:/var/www/html/laravel$

In this article context, especially based on the above output generated by executing the commad php artisan migrate:refresh, the process cannot be proceed since it is actually generated an error message as shown in the above output. The error message is actually : “Cannot declare class CreateCategoriesTable, because the name is already in use”.

In the above context, “CreateCategoriesTable” is actually the name of the class specified in the migartion script file. It said that the class name has already exist because in the term of this case, there are three files which has the same name part which in the end there are three migration script files which have the same class name. Although those files are generated in the different time but it actually refers to the same class name. The situation is shown in the following :

user@hostname:/var/www/html/laravel/database/migrations$ ls -al
total 16
drwxrwxr-x 2 user     user 4096 Nov 5 22:08 .
drwxrwxr-x 3 www-data user 4096 Nov 5 22:22 ..
...
-rw-rw-r-- 1 www-data user 601 Nov 2 22:06 2017_11_02_150646_create_categories_table.php
-rw-rw-r-- 1 www-data user 601 Nov 2 22:12 2017_11_02_151257_create_categories_table.php
-rw-rw-r-- 1 www-data user 601 Nov 2 22:19 2017_11_02_151921_create_categories_table.php
...
user@hostname:/var/www/html/laravel/database/migrations$

In the context of this article, the solution which I implemented to solve the problem is by moving away the other files unnecessary. Since it can only be one script representing one class, just move the rest of the files into another location. I created one folder in the current path shown above and move the other two older files inside the folder. It is shown as follows :

user@hostname:/var/www/html/laravel/database/migrations$ mkdir temp
user@hostname:/var/www/html/laravel/database/migrations$

And move those files unrelated :

user@hostname:/var/www/html/laravel/database/migrations$ mv 2017_11_02_150646_create_categories_table.php 2017_11_02_151257_create_categories_table.php temp/
user@hostname:/var/www/html/laravel/database/migrations$ cd temp
user@hostname:/var/www/html/laravel/database/migrations$ ls -al 
total 16
drwxrwxr-x 2 user     user 4096 Nov 5 22:08 .
drwxrwxr-x 3 www-data user 4096 Nov 5 22:22 ..
-rw-rw-r-- 1 www-data user  601 Nov 2 22:06 2017_11_02_150646_create_categories_table.php
-rw-rw-r-- 1 www-data user  601 Nov 2 22:12 2017_11_02_151257_create_categories_table.php
user@hostname:/var/www/html/laravel/database/migrations/temp#

Summary: in this tutorial, you’ll learn about PHP namespaces, how to define classes that belong to a namespace, and how to use namespaces.

Why namespaces

When your project grows in complexity, you’ll need to integrate the code from others. Sooner or later, you’ll find that your code has different classes with the same name. This problem is known as name collision.

To resolve it, you can use namespaces. PHP supported namespaces since version 5.3.

What is a namespace

It’s easier to understand namespaces by analogy to the directory structure in a filesystem.

A directory stores related files, which is similar to a namespace that groups related classes.

A directory doesn’t allow you to have two files with the same name. However, you can have files with the same names in different directories. Likewise, namespaces mimic the same principle.

By definition, namespaces provide you with a way to group related classes and help you avoid any potential name collisions.

Namespaces are not limited to group classes. They can group other identifiers, including functions, constants, variables, etc.

Set up a directory structure

First, create a project directory, e.g., store and create a new index.php file in the directory.

Second, create src directory in the project directory and Model directory in the src directory.

Third, create a new file called Customer.php in the Model directory with the following code:

<?php

class Customer
{
    private $name;

    public function __construct($name)
    {
        $this->name = $name;
    }

    public function getName()
    {
        return $this->name;
    }
}
Code language: HTML, XML (xml)

The directory looks like the following:

.
├── index.php
└── src
    └── Model
        └── Customer.php
Code language: plaintext (plaintext)

Define a namespace

To define a namespace, you place the namespace keyword followed by a name at the very top of the page. The following example gives the Customer class with a namespace StoreModel:

<?php

namespace StoreModel;

class Customer
{
    private $name;

    public function __construct($name)
    {
        $this->name = $name;
    }

    public function getName()
    {
        return $this->name;
    }
}
Code language: HTML, XML (xml)

• It’s customary to assign the src directory the Store namespace. And you can replace Store with your brand name, e.g., Apple.
• It’s a good practice to imitate the directory structure with the namespace to find classes more easily. For example, every class within the directory will get the namespace StoreModel.

Use a class that belongs to a namespace

To use a class that belongs to a namespace in the index.php, you need to include the file and use the class:

<?php

require 'src/Model/Customer.php';

$customer = new Customer('Bob');
echo $customer->getName();
Code language: HTML, XML (xml)

If you open the index.php, you’ll get a fatal error:

Fatal error: Uncaught Error: Class 'Customer' not found in...
Code language: JavaScript (javascript)

Since the Customer class now is namespaced, you need to use the fully qualified name that includes the namespace like this:

<?php

require 'src/Model/Customer.php';

$customer = new StoreModelCustomer('Bob');
echo $customer->getName();
Code language: HTML, XML (xml)

Now, it should work properly.

