java - 如何查找/更改 hibernate 查询

Question

我正在尝试修复由我的数据库上的 Hibernate 查询引起的错误，但我似乎无法找到该查询的来源。在启用sql log on hibernate 后，我找到了错误所在，但不知道如何修复。

Hibernate query (eclipse log) "update students_classes set student_id=null where student_id=?"

throwing: ERROR [org.hibernate.engine.jdbc.spi.SqlExceptionHelper] (http-localhost-127.0.0.1-8080-2) Column 'student_id' cannot be null

错误在这一行抛出:

student = studentDAO.save(student);

保存从何而来

public Entity save(Entity entity) throws Exception {
        Entity result = null; 
        try {   
            trimAllStrAttributes(entity);
            result = em.merge(entity);
        } catch (Exception e) {
            logger.error("Exception in AbstractDAO", e);
            throw e;
        }

        return result;
    }


private void trimAllStrAttributes(Entity product) throws IntrospectionException, IllegalAccessException, InvocationTargetException, NoSuchMethodException {
        final Class c = product.getClass();
        for (PropertyDescriptor propertyDescriptor : Introspector.getBeanInfo(c, Object.class).getPropertyDescriptors()) {
            Method method = propertyDescriptor.getReadMethod();
            if (method != null) {
                String name = method.getName();

                // If the current level of Property is of type String
                if (method.getReturnType().equals(String.class)) {
                    String property = (String) method.invoke(product);
                    if (property != null) {
                        try {
                            Method setter = c.getMethod("set" + name.substring(3), new Class<?>[] { String.class });
                            if (setter != null) {
                                setter.invoke(product, property.trim());
                            }
                        } catch (NoSuchMethodException nsme) {
                        }
                    }
                }
            }
        }
    }

这可能是一个映射问题，所以这是我的实体:

学生类(class)

@Column(name = "student_id")
private Long studentId;

@Column(name = "classes_id")
private Long classesId;

学生

@AuditJoinTable
    @ManyToMany
    @JoinTable(name = "students_classes", 
    joinColumns = @JoinColumn(name = "student_id", referencedColumnName = "id"), 
    inverseJoinColumns = @JoinColumn(name = "classes_id", referencedColumnName = "id"))
    private List<Classes> classes;

@NotAudited
@OneToMany
@JoinColumn(name = "student_id")
private List<StudentClasses> studentsClasses;

我该怎么办？改变hibernate的query(去哪里找？)还是mapping层面有问题？

Answer 1

错误会自行解释:

throwing: ERROR [org.hibernate.engine.jdbc.spi.SqlExceptionHelper] (http-localhost-127.0.0.1-8080-2) Column 'student_id' cannot be null

根据您的其他映射，我可以肯定地说 studentId 是表的主键，因此，如果您不知道新实体必须具有的 ID，则必须标记该字段以使 hibernate 映射它:

将 studentId 标记为 id 并添加一个自动生成的值:

@Id
@GeneratedValue(strategy=GenerationType.AUTO)
private Long studentId;

Hibernate 定义了五种标识符生成策略:

• AUTO - 标识列、序列或表，具体取决于基础数据库
• TABLE - 包含 id 的表
• IDENTITY - 身份列
• SEQUENCE - 序列
• identity copy – 身份是从另一个实体复制的