我正在进行结帐，当用户去购物时，会创建一个Purchase对象并将其保存到数据库中。然后，我获取对象的id并将其发送给PayPal以生成一个按钮(这样以后我就可以识别购买了)。但是，当我尝试检索id时，它返回null。

在访问ID之前，我尝试过刷新它，但是它似乎仍然无法正常工作。

这是我的域对象:

package website

import java.time.Instant
import java.time.temporal.ChronoUnit

class Purchase {
    String buttonId
    final Instant expires
    private boolean complete

    User user
    Product product

    Purchase(Product product, User user) {
        this.product = product
        this.user = user

        expires = Instant.now().plus(1, ChronoUnit.DAYS)
    }

    void completePurchase() {
        // confirm that the purchase hasn't been completed already
        if (complete) {
            throw new PurchaseAlreadyCompleteException()
        }

        complete = true
    }

    boolean isComplete() {
        return complete
    }

    static class ButtonIdAlreadyInitializedException extends RuntimeException {}

    static class PurchaseAlreadyCompleteException extends RuntimeException {}
}

Purchase purchase = new Purchase(product, user)
purchase.save(flush: true)
println 'purchase id: ' + purchase.id

最佳答案

该ID为null，因为未保存您的对象。之所以不被保存，是因为您没有为buttonId分配值，并且此属性是必需的。您可以使用以下方法进行验证:

Purchase purchase = new Purchase(product, user)
purchase.save(flush: true, failOnError: true) // will throw an exception if saving fails
println 'purchase id: ' + purchase.id

https://stackoverflow.com/questions/39215071/