how to set foreign key in laravel migration code example

Example 1: laravel foreign key

Schema::table('posts', function (Blueprint $table) {
    $table->unsignedBigInteger('user_id');

    $table->foreign('user_id')->references('id')->on('users');
});
OR
Schema::table('posts', function (Blueprint $table) {
    $table->foreignId('user_id')->constrained();
});

Example 2: laravel migration foreign key 5.6

Schema::table('posts', function (Blueprint $table) {
    $table->unsignedInteger('user_id');

    $table->foreign('user_id')->references('id')->on('users');
});

Example 3: laravel migration constrained

Schema::table('posts', function (Blueprint $table) {
    $table->foreignId('user_id')->constrained();
});

/* The foreignId method is an alias for unsignedBigInteger while the
 * constrained method will use conventions to determine the table and
 * column name being referenced. If your table name does not match
 * Laravel's conventions, you may specify the table name by passing it
 * as an argument to the constrained method:
*/

Schema::table('posts', function (Blueprint $table) {
    $table->foreignId('user_id')->constrained('users');
});