1. @MappedSuperclass

@MappedSuperclass
public abstract class CucdCriteriaBase {

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

    private String name;

    private String showName;

    @Enumerated(EnumType.STRING)
    private CompareCondition compareCondition;

    private String compareValue;

    //getter、setter

}

@Entity
@Table(name = "cucd_criteria_inspection")
public class CucdCriteriaInspection extends CucdCriteriaBase {

    private String type;

    //getter、setter
}

@MappedSuperclass 声明的父类不会对应数据库中的表，只有子类会跟数据库中的表对应

2. @OneToMany

2.1. 级联删除

@Entity
@Table(name = "cucd_criteria")
public class CucdCriteria {

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

    private String deviceType;

    private String company;

    private String description;

    @OneToMany(cascade = CascadeType.ALL, orphanRemoval = true)
    @JoinColumn(name = "criteria_id")
    private List<CucdCriteriaBackup> backups;

    @OneToMany(cascade = CascadeType.ALL, orphanRemoval = true)
    @JoinColumn(name = "criteria_id")
    private List<CucdCriteriaMetrics> metrics;

    //getter、setter
}

2.2. 使用中间表关联

@Entity
@Table(name = "cucd_criteria_part")
public class CucdCriteriaPart {

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

    @OneToMany
    @JoinTable(name = "cucd_criteria_part_backup", joinColumns = @JoinColumn(name = "part_id"), inverseJoinColumns = @JoinColumn(name = "backup_id"))
    private List<CucdCriteriaBackup> backups;

    @OneToMany
    @JoinTable(name = "cucd_criteria_part_metrics", joinColumns = @JoinColumn(name = "part_id"), inverseJoinColumns = @JoinColumn(name = "metrics_id"))
    private List<CucdCriteriaMetrics> metrics;

    //getter、setter
}

3. @ElementCollection

两个实体存在一对多关系且多的实体完全属于一的实体时使用，用DDD术语描述就是两个实体属于一个Aggregate并且一的实体是Aggregate Root

@Entity
@Table(name = "cucd_formula")
public class CucdFormula {

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

    private String name;

    @ElementCollection
    @CollectionTable(name = "cucd_formula_device_name", joinColumns = @JoinColumn(name = "formula_id"))
    @Column(name = "device_name")
    private Set<String> deviceNames;

    @ElementCollection
    @CollectionTable(name = "cucd_formula_notify_type", joinColumns = @JoinColumn(name = "formula_id"))
    @Enumerated(EnumType.STRING)
    @Column(name = "notify_type")
    private Set<NotifyType> notifyTypes;                        (1)

    @ElementCollection
    @CollectionTable(name = "cucd_formula_notifier", joinColumns = @JoinColumn(name = "formula_id"))
    private Set<Notifier> notifiers;                            (2)

    //getter、setter

    @Embeddable
    public static class Notifier {

        private Integer userId;

        private Integer orgId;

        //getter、setter
    }
}

  1. cucd_formula_notify_type 表有两列 formula_id 和 notify_type

  2. cucd_formula_notifier 表有三列 formula_id、user_id 和 org_id

使用Criteria API根据 @ElementCollection 声明的属性进行模糊查询

public class CucdFormulaService {
    public Page<CucdFormula> list(CucdFormula cucdFormula, Pageable pageable, String deviceName) {
        Specification<CucdFormula> specification = (root, query, criteriaBuilder) -> {
            List<Predicate> predicates = new ArrayList<>();
            if (StringUtils.hasText(cucdFormula.getName())) {
                predicates.add(criteriaBuilder.like(root.get(CucdFormula_.NAME), "%" + cucdFormula.getName() + "%"));
            }
            if (StringUtils.hasText(deviceName)) {
                Subquery<Long> subquery = criteriaBuilder.createQuery(CucdFormula.class).subquery(Long.class);
                Root<CucdFormula> subRoot = subquery.from(CucdFormula.class);
                subquery.select(criteriaBuilder.literal(1L))
                        .where(criteriaBuilder.equal(root.get(CucdFormula_.ID), subRoot.get(CucdFormula_.ID)),
                            criteriaBuilder.like(subRoot.join(CucdFormula_.DEVICE_NAMES), "%" + deviceName + "%"));
                predicates.add(criteriaBuilder.exists(subquery));
            }
            return criteriaBuilder.and(predicates.toArray(new Predicate[0]));
        };
        return cucdFormulaRepository.findAll(specification, pageable);
    }
}