laravel/framework · error · LogicException

This database driver does not support modifying generated co

Error message

This database driver does not support modifying generated columns.

What it means

PostgreSQL cannot ALTER a generated virtual column to a new expression; it can only drop the expression. modifyVirtualAs() throws LogicException specifically when a change-modify operation ($column->change === true) supplies a non-null virtualAs value. Passing virtualAs(null) is allowed and emits 'drop expression if exists'.

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

View on GitHub (pinned to bd6b5437e6)

Solutions

Drop the existing generated column and recreate it with the new expression instead of using change().
If you only want to remove the expression, call ->virtualAs(null)->change() which emits 'drop expression if exists'.
Move the expression into a view or a generated-as-identity approach if frequent changes are expected.
Confirm the target driver: this works on MySQL but not Postgres — split driver-specific migrations.

Example fix

// before (throws on Postgres)
Schema::table('orders', function (Blueprint $table) {
    $table->integer('total')->virtualAs('price * qty')->change();
});

// after (drop then recreate)
Schema::table('orders', function (Blueprint $table) {
    $table->integer('total')->virtualAs(null)->change(); // drop expression
});
Schema::table('orders', function (Blueprint $table) {
    $table->integer('total')
          ->virtualAs('price * qty + tax')
          ->change();
});
// cleanest: dropColumn + add the column fresh

Defensive patterns

Strategy: validation

Validate before calling

// On Postgres, never change() a non-null virtualAs
if (Schema::getConnection()->getDriverName() === 'pgsql') {
    // drop the column and re-add it instead of ->change()
}

Prevention

Postgres cannot modify generated expressions — only drop them via ->virtualAs(null)->change().
For formula changes, dropColumn then re-add the generated column.
Driver-split migrations that change generated columns.

When it happens

Trigger: Using $table->string('col')->virtualAs('new_expr')->change() in a Postgres migration — i.e. trying to update an existing generated column's expression via the change() modifier. The same call with virtualAs(null)->change() succeeds (drops the expression).

Common situations: Refactoring a generated column's formula in Postgres; running a migration that worked on MySQL (which permits modifying generated columns) against a Postgres database; auto-sync tools that diff columns and try to change the expression.

Related errors

AI-assisted analysis of laravel/framework@bd6b5437e6 (2026-08-06). Data as JSON: /data/errors/58de220de6e5dbee.json. Report an issue: GitHub.