我正在尝试配置我的实体，但是hibernate会引发以下异常：

org.hibernate.MappingException: Could not determine type for: com.sd.entity.SDUserProductAcess,   at table: SDUser, for columns: [org.hibernate.mapping.Column(productAccess)]
[PersistEngine] Failed to initialize persistence engine!java.lang.NullPointerException

这些是我的实体：

@Entity
@Inheritance(strategy = InheritanceType.JOINED)
public class SDObject
{

@Id
@GeneratedValue
private long sdId;
private String sdType;

public long getSdId()
{
    return sdId;
}

public void setSdId(long sdId)
{
    this.sdId = sdId;
}

public String getSdType()
{
    return sdType;
}

public void setSdType(String sdType)
{
    this.sdType = sdType;
}
}

下一个：

@Entity
public class SDUser extends SDObject
{

@Column(unique = true)
private String code;
private String password;
private SDUserProductAcess productAccess;

public String getCode()
{
    return code;
}

public void setCode(String code)
{
    this.code = code;
}

public String getPassword()
{
    return password;
}

public void setPassword(String password)
{
    this.password = password;
}

@OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY)
public SDUserProductAcess getProductAccess()
{
    return productAccess;
}

public void setProductAccess(SDUserProductAcess productAccess)
{
    this.productAccess = productAccess;
}

最后一个：

@Entity
public class SDUserProductAcess extends SDObject
{

private boolean adm;

public boolean isAdm()
{
    return adm;
}

public void setAdm(boolean adm)
{
    this.adm = adm;
}
}

Hibernate无法确定位于SDUser实体中的productAccess列的类型。我是Hibernate的新手，我不知道发生了什么。

我应该提供某种ID吗？

谢谢！！