grails - 为什么Grails似乎正在保存无效的域对象？

Question

我正在使用Grails 2.4.2。我正在保存违反约束的域类的实例，因此我希望保存会失败。但它似乎成功了。 Grails文档指出:

Another thing to bear in mind is that Grails validates a domain instance every time you save it. If that validation fails the domain instance will not be persisted to the database.

域类:

class Book {
    String name
    static constraints = {
        name unique: true
    }
    String toString() { "[Book: id=${id} name=${name}]" }
}

以下代码修改了第二个实例，使其与第一个实例具有相同的名称，并尝试保存它(book3.save)。我希望这会失败，并且确实会返回null。但是随后我通过ID(Book.get(book2.id))加载了同一对象，并发现它具有新名称。最后，它会打印整个书籍 list ，我们看到它们都具有相同的名称。

    def book1 = new Book(name: "Cats").save()
    def book2 = new Book(name: "Dogs").save()
    log.info "The books: ${Book.list()}"
    def book3 = Book.get(book2.id)
    book3.name = "Cats"
    def book3save = book3.save() // Should fail?
    def book4 = Book.get(book2.id)
    log.info "The result of saving book ${book2.id} with name 'Cats' is ${book3save}"
    log.info "The book with ID ${book2.id} is now named ${book4.name}"
    log.info "The books are: ${Book.list()}"

输出:

The books: [[Book: id=1 name=Cats], [Book: id=2 name=Dogs]]
The result of saving book 2 with name 'Cats' is null
The book with ID 2 is now named Cats
The books are: [[Book: id=1 name=Cats], [Book: id=2 name=Cats]]

Answer 1

默认情况下，Grails不会在验证错误上引发异常。你可以做

book3.save(failOnError: true)

这将引发异常。

或者您需要检查save()的返回值。 null表示验证失败。您也可以执行book3.validate()来查看实例是否有效，然后再尝试保存。

我认为您在正在更新的书的外观中看到的是由于休眠 session 。保存失败，但是对Book.get()的调用从当前的休眠 session 而不是数据库中加载实例。如果您检查了脏标志，则可以确认此检查isDirty()或调用refresh()从数据库中重新获取实例。