JPA删除实体的方法

如果我删除这样的实体：

public void remove(Case lawsuit) {
    Case c = entityManager.find(Case.class, lawsuit.getId());
    entityManager.remove(c);
}

那么它不会被删除，但如果是这样的话：

public void remove(Case lawsuit) {
    Case c = entityManager.find(Case.class, lawsuit.getId());

    entityManager.getTransaction().begin();
    entityManager.remove(c);
    entityManager.getTransaction().commit();
}

它通常被删除。为什么这是我可以删除的唯一方法？这是实体本身：

@Entity
@Table(name = "cases")
public class Case {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private long id;

    private String caseNumber;

    private String dataI;

    private String dataII;

    private String dataIII;

    @ManyToOne
    @JoinColumn(name = "judgeID")
    private Judge judge;

    @ManyToOne
    @JoinColumn(name = "lawyerID")
    private Lawyer lawyer;

    @ManyToOne
    @JoinColumn(name = "clientID")
    private Client client;

    @Enumerated(value = EnumType.ORDINAL)
    private CaseStatus statusI;

    @Enumerated(value = EnumType.ORDINAL)
    private CaseStatus statusII;

    @Enumerated(value = EnumType.ORDINAL)
    private CaseStatus statusIII;

    private String document;

    //геттеры, сеттеры
}