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假设有两个表 PRODUCT 和 VENDOR。它是 OnetoMany 映射（基于注释）。有一个名为 PRODUCT_VENDOR 的中间表。（产品到供应商是一对多）

供应商在产品创建之前创建。当要创建产品时，用户需要从现有数据中选择供应商。

我的问题是当我要再次保存产品对象（设置了供应商）时，数据将插入到供应商表中。（此时只需要向产品表和中间表插入数据）。

如何防止再次向 VENDOR 表插入数据？

编码

以下是产品

产品实体

@Entity
@Table(name = "product")
public class Product {

    @Id
    @GeneratedValue
    @Column(name = "id")
    private int id;

    @Column(name = "name")
    private String name;

    @Column(name = "journey")
    private String journey;

    @OneToMany(cascade = CascadeType.ALL)
    @JoinTable(name = "product_vendor", joinColumns = { @JoinColumn(name = "product_id") }, inverseJoinColumns = { @JoinColumn(name = "vendor_id") })
    private Set<Vendor> productVendors = new HashSet<Vendor>(0);


    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getJourney() {
        return journey;
    }

    public void setJourney(String journey) {
        this.journey = journey;
    }

    public Set<Vendor> getProductVendors() {
        return productVendors;
    }

    public void setProductVendors(Set<Vendor> productVendors) {
        this.productVendors = productVendors;
    }

}

然后在控制器类中。（我使用 Spring 作为业务层）

@Controller
public class ProductController {

    @Autowired
    ProductService productService;

    @Autowired
    ProductFormValidator productFormValidator;

    @Autowired
    VendorService vendorService;

    @RequestMapping(value = "/createProduct", method = RequestMethod.GET)
    public ModelAndView createProduct() {
        ModelAndView mav = new ModelAndView("CreateProduct");
        Product product = new Product();
        List<Vendor> allVendors = vendorService.getAllVendors();
        mav.addObject("product", product);
        mav.addObject("allVendors", allVendors);
        return mav;
    }

    @RequestMapping(value = "/createProduct", method = RequestMethod.POST)
    public String createProduct(@ModelAttribute("product") Product product,
            BindingResult result,@RequestParam("allVendors") String[] vendors) {        

        if(vendors != null && vendors.length > 0){
            Set<Vendor> allVendors = new HashSet<Vendor>();
            for(String id : vendors){
                System.out.print("##### vendor id ###  = "+id);
                Vendor vendor = new Vendor();
                vendor.setId(Integer.parseInt(id));
                allVendors.add(vendor);
            }
            product.setProductVendors(allVendors);
        }

        productFormValidator.validate(product, result);
        if (result.hasErrors()) {
            System.out.println(result.getFieldErrors());
            System.out.println(result.getGlobalErrors());
            return "CreateProduct";
        }
        System.out.println("### createProduct  in Controller ## ");
        productService.createProduct(product);
        return "redirect:createProduct.do";
    }

}

并在视图中。(jsp)

<%@ include file="header.jsp"%>
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
<%@ taglib uri="http://www.springframework.org/tags/form" prefix="form"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Create Product</title>
</head>
<body>
    <h4>Create Product</h4>
    <form:form commandName="product" method="POST"
        action="createProduct.do">
        <fieldset>
            <legend>Basic details</legend>
            <ul>
                <li><label for=name>Name</label> <form:input path="name"
                        type="text" required="true" placeholder="Name" />
                    <form:errors path="name" cssStyle="color:red"></form:errors></li>
                <li><label for=journey>Journey</label> <form:input
                        path="journey" type="text" required="true" placeholder="Journey" />
                    <form:errors path="journey" cssStyle="color:red"></form:errors></li>
                <li><label for=vendor>Vendor</label>


                 <c:forEach var="vendor" items="${allVendors}">
                    <input type="checkbox" name="allVendors" value="${vendor.id}"/>${vendor.name}
                </c:forEach>

                    <form:errors path="journey" cssStyle="color:red"></form:errors></li>                
            </ul>
        </fieldset>
        <fieldset>
            <button type=submit>Save Product</button>
        </fieldset>
    </form:form>
</body>
</html>

最后在dao层，

public void createProduct(Product product) {
   sessionFactory.getCurrentSession().save(product);
   System.out.println("# product name =  "+product.getName());
   System.out.println("# productDaoImpl #### New product Created #### ");

}

谢谢。

4

1 回答 1

1

我解决了这个问题。我们必须把

@OneToMany(cascade = CascadeType.MERGE)
于 2013-11-01T12:12:28.167 回答