为什么我得到一个空值？ （冬眠，春天）

【问题标题】：Why am I getting a null value? (HIBERNATE, SPRING)为什么我得到一个空值？ （冬眠，春天）
【发布时间】：2016-10-20 12:40:31
【问题描述】：

当我尝试添加新对象时，为什么 Hibernate 会检测到空值？我有一个具有字段对象类别的产品类。 Product 中的类别作为 category_id 存储在数据库中。这是我的产品课。 

@Entity
@Table(name = "PRODUCT")
public class Product implements java.io.Serializable {

/**
 * 
 */
private static final long serialVersionUID = 1L;

private long id;

private String upc;

private Category category;

private String name;

private String description;

private BigDecimal price;

public Product(){

}

public Product(String upc){
    this.upc = upc;
}

public Product(String upc, String name, BigDecimal price){
    this.upc = upc;
    this.name = name;
    this.price = price;
}

public Product(String upc, Category category, String name, String description, BigDecimal price) {
    super();
    this.upc = upc;
    this.category = category;
    this.name = name;
    this.description = description;
    this.price = price;
}

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

@Id @GeneratedValue
@Column(name = "id")
public long getId() {
    return id;
}

@Column(name = "upc", nullable = false)
public String getUpc() {
    return upc;
}

public void setUpc(String upc) {
    this.upc = upc;
}

@ManyToOne @NotNull
@JoinColumn(name = "category_id", referencedColumnName = "category_id")
public Category getCategory() {
    return category;
}

public void setCategory(Category category) {
    this.category = category;
}

@Column(name = "name")
public String getName() {
    return name;
}

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

@Column(name = "description")
public String getDescription() {
    return description;
}

public void setDescription(String description) {
    this.description = description;
}

@Column(name = "price")
public BigDecimal getPrice() {
    return price;
}

public void setPrice(BigDecimal price) {
    this.price = price;
}
}

这是我的类别类：

@Entity
@Table(name = "CATEGORY")
public class Category implements Serializable{

/**
 * 
 */
private static final long serialVersionUID = 1L;

private long id;
private String categoryId;
private String name;
private Set<Product> products;

public Category(){}

public Category(String categoryId, String name) {
    super();
    this.categoryId = categoryId;
    this.name = name;
}

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

@Id @GeneratedValue
@Column(name = "id")
public long getId() {
    return id;
}

@Column(name = "category_id")
public String getCategoryId() {
    return categoryId;
}

public void setCategoryId(String categoryId) {
    this.categoryId = categoryId;
}

@Column(name = "name")
public String getName() {
    return name;
}

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

@OneToMany
@JoinColumn(name = "category_id", insertable = false, updatable = false)
public Set<Product> getProducts() {
    return products;
}

public void setProducts(Set<Product> products) {
    this.products = products;
}
}

现在，当我使用 session.save(product) 方法时，它会为 Category 字段获取 null 值，但在使用本机 sql 时运行完美。我试图打印类别 ID 及其那里。这是我添加产品的代码：

@Override
public void addProduct(Product product) {

    System.out.println(product.getCategory().getCategoryId());

    Session session = sessionFactory.openSession();

    Transaction transaction = null;

    try {
        transaction = session.beginTransaction();

//          Query query =    session.createSQLQuery(DAOQuery.HQL_ADD_PRODUCT).setParameter("upc",   product.getUpc())
//                               .setParameter("category", product.getCategory().getCategoryId())
//                               .setParameter("name", product.getName()).setParameter("description", product.getDescription())
//                               .setParameter("price", product.getPrice());
//
//          query.executeUpdate();
        session.save(product);

        transaction.commit();
    } catch (HibernateException e) {
        if (transaction != null)
            transaction.rollback();