Import a namespace

To avoid using the fully qualified names from a namespace, you can import the namespace with the use operator like this:

<?php

require 'src/Model/Customer.php';
use StoreModel;

$customer = new ModelCustomer('Bob');
echo $customer->getName();
Code language: HTML, XML (xml)

Now, you just need to prefix the class name with Model.

Import a class from a namespace

PHP allows you to import a class from a namespace instead of importing the namespace. For example:

<?php

require 'src/Model/Customer.php';
use StoreModelCustomer;

$customer = new Customer('Bob');
echo $customer->getName();
Code language: HTML, XML (xml)

In this example, we use the use operator to import the Customer class from the StoreModel namespace. Therefore, we don’t have to prefix the class name with the namespace.

Import multiple classes from a namespace

First, create a new file called Product.php in the src/Model directory:

<?php

namespace StoreModel;

class Product
{
}
Code language: HTML, XML (xml)

For demonstration purposes, the Product class is empty. Now, the directory structure looks like the following:

.
├── index.php
└── src
    └── Model
        ├── Customer.php
        └── Product.php
Code language: plaintext (plaintext)

To use both Customer and Product classes from the index.php, you can import them individually like before:

<?php

require 'src/Model/Customer.php';
require 'src/Model/Product.php';

use StoreModelCustomer;
use StoreModelProduct;

$customer = new Customer('Bob');
echo $customer->getName();

$product = new Product();
Code language: HTML, XML (xml)

When the number of imported classes grows, your code will become more verbose. So instead of importing each individual class, you can import all the classes using a single statement:

use namespace{className1, className2, ...}
Code language: PHP (php)

For example:

<?php

require 'src/Model/Customer.php';
require 'src/Model/Product.php';

use StoreModel{Customer, Product};

$customer = new Customer('Bob');

echo $customer->getName();

$product = new Product();
Code language: HTML, XML (xml)

Alias classes from a namespace

First, create a new directory called Database under the project directory and place a new file Logger.php in the Database directory with the following code:

<?php

namespace StoreDatabase;

class Logger
{
    public function log($message)
    {
        var_dump('Log ' . $message . ' to the database.');
    }
}
Code language: HTML, XML (xml)

Second, create a new directory Utils under the project directory and create a new Logger.php in the Utils directory.

<?php

namespace StoreUtils;

class Logger
{
    public function log($message)
    {
        var_dump('Log ' . $message);
    }
}
Code language: HTML, XML (xml)

Now, you have two classes with the same name in different namespaces:

.
├── index.php
└── src
    ├── Database
    │   └── Logger.php
    ├── Model
    │   ├── Customer.php
    │   └── Product.php
    └── Utils
        └── Logger.php
Code language: plaintext (plaintext)

Third, import Logger classes from both namespaces StoreUtils and DatabaseLogger into the index.php file:

<?php

require 'src/Utils/Logger.php';
require 'src/Database/Logger.php';

use StoreUtilsLogger;
use StoreDatabaseLogger;
Code language: HTML, XML (xml)

PHP raises the following error:

Fatal error: Cannot use StoreDatabaseLogger as Logger because the name is already in use in...
Code language: plaintext (plaintext)

To avoid this, you can just import the namespaces:

<?php

require 'src/Utils/Logger.php';
require 'src/Database/Logger.php';

use StoreUtils;
use StoreDatabase;

$loggers = [
    new UtilsLogger(),
    new DatabaseLogger()
];
Code language: HTML, XML (xml)

Or you can give a class an alias when importing it:

import namespaceclassName as newClassName;
Code language: JavaScript (javascript)

The following example assigns the DatabaseLogger class an alias to the StoreDatabaseLogger class:

<?php

require 'src/Utils/Logger.php';
require 'src/Database/Logger.php';

use StoreUtilsLogger;
use StoreDatabaseLogger as DatabaseLogger;

$loggers = [
    new Logger(),
    new DatabaseLogger()
];
Code language: HTML, XML (xml)

Use classes from the global namespace

To use global classes such as built-in classes or user-defined classes without a namespace, you need to precede the name of such classes with a backslash ().

The following example shows how to use the built-in DateTime class in the App namespace:

<?php

namespace App;

$publish_at = new DateTime();

echo $publish_at->format('Y-m-d H:i:s');
Code language: HTML, XML (xml)

Summary

• Use a namespace to group related classes.
• Mimic the directory structure with the namespaces to make it easier to find the classes.
• Use the use operator to import a namespace or a class from a namespace.
• Use the as keyword to assign a namespace or a class of a namespace an alias.