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hibernate [2020/04/29 09:28] – skipidarhibernate [2023/07/14 12:42] (current) – [Transactional] skipidar
Line 71: Line 71:
  
  
-Introduce a Superclass with an ID+ 
 +Introduce a Superclass with an ID.
 <sxh java> <sxh java>
  
Line 84: Line 85:
 </sxh> </sxh>
  
 +=== Bidirectional Many-To-Many ===
 +Here Both Entities Campus and CampuPart have a Link on each other.
 +This is called a BiDirectional modeling
  
-Introduce an ECampus+  * Owning-side vs. inverse-side https://www.baeldung.com/hibernate-one-to-many
  
-<sxh java> 
  
-@Entity(name="ECampus") +== Owning - with Join Table ==
-@Table(name = "campuses", schema = "public") +
-public class ECampus extends ELocation  {+
  
-  @OneToMany(mappedBy = "campus", cascade = {CascadeType.MERGE, CascadeType.PERSIST, CascadeType.REFRESH}) +Introduce an **ECampusPart** 
-  private Set<ECampusPart> campusParts = new HashSet<>(); +Here the **JoinTable** is on CampusPart, so it is the **owning-side** of the connection. 
-   +
-} +
-</sxh> +
- +
- +
-Introduce an ECampusPart+
  
 <sxh java> <sxh java>
Line 127: Line 122:
  
  
 +Using "JoinTable" results in the creation of a special table
 +<sxh java>
  
 +@Entity(name = "ECampusPart")
 +@Table(name = "campusparts", schema = "public")
 +public class ECampusPart extends ELocation  {
  
 +  @ManyToOne(cascade = {CascadeType.MERGE, CascadeType.PERSIST, CascadeType.REFRESH})
 +  @JoinTable(
 +          name = "campus_campuspart",
 +          joinColumns = {@JoinColumn(name = "campuspart_id")},
 +          inverseJoinColumns = {@JoinColumn(name = "campus_id")}
 +  )
 +  private ECampus campus;
 +
 +</sxh>
 +
 +Results in
 +
 +**campuses**
 +^dtype^id^object_type^name^
 +|ECampusPart|497ffe9a-51bb-4ab4-bc3d-b8923d620703|CampusPart|ViennaSmart City Campus front part|
 +
 +
 +**campusparts**
 +^dtype^id^object_type^name^
 +|ECampus|dbadab87-7b6d-4e8b-b2c8-0663d68dfe7b|Campus|ViennaSmart City Campus|
 +
 +
 +**campus_campuspart**
 +^campus_id^campuspart_id^
 +|497ffe9a-51bb-4ab4-bc3d-b8923d620703|dbadab87-7b6d-4e8b-b2c8-0663d68dfe7b|
 +
 +
 +
 +== Owning-side - with embedded foreign key ==
 +
 +Omitting the "JoinTable" results in embedding the Foreign key **campus_id** - into the **CampusPart** table
 +
 +<sxh java>
 +
 +@Entity(name = "ECampusPart")
 +@Table(name = "campusparts", schema = "public")
 +public class ECampusPart extends ELocation  {
 +
 +  @ManyToOne(cascade = {CascadeType.MERGE, CascadeType.PERSIST, CascadeType.REFRESH})
 +  private ECampus campus;
 +
 +</sxh>
 +
 +
 +Results in 
 +
 +**campuses**
 +^dtype^id^object_type^name^campus_id^
 +|ECampusPart|497ffe9a-51bb-4ab4-bc3d-b8923d620703|CampusPart|ViennaSmart City Campus front part|dbadab87-7b6d-4e8b-b2c8-0663d68dfe7b|
 +
 +
 +**campusparts**
 +^dtype^id^object_type^name^
 +|ECampus|dbadab87-7b6d-4e8b-b2c8-0663d68dfe7b|Campus|ViennaSmart City Campus|
 +
 +
 +
 +
 +
 +== Inverse-side ==
 +
 +Introduce an **ECampus**.
 +Here the **mappedBy** is on Campus, so it is the **inverse-side** of the connection. 
 +
 +<sxh java>
 +
 +@Entity(name="ECampus")
 +@Table(name = "campuses", schema = "public")
 +public class ECampus extends ELocation  {
 +
 +  @OneToMany(mappedBy = "campus", cascade = {CascadeType.MERGE, CascadeType.PERSIST, CascadeType.REFRESH})
 +  private Set<ECampusPart> campusParts = new HashSet<>();
 +  
 +}
 +</sxh>
 +
 +
 +
 +
 +
 +===== Warning: bidirectional relationships ======
 +
 +ManyToMany relationships can lead to inconsitancies when
 +  * settings links back
 +  * there are multiple entities linking, back to parents 
 +  * entities have inconsistant list of members
 +{{https://s3.eu-central-1.amazonaws.com/alf-digital-wiki-pics/sharex/2020-05-05_12-01-00.png}}
 +
 +
 +
 +===== Transactional =====
 +
 +Seems like when wiring entities, which are affected on both sides - it should happen in 1 transaction.
 +
 +In Spring boot you need to annotate a method with ''@Transactional''
 +
 +At a high level, Spring creates proxies for all the classes annotated with @Transactional, either on the class or on any of the methods. The proxy allows the framework to inject transactional logic before and after the running method, mainly for starting and committing the transaction.
 +
 +https://www.baeldung.com/transaction-configuration-with-jpa-and-spring
 +
 +
 +https://thorben-janssen.com/transactions-spring-data-jpa/
 +
 +<sxh java>
 +@Service
 +@Getter
 +public class EquipmentService {
 +
 +    @Autowired
 +    private EquipmentRepository equipmentRepository;
 +     
 +    @Transactional
 +    public void updateEquipmentFeeds(ResourcePK equipmentFeeds, ResourcePK equipmentTarget) {
 +        Assert.isTrue(equipmentFeeds.getPartitionId().equals(equipmentTarget.getPartitionId()), "Only allow feeds in same partition");
 +        Equipment e1 = equipmentRepository.findById(equipmentFeeds).get();
 +        Equipment e2 = equipmentRepository.findById(equipmentTarget).get();
 +        e1.getFeeds().add(e2);
 +        equipmentRepository.save(e1);
 +    } 
 +}
 +</sxh>
 +
 +
 +
 +==== ManyToMany with composite key to self ====
 +
 +<sxh java>
 +
 +    @ManyToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
 +    @JoinTable(name="FeedsRel",
 +            joinColumns={
 +                    @JoinColumn(
 +                            name = "feedsrel_child_id",
 +                            referencedColumnName = "id"),
 +                    @JoinColumn(
 +                            name = "feedsrel_child_partitionId",
 +                            referencedColumnName = "partitionId")
 +            })
 +    private Set<Equipment> feeds = new HashSet<Equipment>();
 +
 +
 +    // Associations marked as mappedBy must not define database mappings like @JoinTable or @JoinColumn
 +    @ManyToMany( cascade = CascadeType.ALL, mappedBy="feeds", fetch = FetchType.EAGER)
 +    private Set<Equipment> fedBy = new HashSet<Equipment>();
 +</sxh>
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