# Laravel Migrations

• Quick Reference
• Foreign Key Constraints
• Cascade Actions
• Check for Table Existence

# Quick Reference

# Foreign Key Constraints

Laravel Foreign Key Constraints

When using the verbose syntax, you must define the column before defining the foreign key constraint.

// verbose syntax
$table->unsignedBigInteger('user_id');
$table->foreign('user_id')->references('id')->on('users');

// terser syntax automatically creates an UNSIGNED BIGINT equivalent column
$table->foreignId('user_id')->constrained();

To force referential integrity, you can add the ->constrained() method to the column definition. This will create a foreign key constraint on the column.

$table->foreignId('user_id')->constrained();

# Cascade Actions

$table->foreignId('post_id')->constrained()->cascadeOnDelete();

$table->cascadeOnUpdate();      // Updates should cascade.
$table->restrictOnUpdate();     // Updates should be restricted.
$table->cascadeOnDelete();      // Deletes should cascade.
$table->restrictOnDelete();     // Deletes should be restricted.
$table->nullOnDelete();         // Deletes should set the foreign key value to null.

# Check for Table Existence

if (!Schema::hasTable('table_name')) {
    // Do stuff
}