[英]Auto generate id in Spring MVC
I'm trying to save data collected by a JSP page within a database (Postgres).我正在尝试将 JSP 页面收集的数据保存在数据库(Postgres)中。 At first I tried to insert any values manually (including id
) in a form and I had no problem saving the data in my db.起初,我尝试在表单中手动插入任何值(包括id
),并且将数据保存在我的数据库中没有问题。 Now I'm trying to auto generate the id
values, but I'm a little bit confused about how to do it properly.现在我正在尝试自动生成id
值,但我对如何正确执行它有点困惑。
My model - Product我的模型 - 产品
public class Product {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
private String description;
private double price;
@DateTimeFormat(pattern = "dd/MM/yyyy")
private Date date;
public Product() { }
public Product(Long id, String description, double price, Date date) {
this.id = id;
this.description = description;
this.price = price;
this.date = date;
}
//getters and setters
}
My controller - DBConnection我的控制器 - DBConnection
@Controller
public class DBConnection {
@Autowired
private ProductDao prDao;
@RequestMapping(value = "/newproduct", method = RequestMethod.GET)
public ModelAndView showForm() {
Product product = new Product();
return new ModelAndView("newproduct", "product", product);
}
@RequestMapping(value = "/newproduct", method = RequestMethod.POST)
public ModelAndView submitForm(@ModelAttribute("product") Product product) {
ModelAndView mav = new ModelAndView();
prDao.addProduct(product.getId(), product.getDescription(), product.getPrice(), product.getDate());
mav.setViewName("product");
mav.addObject("product", product);
return mav;
}
}
ProductDaoImpl ProductDaoImpl
public class ProductDaoImpl implements ProductDao {
private DataSource dataSource;
private JdbcTemplate jdbcTemplate;
@Override
public void setDataSource(DataSource ds) {
this.dataSource = ds;
this.jdbcTemplate = new JdbcTemplate(dataSource);
}
@Override
public void addProduct(Long id, String description, double price, Date date) {
jdbcTemplate.update("INSERT INTO products values(?, ?, ?, ?)", id, description, price, date);
}
}
My form in newproduct.jsp我在 newproduct.jsp 中的表单
<form:form method="POST" action="newproduct" modelAttribute="product">
<table>
<tr>
<td><form:label path="description">Description</form:label></td>
<td><form:input path="description" /></td>
</tr>
<tr>
<td><form:label path="price">Price</form:label></td>
<td><form:input path="price" /></td>
</tr>
<tr>
<td><form:label path="date">Date (dd/mm/yyyy)</form:label></td>
<td><form:input path="date" /></td>
</tr>
<tr>
<td><input type="submit" value="Submit" /></td>
</tr>
</table>
</form:form>
Error when I submit the form提交表单时出错
org.springframework.web.util.NestedServletException: Request processing failed; nested exception is org.springframework.dao.DataIntegrityViolationException: PreparedStatementCallback; SQL [INSERT INTO products values(?, ?, ?, ?)]; ERROR: null values in column "id" violates not-null constraint
Detail: The row contains error (null, nnvfe, 10.00, 2010-10-10).; nested exception is org.postgresql.util.PSQLException: ERROR: null values in column "id" violates not-null constraint
Detail: The row contains error (null, nnvfe, 10.00, 2010-10-10).
I think the problem is in the addProduct
method: the id
value isn't yet created when I tried to get it.我认为问题出在addProduct
方法中:当我尝试获取它时,还没有创建id
值。
How can I implements an auto generated id?如何实现自动生成的 id? Is the JPA annotation the correct way to do that thing? JPA 注释是做那件事的正确方法吗?
Now I'm trying to auto generate the id values, but I'm a little bit confused about how to do it properly现在我正在尝试自动生成 id 值,但我对如何正确执行它有点困惑
If you want to automatically generate the id
, then do not provide one, even it's null
.如果要自动生成id
,则不要提供,即使它是null
。 So, remove the id
from addProduect
method:因此,从addProduect
方法中删除id
:
@Override
public void addProduct(String description, double price, Date date) {
jdbcTemplate.update("INSERT INTO products values(?, ?, ?)", description, price, date);
}
Also, make your id
field auto-increment
, as in this question .另外,使您的id
字段auto-increment
,如在此问题中。
Or, change the addProduct
method and use EntityManager#persist
method:或者,更改addProduct
方法并使用EntityManager#persist
方法:
@Override
public void addProduct(Product product) {
entityManager.persist(product);
}
About the error:关于错误:
ERROR: null values in column "id" violates not-null constraint错误:“id”列中的空值违反非空约束
Since your form does not take the id
value from the client, the /newproduct
endpoint would have a Product
with null
as its id
value:由于您的表单不从客户端获取id
值,因此/newproduct
端点将有一个带有null
作为其id
值的Product
:
@RequestMapping(value = "/newproduct", method = RequestMethod.POST)
public ModelAndView submitForm(@ModelAttribute("product") Product product) { ... }
Then you pass this null
value as the parameter to the addProduct
method:然后将此null
值作为参数传递给addProduct
方法:
prDao.addProduct(product.getId(), ...)
And finally addProduct
would try to save that null
value as the value of the Primary Key , which has a Non-Null constraint, so you're got that error.最后addProduct
会尝试将该null
值保存为Primary Key的值,该值具有Non-Null约束,因此您会遇到该错误。
Also, using Entity objects as the means of communication with client, eg Product
, is not a good practice.此外,使用Entity对象作为与客户端通信的手段,例如Product
,不是一个好的做法。 Try to define some auxiliary abstractions like Forms or DTOs and use them for form handling or response assembling.尝试定义一些辅助抽象,如 Forms 或 DTO,并将它们用于表单处理或响应组装。
Error-Caused by: java.sql.SQLSyntaxErrorException: Specified key was too long; max key length is 1000 bytes
operation perform-
@Id
private String userName;
Solution解决方案
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