        e.printStackTrace();
    } finally {
        session.close();
    }
}

这是错误：

WARN: SQL Error: 1048, SQLState: 23000
Oct 20, 2016 8:30:15 PM org.hibernate.engine.jdbc.spi.SqlExceptionHelper logExceptions
ERROR: Column 'category_id' cannot be null
org.hibernate.exception.ConstraintViolationException: could not execute statement
at org.hibernate.exception.internal.SQLStateConversionDelegate.convert(SQLStateConversionDelegate.java:112)
at org.hibernate.exception.internal.StandardSQLExceptionConverter.convert(StandardSQLExceptionConverter.java:42)
at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:111)
at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:97)
at org.hibernate.engine.jdbc.internal.ResultSetReturnImpl.executeUpdate(ResultSetReturnImpl.java:207)
at org.hibernate.dialect.identity.GetGeneratedKeysDelegate.executeAndExtract(GetGeneratedKeysDelegate.java:57)
at org.hibernate.id.insert.AbstractReturningDelegate.performInsert(AbstractReturningDelegate.java:42)
at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:2840)
at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:3411)
at org.hibernate.action.internal.EntityIdentityInsertAction.execute(EntityIdentityInsertAction.java:81)
at org.hibernate.engine.spi.ActionQueue.execute(ActionQueue.java:597)
at org.hibernate.engine.spi.ActionQueue.addResolvedEntityInsertAction(ActionQueue.java:232)
at org.hibernate.engine.spi.ActionQueue.addInsertAction(ActionQueue.java:213)
at org.hibernate.engine.spi.ActionQueue.addAction(ActionQueue.java:256)
at org.hibernate.event.internal.AbstractSaveEventListener.addInsertAction(AbstractSaveEventListener.java:318)
at org.hibernate.event.internal.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:275)
at org.hibernate.event.internal.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:182)
at org.hibernate.event.internal.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:113)
at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:192)
at org.hibernate.event.internal.DefaultSaveEventListener.saveWithGeneratedOrRequestedId(DefaultSaveEventListener.java:38)
at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:177)
at org.hibernate.event.internal.DefaultSaveEventListener.performSaveOrUpdate(DefaultSaveEventListener.java:32)
at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:73)
at org.hibernate.internal.SessionImpl.fireSave(SessionImpl.java:667)
at org.hibernate.internal.SessionImpl.save(SessionImpl.java:659)
at org.hibernate.internal.SessionImpl.save(SessionImpl.java:654)
at com.qbryx.dao.ProductDaoHQLImpl.addProduct(ProductDaoHQLImpl.java:138)
at com.qbryx.service.ManagerServiceImpl.addProduct(ManagerServiceImpl.java:24)
at com.qbryx.controller.ManagementController.createProduct(ManagementController.java:62)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.springframework.web.bind.annotation.support.HandlerMethodInvoker.invokeHandlerMethod(HandlerMethodInvoker.java:180)
at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod(AnnotationMethodHandlerAdapter.java:440)
at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.handle(AnnotationMethodHandlerAdapter.java:428)
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:963)
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:897)
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:872)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:648)
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:292)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at org.springframework.orm.hibernate5.support.OpenSessionInViewFilter.doFilterInternal(OpenSessionInViewFilter.java:151)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:212)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:141)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:616)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:528)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1100)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:687)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1520)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1476)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Unknown Source)
Caused by: java.sql.SQLException: Column 'category_id' cannot be null
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:2975)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1600)
at com.mysql.jdbc.ServerPreparedStatement.serverExecute(ServerPreparedStatement.java:1129)
at com.mysql.jdbc.ServerPreparedStatement.executeInternal(ServerPreparedStatement.java:681)
at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:1368)
at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:1283)
at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:1268)
at org.hibernate.engine.jdbc.internal.ResultSetReturnImpl.executeUpdate(ResultSetReturnImpl.java:204)
... 63 more

我似乎找不到问题所在。我需要帮助。谢谢。

【问题讨论】：

  • 您在类别属性中设置了@NotNull 验证

标签： java spring hibernate


【解决方案1】：

错误提示categoryId 为空，而您的数据库配置为非空。

您使用@Id @GeneratedValue 标记了id，Hibernate 会为此生成一个新的 long 值，但如果您不为 categoryId 提供值，它将不会生成。

您应该将@Id @GeneratedValue 移动到categoryId 或在构建它时提供一个值。

此外，我建议你检查你的设计，因为在你的课堂上同时拥有id 和categoryId 会让人感到困惑；归根结底，每个人都会将属性 id 称为“类别 ID”，而您将不知道他们指的是该 ID 还是“类别 ID”。

【讨论】：

    【解决方案2】：

    您没有提供为类别生成 Id 的正确策略。

    如果您的数据库使用序列，您可以将 id 映射为：

    @GeneratedValue(strategy = GenerationType.IDENTITY)

    如果没有，则创建生成策略

    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "category_generator")
@SequenceGenerator(name="category_generator", sequenceName = "category_seq")

    【讨论】：

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