DML 操作で同時に使用できない sObject

1public class MixedDMLFuture {
2    public static void useFutureMethod() {
3        // First DML operation
4        Account a = new Account(Name='Acme');
5        insert a;
6        
7        // This next operation (insert a user with a role) 
8        // can't be mixed with the previous insert unless 
9        // it is within a future method. 
10        // Call future method to insert a user with a role.
11        Util.insertUserWithRole(
12            'mruiz@awcomputing.com', 'mruiz', 
13            'mruiz@awcomputing.com', 'Ruiz');        
14    }
15}

1public class Util {
2    @future
3    public static void insertUserWithRole(
4        String uname, String al, String em, String lname) {
5
6        Profile p = [SELECT Id FROM Profile WHERE Name='Standard User'];
7        UserRole r = [SELECT Id FROM UserRole WHERE Name='COO'];
8        // Create new user with a non-null user role ID 
9        User u = new User(alias = al, email=em, 
10            emailencodingkey='UTF-8', lastname=lname, 
11            languagelocalekey='en_US', 
12            localesidkey='en_US', profileid = p.Id, userroleid = r.Id,
13            timezonesidkey='America/Los_Angeles', 
14            username=uname);
15        insert u;
16    }
17}