一个简单的应用(用内置数据库)
领域类：
1.Race.groovy

package com.rt

class Race {
	
	String name
	Date startDate
	String city
	String state
	BigDecimal distance
	BigDecimal cost
	Integer maxRunners=100000
	
	static hasMany=[registrations:Registration]

    static constraints = {
		name(blank:false,maxSize:50)
		startDate(validator:{return(it>new Date())})
		city()
		state(inList:["GA","NC","SC","VA"])
		distance(min:0.0)
		cost(min:0.0,max:100.0)
		maxRunners(min:0,max:1000000)
    }
	
	BigDecimal inMiles(){
		return distance*0.6214
	}
	
	@Override
	public String toString() {
		return "${name},${startDate.format('yyyy/MM/dd')}"
	}
}

2.Registration.groovy

package com.rt

class Registration {
	
	Boolean paid
	Date dateCreated
	
	static belongsTo =	[race:Race,runner:Runner]
	
	static constraints = {
		race()
		runner()
		paid()
		dateCreated()
	}
	
	@Override
	public String toString() {
		return "${race}:${runner}"
	}
}

3.Runner.groovy

package com.rt

import java.util.Date;

class Runner {

	String firstName
	String lastName
	Date dateOfBirth
	String gender
	String address
	String city
	String state
	String zipcode
	String email
	
	static hasMany=[registrations:Registration]

    static constraints = {
		firstName(blank:false)
		lastName(blank:false)
		dateOfBirth()
		gender(inList:['男','女'])
		address()
		city()
		state()
		zipcode()
		email(email:true)
    }
	
	@Override
	public String toString() {
		return "${firstName},${lastName}(${email}"
	}
}

控制器：
1.RaceController.groovy

package com.rt

class RaceController {

	def scaffold=Race
	
//    def index = { 
//		render "hello world"
//	}
}

2.RegistrationController.groovy

package com.rt

class RegistrationController {

	def scaffold=true
	
//    def index = { }
}

3.RunnerController.groovy

package com.rt

class RunnerController {

	def scaffold=true
}

因为是内置数据库，所以每次重启服务器时，数据就丢失，这是grails内部机制，可以用以下办法在每次服务器启动时保存初始数据到内置数据库：
在grails-app/conf/BootStrap.groovy

import com.rt.Race 
import com.rt.Registration 
import com.rt.Runner 
import grails.util.GrailsUtil;

class BootStrap {

    def init = { servletContext ->
		switch(GrailsUtil.environment){
			case "development":
			def jane=new Runner(
				firstName:'三',
				lastName:'张',
				dateOfBirth:(new Date()-365*30),
				gender:'男',
				address:'地址',
				city:'hz',
				state:'NC',
				zipcode:'123456',
				email:'jane@163.com'
				)
				jane.save()
				jane.errors.each {
					println it
				}
				
				def trot=new Race(
					name:'500长跑',
					startDate:(new Date()+90),
					city:'HZ',
					state:'NC',
					distance:500,
					cost:20.0,
					maxRunners:350
				)
				trot.save()
				if(trot.hasErrors()){
					println trot.errors
				}
				
				def reg=new Registration(
					paid:false,
					runner:jane,
					race:trot
				)
				reg.save()
				reg.errors.each { 
					println it
				}
			break
		}
    }
    def destroy = {
    }
}