class Song {
    String title
    String artist
    Integer duration
    static constraints = {
        title(blank: false)
        artist(blank: false)
        duration(min: 1)
    }
}

// -68 是一个无效的值
def song = new Song(title:'The Rover',
                    artist:'Led Zeppelin',
                    duration:-68)
if(song.save()) {
    println "Song was created!"
} else {
    song.errors.allErrors.each { println it.defaultMessage }
}

package org.springframework.validation
interface Errors {
    List getAllErrors();
    int getErrorCount();
    FieldError getFieldError(String feldName);
    int getFieldErrorCount();
    List getFieldErrors(String feldName);
    Object getObjectName();
    boolean hasErrors();
    boolean hasFieldErrors(String feldName);
    // ... remaining methods
}

def song = new Song(title:'The Rover',
                    duration:339)
if(!song.validate()) {
    song.clearErrors()
    song.artist = 'Led Zeppelin'
    song.validate()
}

class User {
    static constraints = {
        password(unique:true, length:5..15, validator:{val, obj ->
            if(val?.equalsIgnoreCase(obj.frstName)) {
                return false
            }
        })
    }