java JPA：从另一个对象访问对象返回null

Question

我想从密钥访问上面的实体密钥

这种关系是：

规则包含一个术语规则。 每个TermRule包含一个规则和一个可变配置

只有VariableConfiguration包含一个变量

我想从TermRule中捕获变量

我试着这样做：

termRule.getVariableConfiguration().getVariable()并接收空值

有可能得到一个项的变量吗

public class Rule extends PersistentObject {

    private static final long serialVersionUID = 7852189080136935020L;

    @Column (name ="NAME", nullable = false)
    private String namerule;
    
    @OneToMany(mappedBy = "rule", fetch = FetchType.LAZY)
    private List<TermRule> termRule;
}
//getters and setters

public class TermRule extends PersistentObject implements Comparable<TermRule> {
    private static final long serialVersionUID = 336244667983772321L;

    @ManyToOne
    @JoinColumn(name = "ID_RULE", referencedColumnName = "ID", nullable = false)
    private Rule rule;
    
    @OneToOne 
    @JoinColumn (name ="ID_VAR_CONF", referencedColumnName = "ID", nullable = true)
    private VariableConfiguration variableConfiguration;
}

public abstract class VariableConfiguration extends PersistentObject {

    private static final long serialVersionUID = -4967631633375881594L;
    
    @ManyToOne
    @JoinColumn(name = "ID_VARIAVEL", referencedColumnName = "ID", nullable = false)
    private Variable variable;
        
    @OneToOne (mappedBy= "variableConfiguration", cascade = CascadeType.REMOVE, fetch = FetchType.LAZY)
    private TermRule termRule;
}

@DiscriminatorValue("Triangle")
public class Triangle extends VariableConfiguration {
}

public class Variable extends PersistentObject {

    private static final long serialVersionUID = -1172539974105845401L;

    @Column (name = "NOME", nullable = false)
    private String name;

    @OneToMany (mappedBy= "variable", cascade = CascadeType.REMOVE, fetch = FetchType.LAZY)
    private List<VariableConfiguration> variableConfiguration;
}