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I will explain about Laravel collections. For beginners, I think you might be wondering "What even is a collection?", so I hope this explanation helps.

The content of this article is based on excerpts from Laravel official documentation.

What is a Collection?

Roughly speaking, it's like an array.

Intuitively, it can be divided into the following categories:

① What you get when you use get() or all() methods for data retrieval

② Things you generate using collect yourself

① Creating a Collection with a Simple Array

When no key is specified, it will be displayed in the following format.

$array = [1,2,3,4,5];
$collection1 = collect($array);
dd($collection1);

Illuminate\Support\Collection {#338 ▼
  #items: array:5 [▼
    0 => 1
    1 => 2
    2 => 3
    3 => 4
    4 => 5
  ]
}

If you specify the array index, you can retrieve only that element.

dd($collection1[0]);
// Outputs 1

② Creating a Collection with a key

Unlike before, you will use a key.

$array2 = [
    [
        'user_id'=> 1,
        'name' => 'Sato',
    ],
    [
        'user_id'=> 2,
        'name' => 'Takeru',
    ],
    [
        'user_id'=> 3,
        'name' => 'Shun',
    ],
    [
        'user_id'=> 4,
        'name' => 'Oguri',
    ],
];
$collection2 = collect($array2);
dd($collection2);

Output

Illuminate\Support\Collection {#350 ▼
#items: array:4 [▼
0 => array:2 [▼
"user_id" => 1
"name" => "Sato"
]
1 => array:2 [▼
"user_id" => 2
"name" => "Takeru"
]
2 => array:2 [▼
"user_id" => 3
"name" => "Shun"
]
3 => array:2 [▼
"user_id" => 4
"name" => "Oguri"
]
]
}

Specify the order just like with arrays.

dd($collection2[0]);

Output

// Only the first data is retrieved.
array:2 [▼
  "user_id" => 1
  "name" => "Sato"
]

To retrieve a specific key

dd($collection2[0]['user_id']);

Output

// Only the user_id of the first element is retrieved
1

Benefits

It's easy to manipulate data, such as searching or changing the order.

Example

I think I created an example using key earlier,

Let's say we want to retrieve the data where user_id is 1.

//You can search by key using where
dd($collection2->where('user_id',1));

Output

// Retrieved the data where user_id is 1.
// If there are multiple data with user_id 1, they will all be retrieved. Therefore, the retrieved data is a collection.
Illuminate\Support\Collection {#353 ▼
  #items: array:1 [▼
    0 => array:2 [▼
      "user_id" => 1
      "name" => "Sato"
    ]
  ]
}

These searching methods like where are quite similar to the ones used in Eloquent when retrieving data from a database (like where and orderBy), so they are easy to understand.

Are Collections used when retrieving data from a database?

A. Collections are used for retrieving multiple items.

(Single item retrieval results in an object)

In other words,

Post::get();
Post::all();

will retrieve multiple items as a Collection.

A. Single item retrieval results in an object.

Post::first();
Post::find(1);

will retrieve a single item as an object.

Summary

That's all.

Personally, I thought it might be easier to understand if I explained what a collection is by showing examples rather than explaining in words, so I wrote this.

I would be glad if it was helpful to someone!

If you have any comments or feedback, please contact me via DM on Twitter.

That's all!

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