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Spring Data: Bridging Multiple Databases

Querydsl Extension

Understand how Querydsl integrates with Spring Data to create type-safe, readable queries. Learn to set up dependencies, generate query classes, use Predicate executors, and utilize JPAQueryFactory for direct database access, enhancing query maintainability and clarity.

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Querydsl is a Java framework to create database queries that are type-safe, similar to SQL, and easy to read and implement.

Querydsl dependencies in build.gradle

First, let’s add the dependencies to the build.gradle file to add Querydsl support to our Spring Data project.

TypeScript 4.9.5
plugins {
    id 'java'
    id 'org.springframework.boot' version '3.0.2'
    id 'io.spring.dependency-management' version '1.1.0'
}
group = 'com.smartdiscover'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = '17'
repositories {
    mavenCentral()
}
dependencies {
    implementation 'org.springframework.boot:spring-boot-starter-data-jpa'
    implementation 'org.projectlombok:lombok:1.18.26'
    annotationProcessor 'org.projectlombok:lombok'
    runtimeOnly 'com.h2database:h2'
    
    implementation "com.querydsl:querydsl-core:5.0.0"
    implementation 'com.querydsl:querydsl-jpa:5.0.0:jakarta'
    annotationProcessor 'com.querydsl:querydsl-apt:5.0.0:jakarta'
    annotationProcessor "jakarta.persistence:jakarta.persistence-api"
}

Explanation:

  • Lines 21 and 22: We add the querydsl-core and querydsl-jpa dependencies along with the jakarta API support.
  • Lines 23 and 24: We set the annotation processorAnnotation processors in Gradle build automatic code generation and perform tasks based on annotations present in the source code, enhancing project functionality. for querydsl-apt and jakarta.persistence-api.

So, when we build our Spring Data application using Gradle’s build command, Querydsl will scan for the classes annotated with the @Entity annotation and automatically generate the query classes for them.

In our project, it’ll automatically create the QCustomer query class with references to the properties of the Customer class.

Java
package com.smartdiscover.entity;
public class QCustomer extends EntityPathBase<Customer> {
    private static final long serialVersionUID = 1828420791L;
    public static final QCustomer customer = new QCustomer("customer");
    public final StringPath firstName = this.createString("firstName");
    public final NumberPath<Long> id = this.createNumber("id", Long.class);
    public final StringPath lastName = this.createString("lastName");
    // constructors
}
...