Specification pattern for dynamic queries in Spring Boot - Mini Project: Build & Apply

Specification Pattern for Dynamic Queries in Spring Boot

📖 Scenario: You are building a simple product catalog application. Users want to search products by different criteria like name, category, and price range. You will use the Specification pattern to create flexible and dynamic database queries in Spring Boot.

🎯 Goal: Build a Spring Boot Specification to filter products dynamically based on user search criteria.

📋 What You'll Learn

Create a Product entity with fields: id, name, category, price

Create a Specification class to build dynamic queries

Use Specification to filter products by name, category, and price range

Combine multiple Specifications to handle multiple filters

💡 Why This Matters

🌍 Real World

Many applications need to filter data based on user input. The Specification pattern helps build flexible and reusable queries without writing many fixed methods.

💼 Career

Understanding dynamic queries with Specifications is valuable for backend developers working with Spring Boot and databases.

1

Create the Product entity

Create a Java class called Product with fields Long id, String name, String category, and Double price. Use @Entity and @Id annotations for JPA.

Spring Boot

// Your code here

Need a hint?

Use @Entity above the class and @Id on the id field.

2

Create the ProductSpecification class

Create a class called ProductSpecification that implements Specification<Product>. Add a private field SearchCriteria criteria and a constructor to set it.

Spring Boot

import org.springframework.data.jpa.domain.Specification;

// Your code here

Need a hint?

Implement Specification<Product> and add a constructor that takes SearchCriteria.

3

Implement the toPredicate method for dynamic filtering

In ProductSpecification, implement the toPredicate method. Use criteria.getOperation() to check if it is : for equality or > or < for price comparisons. Return the appropriate Predicate using builder.equal, builder.greaterThanOrEqualTo, or builder.lessThanOrEqualTo.

Spring Boot

    @Override
    public javax.persistence.criteria.Predicate toPredicate(javax.persistence.criteria.Root root,
            javax.persistence.criteria.CriteriaQuery query,
            javax.persistence.criteria.CriteriaBuilder builder) {
        // Your code here
    }

Need a hint?

Use a switch on criteria.getOperation() and return the correct Predicate for each case.

4

Combine Specifications for dynamic queries

In a service or repository method, create multiple ProductSpecification instances for name, category, and price range. Combine them using Specification.where() and and() methods to build a dynamic query.

Spring Boot

// Your code here to combine specifications

Need a hint?

Start with Specification.where(null) and add filters with and() if values are not null.