Why is my model's primary key zero after saving?

When the database and Eloquent disagree

Joel Clermont

2026-10-08

I had a model where the primary key was user_id instead of id. It was a one-to-one profile table, so the user's ID made a natural key.

class Profile extends Model
{
    protected $primaryKey = 'user_id';

    protected $fillable = ['user_id', 'bio'];
}

After I created a record, something strange happened.

$profile = Profile::create([
    'user_id' => 42,
    'bio' => 'Hello world',
]);

$profile->user_id; // 0

The database had 42, exactly as expected. But the model in memory said 0, and nothing threw an error.

By default, Eloquent assumes the primary key is an auto-incrementing integer. So after the insert, it asks the database for the last inserted ID and writes that value back to the key on the model. That's how a brand new model gets its id without another query.

In this case, the column wasn't auto-incrementing, so MySQL had no generated ID to report. It returned 0, and Eloquent overwrote my 42 with it.

The fix is to tell Eloquent the key isn't auto-incrementing:

class Profile extends Model
{
    protected $primaryKey = 'user_id';

    public $incrementing = false;

    protected $fillable = ['user_id', 'bio'];
}

Now Eloquent skips that step and keeps the value I passed in.

Here to help,

Joel

P.S. Catching a missing $incrementing before it turns into a confusing bug is exactly the kind of thing we look for in a code review.

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