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- anno : - https://chatgpt.com/c/1375c062-4b67-437d-860b-e065a2980f57

Hibernate

Annotation

Common Annotation

  • @Entity(name="new_entityname"), @version feild
  • @Basic(fetch=FetchType.EAGER,optional=true).
    • this is already added by default on all column.
    • basic mapping, field to a db column.
  • @Table(name="new_tablename")
  • @Column(name="new_colname", updateble=f/t), more
    • Lenght=255, string-valued column length. / @Length
    • Precision and Scale. for decimal feild.
  • @Transient

relationship

  • @OneToOne,
  • @OneToMany, @ManyToOne,
  • @JoinTable and @JoinColumn()
  • @OrderBy("colInManySide ASC") Sorting Children within Each Parent

  • @Fetch @batchSize - use together in relation : 1-2-M,etc

  • @ManyToMany : Add FK and create JoinTable bts.

  • @WhereJoinTable(clause = "columnInJoinTable='value-1'")

identifier

Inheritance

  • @MappedSuperclass on parent class
  • @Inheritance(strategy = InheritanceType.SINGLE_TABLE) : on parentClass
  • @DiscriminatorColumn(name="columnName",discriminatorType = DiscriminatorType.INTEGER) : on parentClass
  • @DiscriminatorValue("1") : on ChildClass

Performance

  • q.setFetchSize(10)
  • @BatchSize(size = 20) at Entity level for All operations.
  • custom code to achieve batch behaviour :
  • for loop >> on iteration 20, perform flush amd clear em/session.
  • Small Fetch Size: May lead to more frequent database calls, increasing network latency and overhead.
  • Large Fetch Size: Reduces the number of database calls but consumes more memory as more rows are loaded into memory at once.
  • @BatchSize on Entity level
  • option for relation/many-side:

  • @Fetch

    • (FetchMode.SELECT) : https://chatgpt.com/c/1375c062-4b67-437d-860b-e065a2980f57
    • fetch associated entities lazily, to avoid loading unnecessary data upfront.
    • optimizing performance when dealing with large collections.
    • (FetchMode.Join) : load early

  • @BatchSize

    • Use along with @Fetch.
    • @OneToMany(mappedBy = "order") @BatchSize(size = 10) private List items;
    • optimize the loading of collections.
    • instead of issuing separate SELECT queries for each item, Hibernate will fetch 10 items at a time, reducing the number of queries executed.
    • but may increase memory usage, if batch size is big.

  • @OneToMany(fetch = FetchType.LAZY/EAGER), etc

  • @Basic(fetch=FetchType.EAGER)

Convertor (rarely used)

  • @Convert (converter=abc.class)
  • more like binder - which jackson for JSON<-->Object(DTO)
  • converter for DB::table<-->Object(Entity)
  • use case : performing encryption/decryption, data transformations, that are NOT directly supported by JPA, etc
  • implement AttributeConverter , override:
    • dbType convertToDatabaseColumn(entityType)
    • entityType convertToEntityAttribute(dbType)
  • @Lob byte[]
  • @Temporal(TemporalType.DATE) private Date birthDate;
  • temporal, meaning relating to time.
  • java has seperate set of API(Java.sql.*), to deal with DB Date/time eg: connection code, etc
  • java.util.* and java.time.* <--convert--> Java.sql.*
  • @Enumerated(EnumType.STRING/ORDINAL) MyEnum
  • enums to their ordinal values or names
  • hibernate automatically converts to enum value, if not mentioned.
  • Automatic/inbuilt conversion by Hibernate :
  • Boolean to int (t-1, f-0)
  • Boolean to String(t-"true")
  • java.time.LocalDate to java.sql.Date <<<
  • java.time.LocalDateTime to java.sql.Timestamp <<<
  • enum to string/ordinal. String/int var1

Other

  • @embedded and @embeddable
  • define a class whose instances can be embedded in an entity.
  • This class does not have its own table but shares the table of the owning entity.
  • @Embedded @AttributeOverrides : use to override columnName whiling embedding 
    @Embedded  
@AttributeOverrides({
      @AttributeOverride(name = "street", column = @Column(name = "home_street")),
      @AttributeOverride(name = "city", column = @Column(name = "home_city")), ...
  })
  • @SqlResultSetMapping : Map @NamedNativeQuery result to target(Entity/Tuple)

Annotation from SB-Jpa-Data-starter

  • @EnableTransactionManagement
  • @Transactional
  • @Query + @Param
  • @QueryHints({@QueryHint(name = "org.hibernate.fetchSize", value = "10")})
  • pending
  • program on inheritance
  • program on relationship