Question

我将数据保存到我的cassandra数据库时出现问题，我收到了这个错误还有我的代码：

class User {
    String firstName
    String lastName
    List books
    static hasMany = [books:Book]

}

class Book {
        String title
        static belongsTo = [author : User]
}

class BootStrap {

        def init = { servletContext ->
            def user01= new User(firstName: "Abderrahime",lastName: "FARHANE")
            def book = new Book(title: "test")
            def book2 = new Book(title: "test2")

            user01.addToBooks(book)
            user01.addToBooks(book2)
            user01.save(flush: true)


            def user02= User.findById(user01.id)
            println(user02.books)
        }
        def destroy = {
        }
 }

| Running application...
ERROR org.springframework.boot.SpringApplication - Application startup failed
java.lang.IllegalArgumentException: argument type mismatch
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_72]
    at

Answer 1

从List books课程中删除User。您已经通过static hasMany = [books:Book]

声明了一系列图书

Answer 2

我几乎可以肯定你没有发布完整的堆栈跟踪。

但是，让我们一步一步检查你的代码并修复它：

    def init = { servletContext ->
        def user01= new User(firstName: "Abderrahime",lastName: "FARHANE")

        def book = new Book(title: "test")
        def book2 = new Book(title: "test2")
        //if you want to add any of these books to user01, 
        //you should first persist (save) books in database

        //but you should remember also that 
        //each instance of Book belongs to specified User
        //so author of Book can not be null
        //so first you need to save your user
        user01.save(flush: true)

        //then save your books
        book.author = user01
        book.save(flush: true)

        book2.author = user01
        book2.save(flush: true)

        //then add them (books) to user:
        user01.addToBooks(book)
        user01.addToBooks(book2)
        user01.save(flush: true)

        //now it should work:
        def user02= User.findById(user01.id)
        println(user02.books)
    }

grails acess数组数据

2 个答案: