怎么避免多个 session 同时操作 Collection ？？？

写了一个简单的点评网站抓取的程序

今天后台碰到了：

ERROR org.grails.web.errors.GrailsExceptionResolver - HibernateException occurred when processing request: [POST] /cities/yelp/94349
llegal attempt to associate a collection with two open sessions. Collection : [com.ttt.website.backend.domains.BeautySpots.beautySpotsImages#dianping-48232229]. Sta
ktrace follows:
rg.springframework.orm.hibernate4.HibernateSystemException: Illegal attempt to associate a collection with two open sessions. Collection : [com.ttt.website.backend.
omains.BeautySpots.beautySpotsImages#dianping-48232229]; nested exception is org.hibernate.HibernateException: Illegal attempt to associate a collection with two open se

1. Collection : [com.ttt.website.backend.domains.BeautySpots.beautySpotsImages#dianping-48232229]
   at com.ttt.website.backend.tools.dianping.DianPingRestaurantsScraper$_saveRestaurants_closure1.doCall(DianPingRestaurantsScraper.groovy:135)
   at grails.gorm.transactions.GrailsTransactionTemplate$2.doInTransaction(GrailsTransactionTemplate.groovy:90)
   at grails.gorm.transactions.GrailsTransactionTemplate.execute(GrailsTransactionTemplate.groovy:87)
   at com.ttt.website.backend.tools.dianping.DianPingRestaurantsScraper.saveRestaurants(DianPingRestaurantsScraper.groovy:133)
   at com.ttt.website.backend.tools.dianping.DianPingRestaurantsScraper.scrape(DianPingRestaurantsScraper.groovy:41)
   at com.ttt.website.backend.controllers.CitiesController.$tt__yelp(CitiesController.groovy:388)
   at grails.transaction.GrailsTransactionTemplate$2.doInTransaction(GrailsTransactionTemplate.groovy:96)
   at grails.transaction.GrailsTransactionTemplate.execute(GrailsTransactionTemplate.groovy:93)
2. by: org.hibernate.HibernateException: Illegal attempt to associate a collection with two open sessions. Collection : [com.ttt.website.backend.domains.BeautySp

ts.beautySpotsImages#dianping-48232229]

   ... 8 common frames omitted

有一个类：BeautySpots，它是表示每一个餐馆，在这个类里面，引用了另外一个表：
beautySpotsImages

这个是保存的餐馆的图片

异常就是说有两个 session 在同时访问这个 Collection

这个程序是单线程跑的

我贴一下代码（Groovy的代码）

?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
restaurant.description = description.toString()

BeautySpots.withTransaction([propagationBehavior: TransactionDefinition.PROPAGATION_REQUIRES_NEW,

 isolationLevel: TransactionDefinition.ISOLATION_READ_COMMITTED]) {
restaurant.save(failOnError: true, flush: true) //这里出的问题

}

savedRestaurantsAmount++

if (isNewRestaurant) {

imageUrls = getImageUrls(restaurant.referTo, shopId)
// 下载图片在下面的方法： ScraperUtil.saveRestaurantImages

if (!ScraperUtil.saveRestaurantImages(restaurant, creator, restaurant.referTo, imageUrls, 0, 70)) {

    restaurant.delete()
    return
}

}
restaurant.completionProgress = POIUtil.getCompletionProgress(restaurant)
BeautySpots.withTransaction([propagationBehavior: TransactionDefinition.PROPAGATION_REQUIRES_NEW,

 isolationLevel: TransactionDefinition.ISOLATION_READ_COMMITTED]) {
restaurant.save(failOnError: true)

}