laravel/framework · error · LogicException

This database driver does not support modifying generated…

Error message

This database driver does not support modifying generated columns.

What it means

PostgresGrammar::modifyVirtualAs throws a LogicException when a column is being modified ($column->change is true) AND a non-null virtualAs attribute is present. PostgreSQL cannot ALTER a generated VIRTUAL expression in place; you must drop and recreate the column. Setting virtualAs back to null is allowed (it emits 'drop expression if exists'), but providing a new expression on a change is not.

Solutions

Drop the virtualAs attribute when calling ->change() for unrelated modifications: $table->integer('col')->change() without virtualAs.
To change the expression, split into two migrations: drop the column (or drop expression), then re-add it with the new virtualAs.
If the intent was to remove the generation expression, call ->virtualAs(null)->change() which emits 'drop expression if exists'.

Example fix

// before
$table->integer('total')->virtualAs('a + b')->change();

// after (replace the expression)
// migration 1
Schema::table('orders', fn (Blueprint $t) => $t->dropColumn('total'));
// migration 2
Schema::table('orders', fn (Blueprint $t) => $t->integer('total')->virtualAs('a + b + fee'));

Defensive patterns

Strategy: validation

Validate before calling

// when modifying a column on Postgres, do NOT resend virtualAs unless you mean to drop it
$col = $table->integer('total');
if (! $columnWantsNewExpression) {
    // just change another attribute
    $col->nullable(false)->change();
} else {
    // to remove the expression:
    $col->virtualAs(null)->change();
}

Prevention

Split generated-column expression changes into drop + re-add migrations on Postgres.
When calling ->change(), only set the attributes you intend to alter.
Use ->virtualAs(null)->change() to drop an expression, never a new expression.

When it happens

Trigger: Using $table->integer('col')->virtualAs('expr')->change() (i.e. a column modification that supplies a non-null virtualAs) on a Postgres connection.

Common situations: Calling ->change() on a migration that also redefines the generation expression; trying to repoint a generated column at a new formula in a Postgres-only deploy; migration scaffolding tools that always resend all attributes on change.

Related errors

AI-assisted analysis of laravel/framework@e0f6eb3518 (2026-08-11). Data as JSON: /api/errors/58de220de6e5dbee. Report an issue: GitHub.

Appendix: source

Thrown at src/Illuminate/Database/Schema/Grammars/PostgresGrammar.php:1283

        }
    }

    /**
     * Get the SQL for a generated virtual column modifier.
     *
     * @param  \Illuminate\Database\Schema\Blueprint  $blueprint
     * @param  \Illuminate\Support\Fluent  $column
     * @return string|null
     *
     * @throws \LogicException
     */
    protected function modifyVirtualAs(Blueprint $blueprint, Fluent $column)
    {
        if ($column->change) {
            if (array_key_exists('virtualAs', $column->getAttributes())) {
                return is_null($column->virtualAs)
                    ? 'drop expression if exists'
                    : throw new LogicException('This database driver does not support modifying generated columns.');
            }

            return null;
        }

        if (! is_null($column->virtualAs)) {
            return " generated always as ({$this->getValue($column->virtualAs)}) virtual";
        }
    }

    /**
     * Get the SQL for a generated stored column modifier.
     *
     * @param  \Illuminate\Database\Schema\Blueprint  $blueprint
     * @param  \Illuminate\Support\Fluent  $column
     * @return string|null
     *
     * @throws \LogicException

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