Hibernate tricks that even Java developers don’t know

Tram Ho


Hibernate is an open source ORM (Object Relational Mapping) library that helps programmers write Java applications that can map objects (pojo) with relational database management, and support implementation of programming concepts. object-oriented program with relational data. In short, Hibernate will be an intermediate layer between the application and the database, and we will communicate with Hibernate instead of communicating with the database. This article will not cover hibernate configurations but will show the benefits of hibernate that Java Developer itself does not know.


Use UUID as a primary key in Hibernate

Problem: You want to use the UUID as a primary key in the database.

Solution :

Hibernate has very good support for the properties of type java.util.UUID to use the UUID as the primary key and provides two generators for generating UUIDs. Hibernate supports 2 main types IETF RFC 4122 version 4 and IETF RFC 4122 version 1. Here I only introduce to create according to RFC 4122 standard version 4

ETF RFC 4122 version 4.

To be able to create UUDI, we just need to add the @GeneratedValue annotation to the java.util.UUID primary key attribute. For example

When saving the object to the databae, a UUID will be created before the object is saved to the database

Map enum to database column

Problem: You want to map the enum property to columns in the database.

Solution: JPA and Hibernate provide two standard options for mapping enum to the column database. You can use Enum as String or in order

  • For Enum as String, renaming an enum value requires us to also update the database
  • For ordinal type: The order of an enum value depends on its position in the enum declaration. You will have to update your database when you delete existing values ​​or change the location of enum values. When performing the mapping, Hibernate and JPA support a comment so you can define the mapping type. with @Enumerated annotation

For example, a basic enum with an Enum is called AuthorStatus

. For the example below, use the @Enumerated annotation with ordinal type. If the default @Enumerated annotation is not declared or EnumType is not specified, Hibernate will use the default ordinal as the default mapping.

When performing Author saving to database with PUBLISHED status, Hibernate will store the value 0 into the database

If using the type ** STRING **, we need to declare the @Enumerated annotation and define the mapping type as EnumType.STRING

When Hibernate saves the Author into the database, Hibernate will save the PUBLISHED value to the database in the status column

Automatically set an attribute before saving

Problem : You want to automatically set an attribute before it is saved to the database: For example, time, calculating a value … Solution :: You can use the @PrePersist annotation to automatically set a price before it is saved in the database

Hibernate will call this method before it saves the Author into the database.

Hibernate calls the initizeCreatedAt method before it selects the primary key value from the database. It will then save the createdAt value to the database.

Calculate the properties of an object with the @Formula annotation in hibernate

Problem : The value of one of the entity’s attributes needs to be calculated using the SQL expression. And you want to map it with hibernate.

Solution : The @Formula annotation can be used to declare values ​​in the SQL snippet. Hibernate will execute it when performing queries from the database.

The following example uses the @Formula annotation to calculate the Author’s ages

When Hibernate fetches the Entity Author from the database, it adds the SQL excerpt of the @Formula annotation to its SQL statement.

Query query results as Stream in Java 8

Problem : You want to use Java 8 Stream to access the results Solution : For Hibernate 5.2 version, we can do that by using: Hibernate’s Query interface. It returns query results as Stream and uses HibernateScrollableResults to access the results. For example :


The above article is only a small part of the tips for you to work more effectively with Hibernate. There are many tricks I have not yet mentioned in this article. See you in the next posts

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Source : Viblo