spring DAta JPA derived queries

When using Spring Data JPA, developers can use derived query methods to generate queries based on the name of the method. This approach eliminates the need for manually writing queries, reducing boilerplate code and increasing productivity.

Derived queries use a simple naming convention based on the method name, so developers can easily write them without having to learn a new query language. In this article, we'll explore how to use Spring Data JPA-derived query methods and provide examples of how they work.

Prerequisites

To follow this article, you'll need the following:

Java 11 or later
Spring Boot 2.5 or later
Spring Data JPA
An IDE (e.g. IntelliJ IDEA or Eclipse)

Setup

Create a new Spring Boot project using your favorite IDE. Make sure to include the Spring Data JPA dependency in your pom.xml file:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>

Derived Query Methods

Derived query methods use a naming convention that maps the method name to the query that should be generated. The basic syntax is as follows:

find[Entity]By[Property]

Here, [Entity] refers to the name of the entity you want to query, and [Property] is the name of a property of that entity. For example, if you have an entity called User with a property called email, you can generate a query to find all users with a specific email address like this:

List<User> findByEmail(String email);

This method will generate a query that looks like this:

SELECT * FROM users WHERE email = :email

If you want to query based on multiple properties, simply add more properties to the method name:

List<User> findByEmailAndFirstName(String email, String firstName);

This method will generate a query that looks like this:

SELECT * FROM users WHERE email = :email AND first_name = :firstName

You can also use operators like Like and Between in your method names:

List<User> findByEmailLike(String email);
List<User> findByCreatedDateBetween(LocalDateTime start, LocalDateTime end);

These methods will generate queries like this:

SELECT * FROM users WHERE email LIKE %:email%
SELECT * FROM users WHERE created_date BETWEEN :start AND :end

You can also use keywords like OrderBy and Top to control the order and number of results:

List<User> findByOrderByEmailAsc();
List<User> findTop10ByOrderByCreatedDateDesc();

These methods will generate queries like this:

SELECT * FROM users ORDER BY email ASC
SELECT * FROM users ORDER BY created_date DESC LIMIT 10

Conclusion

Spring Data JPA-derived query methods provide a simple and convenient way to generate queries without having to write SQL statements manually. By following a simple naming convention, developers can quickly generate complex queries that would otherwise require a lot of boilerplate code.