com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException：列'ID_category'不能为null

Question

com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException：列'ID_category'不能为null

我试图在表“产品”和“类别”之间建立连接是一对多的。但是对象产品中的类别条目，它不会被填充。为什么？

@Entity
@Table(name = "CATEGORY") 
public class Category implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue
@Column(name = "ID")
private int id;
@Column(name = "name")
private String name;
@OneToMany(fetch = FetchType.LAZY,mappedBy = "category")
private Set<Product> products = new HashSet<Product>(0);
public Category() { }

@Entity
@Table(name = "PRODUCTS")
public class Product implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue
@Column(name = "ID_PRODUCT")
private int id;
@Column(name = "name")
private String name;
@ManyToOne
@JoinColumn(name = "ID_category", nullable = true)
private Category category;
@ManyToOne
@JoinColumn(name = "ID_producer", nullable = true)
private Producer producer;
@Column(name = "description")
private String description;
@Column(name = "price")
private int price;
@Column(name = "number")
private Integer number;
@Column(name = "picture")
private String picture;

这是我的更新控制器。我更新了发现的产品。

 @Controller
    public class ProductUpdateController {
    private static final Logger log =    Logger.getLogger(ProductUpdateController.class);
    @Autowired
    private ProductService productService;
    @Autowired
    private CategoryService categoryService;
    @Autowired
    private ProducerService producerService;

    @RequestMapping(value = "/products/{id}/update.html", method = RequestMethod.GET)
    public String updateCourse(Model model, HttpSession session, HttpServletRequest request,
            @PathVariable("id") Integer productId) {
        Product product = (Product) productService.findProductById(productId);
        model.addAttribute(product);
        return "update";    }
    @RequestMapping(value = "/products/{id}/update.html", method = RequestMethod.POST)
    public String updateCoursePost(Model model, HttpSession session, HttpServletRequest request,
            @PathVariable("id") Integer productId, @Valid Product product, BindingResult result)
            throws AddressException, Exception {        
        product = productService.updateProduct(product);

这是我的观点页面。

     <form:form name='updateForm' commandName="product" onsubmit="return validate(this); " method="POST">
        <fieldset>
            <div class="form-group">
                <label class="control-label">Name</label>
                <div class="controls">
                    <form:input path="name" />
                </div>
            </div>
            <div class="form-group">
                <label class="control-label">Category</label>
                <div class="controls">
                    <select  name="category" class="span3">
                        <c:forEach var="cat" items="${listCategories}">
                            <option value="${cat}">${cat.name}</option>
                        </c:forEach>
                    </select>
                </div>
            </div>

这是我的那些表的sql脚本。

 CREATE TABLE `category` (
 `ID` int(11) NOT NULL,
 `name` varchar(255) NOT NULL
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1;


INSERT INTO `category` (`ID`, `name`) VALUES
(1, 'Sedan'),
(2, 'SUV'),
(3, 'Hatchback'),
(4, 'Crossover'),
(5, 'Minibus');

CREATE TABLE `producer` (
`ID` int(11) NOT NULL,
`name` varchar(30) NOT NULL,
`links` varchar(30) NOT NULL
) ENGINE=MyISAM DEFAULT CHARSET=latin1;

INSERT INTO `producer` (`ID`, `name`, `links`) VALUES
(1, 'Nissan', 'nissan.com'),
(2, 'Porsche', 'porsche.com'),
(5, 'Bentley', 'bentley.com');

CREATE TABLE `products` (
`ID_PRODUCT` int(11) NOT NULL,
`name` varchar(30) NOT NULL,
`ID_category` int(11) NOT NULL,
`ID_producer` int(11) NOT NULL,
`description` varchar(30) NOT NULL,
`price` int(11) NOT NULL,
`number` int(11) NOT NULL DEFAULT '10',
`picture` varchar(100) NOT NULL
) ENGINE=MyISAM DEFAULT CHARSET=latin1;

INSERT INTO `products` (`ID_PRODUCT`, `name`, `ID_category`, `ID_producer`, `description`, `price`, `number`, `picture`) VALUES
(1, 'Nissan 350z', 1, 1, '2.0', 30000, 10, '2009');

Answer 1

这似乎是关系的一个问题。 Product表具有外键category_id，即使您将其注释为可空，也不能在任何时候为null。