Custom query methods by naming convention in Spring Boot

Introduction

Custom query methods let you find data easily without writing SQL. You just name the method to tell Spring Boot what to search for.

You want to get users by their email address.

You need to find products cheaper than a certain price.

You want to list orders placed after a specific date.

You want to check if a record exists with a certain name.

You want to count how many items belong to a category.

Syntax

Spring Boot

List<Entity> findByPropertyName(Type value);
Optional<Entity> findByPropertyName(Type value);
boolean existsByPropertyName(Type value);
long countByPropertyName(Type value);
List<Entity> findByPropertyNameAndOtherProperty(Type value1, Type value2);

Method names start with findBy, existsBy, or countBy.

Use And, Or to combine conditions in method names.

Examples

Finds all users with the given last name.

Spring Boot

List<User> findByLastName(String lastName);

Finds a user by email, returns empty if none found.

Spring Boot

Optional<User> findByEmail(String email);

Checks if a user exists with the given username.

Spring Boot

boolean existsByUsername(String username);

Finds products cheaper than the given price.

Spring Boot

List<Product> findByPriceLessThan(Double price);

Sample Program

This example shows a Spring Data JPA repository with custom query methods named by convention. The service class calls these methods and prints results.

Spring Boot

package com.example.demo.repository;

import com.example.demo.model.User;
import org.springframework.data.jpa.repository.JpaRepository;
import java.util.List;
import java.util.Optional;

public interface UserRepository extends JpaRepository<User, Long> {
    List<User> findByLastName(String lastName);
    Optional<User> findByEmail(String email);
    boolean existsByUsername(String username);
}

// Sample usage in a service class
package com.example.demo.service;

import com.example.demo.model.User;
import com.example.demo.repository.UserRepository;
import org.springframework.stereotype.Service;
import java.util.List;
import java.util.Optional;

@Service
public class UserService {
    private final UserRepository userRepository;

    public UserService(UserRepository userRepository) {
        this.userRepository = userRepository;
    }

    public void demoQueries() {
        List<User> smiths = userRepository.findByLastName("Smith");
        System.out.println("Users with last name Smith: " + smiths.size());

        Optional<User> userOpt = userRepository.findByEmail("[e-mail]");
        System.out.println("User with email [e-mail] found: " + userOpt.isPresent());

        boolean exists = userRepository.existsByUsername("alice123");
        System.out.println("User with username alice123 exists: " + exists);
    }
}

Important Notes

Spring Boot creates the query automatically based on method name.

Make sure property names in method match entity field names exactly.

Use Optional return type when you expect zero or one result.

Summary

Custom query methods let you search data by naming methods clearly.

Use prefixes like findBy, existsBy, countBy.

Combine conditions with And or Or in method names.

Practice

1. What does a Spring Data JPA method named findByLastName do?

easy

A. Counts records where the lastName matches the given value

B. Deletes records where the lastName matches the given value

C. Checks if any record exists with the given lastName

D. Finds all records where the lastName matches the given value

Solution

1. Step 1: Understand the method prefix

   The prefix findBy in Spring Data JPA means it will search and return matching records.

2. Step 2: Analyze the property name

   The method uses LastName as the property to filter by, so it finds records with that lastName.

3. Final Answer:

   Finds all records where the lastName matches the given value -> Option D

4. Quick Check:

   findBy + property = find matching records [OK]

Hint: findBy means search and return matching records [OK]

Common Mistakes:

• Confusing findBy with deleteBy or countBy
• Thinking it returns a boolean instead of records
• Ignoring the property name after findBy

2. Which of the following is the correct syntax for a method that counts users by their age in Spring Data JPA?

easy

A. findCountByAge(int age);

B. countUsersByAge(int age);

C. countByAge(int age);

D. countAgeBy(int age);

Solution

1. Step 1: Identify the correct prefix for counting

   The correct prefix to count records is countBy.

2. Step 2: Check method naming pattern

   The method should be countByAge to count users filtered by age.

3. Final Answer:

   countByAge(int age); -> Option C

4. Quick Check:

   countBy + property = count matching records [OK]

Hint: Use countBy + property to count records [OK]

Common Mistakes:

• Adding extra words like Users in method name
• Using findCountBy which is invalid
• Placing property name after count instead of after By

3. Given the method existsByEmailAndStatus(String email, String status), what will it return if a user with email "[e-mail]" and status "active" exists?

medium

A. A list of users matching the email and status

B. true

C. false

D. The count of users matching the email and status

Solution

1. Step 1: Understand the method prefix

   The prefix existsBy returns a boolean indicating if any record matches the criteria.

2. Step 2: Analyze the condition

   The method checks if a user exists with the given email and status combined with And.

3. Final Answer:

   true -> Option B

4. Quick Check:

   existsBy + conditions returns boolean [OK]

Hint: existsBy returns true if matching record exists [OK]

Common Mistakes:

• Expecting a list instead of boolean
• Confusing existsBy with findBy
• Ignoring the combined conditions with And

4. Identify the error in this Spring Data JPA method declaration: List<User> findByNameOr(int age, String name);

medium

A. The method name is missing the property after 'Or'

B. The method should use 'And' instead of 'Or' for combining conditions

C. The order of parameters does not match the method name conditions

D. The return type should be boolean for 'findBy' methods

Solution

1. Step 1: Analyze the method name structure

   The method name uses 'Or' but does not specify the property after 'Or'. It should be like 'findByNameOrAge'.

2. Step 2: Check parameter order and names

   Parameters should match the properties in the method name order, but the main error is missing property after 'Or'.

3. Final Answer:

   The method name is missing the property after 'Or' -> Option A

4. Quick Check:

   Method names must specify property after 'Or' [OK]

Hint: After 'Or' or 'And', always specify property name [OK]

Common Mistakes:

• Leaving out property name after 'Or' or 'And'
• Mixing parameter order with method name order
• Using wrong return type for findBy methods

5. You want to create a method that finds all orders where the customer's city is "New York" and the order total is greater than 100. Which method name correctly follows Spring Data JPA naming conventions?

hard

A. findByCustomerCityAndOrderTotalGreaterThan(String city, double total);

B. findOrdersByCityAndTotalGreater(String city, double total);

C. findByCityAndOrderTotalGreaterThan(String city, double total);

D. findByCustomerCityAndOrderTotalGreater(String city, double total);

Solution

1. Step 1: Identify the correct property names

   The properties are nested: customer.city and orderTotal. The method name must reflect this exactly.

2. Step 2: Use correct keywords for comparison

   For 'greater than', the keyword is 'GreaterThan' in Spring Data JPA method names.

3. Step 3: Combine conditions with 'And'

   The method name should combine both conditions with 'And' and use full property paths.

4. Final Answer:

   findByCustomerCityAndOrderTotalGreaterThan(String city, double total); -> Option A

5. Quick Check:

   Use full property names + GreaterThan + And [OK]

Hint: Use full property names and 'GreaterThan' for > comparisons [OK]

Common Mistakes:

• Using incomplete property names
• Using 'Greater' instead of 'GreaterThan'
• Omitting 'By' after 'find'