Updating a Postgres Enum Column with a Laravel Migration

The enumerated data type (enum) provides a convenient way to constraint a column to a set of values. However, the implementation of enum in Laravel is not as it seems, and changing the set of values can prove difficult later on. This post looks at how Laravel sets a column to enum in the database and provides details on how to change the available set of values using a migration script.

Laravel Enum

As already mentioned, when a column is set to enum in a migration script, the resulting data type in the database for that column is different. Below shows an example of a migration script setting a column to enum and the resulting data type in the database.

public function up()
{
    Schema::create('messages', function (Blueprint $table) {
        ...
        $table->enum('status', ['draft', 'sent', 'read']);
        ...
    });
}

Column     |              Type              | Collation | Nullable | Default                 
-----------+--------------------------------+-----------+----------+-----------------------------------------
...
status     | character varying(255)         |           | not null  |
...

As can be seen in the data description above, the data type set for the status column in the database is character varying(255). This can be seen in the source code of Laravel.

Therefore, to limit the column to only the set of values provided, a constraint is added to the column, as shown below.

Check constraints:
    "messages_status_check" CHECK (status::text = ANY (ARRAY['draft'::character varying, 'sent'::character varying, 'read'::character varying]::text[]))

Updating an Enum

Looking at the Laravel documentation, it states that updating a column with type enum is not supported when using the Doctrine DBAL library. However, since we know about the actual implementation of an enum column, discussed above, we can look for a method of updating such a column.

An approach that can be taken to altering the constraint is shown below. First, the constraint is dropped. Second, the new constraint is generated as a string. Finally, the new constraint is applied to the messages table.

<?php

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

class ChangeEnum extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        DB::statement("ALTER TABLE messages DROP CONSTRAINT messages_status_check");

        $types = ['draft', 'sent', 'read', 'replied'];
        $result = join( ', ', array_map(function ($value){
            return sprintf("'%s'::character varying", $value);
        }, $types));

        DB::statement("ALTER TABLE messages ADD CONSTRAINT messages_status_check CHECK (status::text = ANY (ARRAY[$result]::text[]))");
    }

    /**
     * Reverse the migrations.
     *
     * @return void
     */
    public function down()
    {
        //
    }
}

View this code as a GitHub Gist.

Summary

To summarise, this post investigated the enum data type used by Laravel. First, an example of how a column can be set to the type enum using a migration script is shown. Second, the actual implementation of the enum type in the database was revealed. Finally, an example of how to update a column that has been set to enum was presented, as it is not currently supported by the Doctrine DBAL library.