How do you create a derived query method in Spring Data JPA?

Table of Contents

Introduction

Spring Data JPA simplifies database interaction by automatically generating queries based on method names. Derived query methods are a powerful feature that allows developers to create custom queries without writing explicit JPQL or SQL. Instead, the method name is parsed to create the query automatically. This feature helps streamline the development process, saving time and reducing boilerplate code.

In this guide, we will explore how to create derived query methods in Spring Data JPA, their significance, and provide practical examples to demonstrate how they work.

What is a Derived Query Method in Spring Data JPA?

A derived query method in Spring Data JPA is a method in a repository interface whose name follows a specific naming convention. Based on the method name, Spring Data JPA automatically constructs a query to retrieve data from the database. These methods allow you to avoid manually writing JPQL or SQL queries for common operations like finding records by attributes, sorting, and more.

How Derived Query Methods Work

Spring Data JPA parses the method name to create a corresponding query. The naming convention follows a pattern of property names and operations that map to SQL or JPQL. The framework will try to map these method names to actual database queries, such as findBy, countBy, deleteBy, and others.

For example:

  • findBy — To retrieve data based on an attribute
  • countBy — To count records based on an attribute
  • deleteBy — To delete records based on an attribute

Spring Data JPA also supports logical operators (like And, Or) and relational operators (GreaterThan, LessThan, etc.).

Creating Derived Query Methods

Basic Example: Find an Entity by Attribute

One of the simplest derived query methods is finding an entity by a property. For instance, you can create a method to find an Employee by their email.

Example:

In this case, Spring Data JPA automatically generates a query like:

Example with Multiple Attributes: findBy

You can extend the method name to include multiple attributes to create more specific queries. For example, if you wanted to find employees by both firstName and lastName, you can create a method like:

Example:

Spring Data JPA will generate a query like:

Using Comparison Operators: GreaterThan, LessThan, etc.

Spring Data JPA supports comparison operators that can be used within derived query methods. For example, to find employees with a salary greater than a certain amount:

Example:

This will generate a query like:

Other supported operators include:

  • LessThan, LessThanEqual
  • GreaterThanEqual
  • Between

Using Like for Partial Matching

If you need to perform partial matching (for example, finding employees whose first name starts with a particular string), you can use the Like operator.

Example:

Spring Data JPA will generate a query with a LIKE condition:

This will match any employee whose firstName contains the specified value.

Using Or for Multiple Conditions

To create queries with logical OR conditions, you can use the Or keyword in the method name. For example, to find employees with either a specific email or a specific department:

Example:

This will generate the following query:

Sorting and Pagination with Derived Queries

You can also add Sort or Pageable to your derived query methods to retrieve results with sorting or pagination. Spring Data JPA will automatically convert the method signature to support pagination and sorting.

Example with Pagination:

This method will return a page of employees in the given department, allowing for pagination.

Example with Sorting:

This will return all employees in a specific department, sorted by salary in descending order.

Practical Examples

Example 1: Find Employees by Department and Age

If you need to find employees in a particular department whose age is greater than a specific value, you can create a derived query method like this:

Spring Data JPA will generate:

SELECT e FROM Employee e WHERE e.department = :department AND e.age > :age

Example 2: Count Employees by Department

To count the number of employees in a given department, you can create a countBy query method:

This will generate a query like:

Conclusion

Derived query methods in Spring Data JPA are a powerful feature that allows you to automatically generate queries based on method names. By following specific naming conventions, you can avoid writing boilerplate queries and focus on building your application logic. These methods support a wide range of operations, including searching by attributes, using comparison operators, sorting, and pagination. With the flexibility of Spring Data JPA’s derived queries, you can easily create custom queries for common use cases while keeping your code concise and maintainable.

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