Spring Data JPA Query Method - Distinct

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In this tutorial, we will learn how to write a query method for distinct results in the Spring Data JPA repository.

JPA query methods are the most powerful methods, we can create query methods to select the records from the database without writing SQL queries. Behind the scenes, Spring Data JPA will create SQL queries based on the query method and execute the query for us.

Let's follow the Spring Data JPA naming convention to write a query method distinct for the Product entity class.

We need to create a method starting with prefix find followed by Distinct and then field name - 

findDistinct[FieldName]

Example: Consider the following Product entity class and if we want to retrieve a distinct product by its name field then here is the Spring Data JPA query method:

public Product findDistinctByName(String title);

Let's create a complete example to understand end-to-end.

Maven Dependencies

Add the following maven dependencies to your Spring Boot project:

<dependency>	<groupId>org.springframework.boot</groupId>	<artifactId>spring-boot-starter-data-jpa</artifactId>	</dependency>	<dependency>	<groupId>com.mysql</groupId>	<artifactId>mysql-connector-j</artifactId>	<scope>runtime</scope>	</dependency>

Product Entity

Let's first create a Product entity class and add the following content to it:

package net.javaguides.springdatajpacourse.entity; import org.hibernate.annotations.CreationTimestamp; import org.hibernate.annotations.UpdateTimestamp; import jakarta.persistence.*; import java.math.BigDecimal; import java.util.Date; @Entity @Table(name="products") public class Product { @Id @GeneratedValue(strategy = GenerationType.IDENTITY) @Column(name = "id") private Long id; @Column(name = "sku") private String sku; @Column(name = "name") private String name; @Column(name = "description") private String description; @Column(name = "price") private BigDecimal price; @Column(name = "image_url") private String imageUrl; @Column(name = "active") private boolean active; @Column(name = "date_created") @CreationTimestamp private Date dateCreated; @Column(name = "last_updated") @UpdateTimestamp private Date lastUpdated; public Long getId() { return id; } public void setId(Long id) { this.id = id; } public String getSku() { return sku; } public void setSku(String sku) { this.sku = sku; } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getDescription() { return description; } public void setDescription(String description) { this.description = description; } public BigDecimal getPrice() { return price; } public void setPrice(BigDecimal price) { this.price = price; } public String getImageUrl() { return imageUrl; } public void setImageUrl(String imageUrl) { this.imageUrl = imageUrl; } public boolean isActive() { return active; } public void setActive(boolean active) { this.active = active; } public Date getDateCreated() { return dateCreated; } public void setDateCreated(Date dateCreated) { this.dateCreated = dateCreated; } public Date getLastUpdated() { return lastUpdated; } public void setLastUpdated(Date lastUpdated) { this.lastUpdated = lastUpdated; } @Override public String toString() { return "Product{" + "id=" + id + ", sku='" + sku + '\'' + ", name='" + name + '\'' + ", description='" + description + '\'' + ", price=" + price + ", imageUrl='" + imageUrl + '\'' + ", active=" + active + ", dateCreated=" + dateCreated + ", lastUpdated=" + lastUpdated + '}'; } }

ProductRepository

Let's create ProductRepository which extends JpaRepository and add the following code to it:

import net.javaguides.springdatajpacourse.entity.Product; import org.springframework.data.jpa.repository.JpaRepository; public interface ProductRepository extends JpaRepository<Product, Long> {	/** * Return the distinct product entries whose name is given as a method parameter * If no product entry is found, this method returns null. */	public Product findDistinctByName(String title); }

Note that the below query method returns the distinct product entity whose name is given as a method parameter. If no product entry is found, this method returns null.

public Product findDistinctByName(String title);

Configure MySQL and Hibernate Properties

Let's use the MySQL database to store and retrieve the data in this example and we gonna use Hibernate properties to create and drop tables.

Open the application.properties file and add the following configuration to it:

spring.datasource.url=jdbc:mysql://localhost:3306/ecommerce?useSSL=false spring.datasource.username=root spring.datasource.password=Mysql@123 spring.jpa.properties.hibernate.dialect = org.hibernate.dialect.MySQLDialect spring.jpa.hibernate.ddl-auto = create-drop spring.jpa.show-sql=true spring.jpa.properties.hibernate.format_sql=true

Make sure that you will create ecommerce database before running the Spring boot application.

Also, change the MySQL username and password as per your MySQL installation on your machine.

Testing Spring Data JPA Query Method - Distinct

In order to test the query method with distinct that we have created, we gonna use CommandLineRunner.run() method to execute the testing code while the Spring boot application startup: 

import net.javaguides.springdatajpacourse.entity.Product; import net.javaguides.springdatajpacourse.repository.ProductRepository; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.boot.CommandLineRunner; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; import java.math.BigDecimal; import java.util.Date; import java.util.List; @SpringBootApplication public class SpringDataJpaCourseApplication implements CommandLineRunner{	public static void main(String[] args) throws Exception {	SpringApplication.run(SpringDataJpaCourseApplication.class, args);	}	@Autowired	private ProductRepository productRepository;	@Override	public void run(String... args) throws Exception { Product product = new Product(); product.setName("product 1"); product.setDescription("product 1 desc"); product.setPrice(new BigDecimal(100)); product.setDateCreated(new Date()); product.setLastUpdated(new Date()); product.setSku("product 1 sku"); product.setActive(true); product.setImageUrl("product1.png"); // save product productRepository.save(product); Product product2 = new Product(); product2.setName("product 2"); product2.setDescription("product 2 desc"); product2.setPrice(new BigDecimal(200)); product2.setDateCreated(new Date()); product2.setLastUpdated(new Date()); product2.setSku("product 2 sku"); product2.setActive(true); product2.setImageUrl("product2.png"); // save product 2 productRepository.save(product2); // test query method with multiple parameters Product distinctProduct = productRepository.findDistinctByName("product 1");	} }

After finishing the Spring boot application, you can able to see Spring Data JPA (uses Hibernate as JPA provider) generated SQL statements in a console:

Hibernate: insert into products (active, date_created, description, image_url, last_updated, name, price, sku) values (?, ?, ?, ?, ?, ?, ?, ?) Hibernate: insert into products (active, date_created, description, image_url, last_updated, name, price, sku) values (?, ?, ?, ?, ?, ?, ?, ?) Hibernate:  select distinct product0_.id as id1_0_, product0_.active as active2_0_, product0_.date_created as date_cre3_0_, product0_.description as descript4_0_, product0_.image_url as image_ur5_0_, product0_.last_updated as last_upd6_0_, product0_.name as name7_0_, product0_.price as price8_0_, product0_.sku as sku9_0_ from products product0_ where product0_.name=?

Note that the below Distinct SQL query from the above output:

select distinct product0_.id as id1_0_, product0_.active as active2_0_, product0_.date_created as date_cre3_0_, product0_.description as descript4_0_, product0_.image_url as image_ur5_0_, product0_.last_updated as last_upd6_0_, product0_.name as name7_0_, product0_.price as price8_0_, product0_.sku as sku9_0_ from products product0_ where product0_.name=?

Related Spring Data JPA Query Method Tutorials

• Spring Data JPA Query Method - Multiple Fields
• Spring Data JPA Query Method - Distinct
• Spring Data JPA Query Method - Greater Than
• Spring Data JPA Query Method - Less Than
• Spring Data JPA Query Method - Between
• Spring Data JPA Query Method - Like
• Spring Data JPA Query Method - IN Clause

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