hibernate-primary-key

Hibernate Primary Key

• Overview
  • Primary Keys in Hibernate
  • Which Primary Keys to Use?
• Auto Incremented Primary Key
• Vendor Specific Flyway Migrations
• UUID Primary Key
• UUID RFC 4122 Primary Key
• Natural Primary Key
• Composite Primary Key
• Embedded Composite Primary key

Overview

Primary Keys in Hibernate

We use annotation for specify the primary key with Hibernate:

@Id
@GeneratedValue(strategy = Generation.AUTO)

There are different primary keys can be used:

• Numeric Primary Keys
  • GenerationType.AUTO: let Hibernate pick - best practice is to specify
  • GenerationType.SEQUENCE: use database sequence (this is NOT a feature of MySQL)
  • GenerationType.IDENTITY: use auto-incremented database columns
  • GenerationType.TABLE: use database table to simulate sequence
• UUID Primary Keys
  • Common to use as primary key, it can help index performance.
  • The drawback is the UUID primary keys use more disk space.
  • Hibernate implements a custom generator by default, but it can be configured to generate a IETF RFC 4122 compliant UUID.
• Natural Primary Keys
  • A unique value with business meaning outside of the database.
  • A UPC or ISBN could be considered a natural key, since both are expected to be unique.
  • It's common in old legacy databases, but it's NOT considered the best practice.
• Composite Primary Keys
  • Two values with business meaning combined to make a unique value
  • It's common in old legacy databases, but it's NOT considered the best practice.

Which Primary Keys to Use?

• Small Table: favor Numeric Primary Keys (Integer or Long) for few million rows.
• Large Table: favor UUID if disk space allows for 10's of millions or billions rows.
• Generally avoid using Natural Primary Keys or Composite Primary Keys.

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Auto Incremented Primary Key

First, use @GeneratedValue(strategy = GenerationType.IDENTITY) annotation to class:

public class Author {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    ...

Then add V4__autoincrement_pk.sql for Flyway migrations:

alter table book change id id BIGINT auto_increment;
alter table author change id id BIGINT auto_increment;

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Vendor Specific Flyway Migrations

In the previous seciton, the V4__autoincrement_pk.sql works fine for MySQL, but it doesn't work with H2 Database. To solve this problem, we're going to setup for the vendor-specific migrations:

1. Edit application.properties and add spring.flyway.locations.

   spring.flyway.locations=classpath:db/migration/common,classpath:db/migration/{vendor}

2. Create directories for different database.
   • ./src/main/resources/db/migration/common
   • ./src/main/resources/db/migration/h2
3. Add V4.1__h2_auto.sql for H2 database:

   drop table if exists book;
   drop table if exists author;
   
   create table book
   (
       id IDENTITY not null,
       isbn      varchar(255),
       publisher varchar(255),
       title     varchar(255),
       author_id BIGINT,
       primary key (id)
   );
   
   create table author
   (
       id IDENTITY not null,
       first_name varchar(255),
       last_name  varchar(255),
       primary key (id)
   );

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UUID Primary Key

@Entity
public class AuthorUuid {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Type(type = "org.hibernate.type.UUIDCharType")
    @Column(length = 36, columnDefinition = "varchar(36)", updatable = false, nullable = false)
    private UUID id;
    ...
}

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UUID RFC 4122 Primary Key

@Entity
public class BookUuid {
    @Id
    @GeneratedValue(generator = "uuid2")
    @GenericGenerator(name = "uuid2", strategy = "uuid2")
    @Column(columnDefinition = "BINARY(16)", updatable = false, nullable = false)
    private UUID id;
    ...
}

To deal with the Hibernate and H2 Database UUID validation error, we should use "VARBINARY(16)" instead of "BINARY(16)".

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Natural Primary Key

@Entity
public class BookNatural {
    @Id
    private String title;
    private String isbn;
    private String publisher;
    ...
}

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Composite Primary Key

@Entity
@IdClass(NameId.class)
public class AuthorComposite {
    @Id
    private String firstName;

    @Id
    private String lastName;
    private String country;
    ...
}

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Embedded Composite Primary key

@Entity
@Table(name = "author_composite")
public class AuthorEmbedded {
    @EmbeddedId
    private NameId nameId;

    private String country;
    ...
}

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