Is it possible to generate a dynamic SQL query in spring boot?

Question

I want to implement a search function with five optional variables and in every combination, so a switch/case is not a possible way. So i can't use the build in spring boot functions, because they are not dynamic (correct me if i'm wrong). I know there is the @query annotation in the crudrepository, but there is no way to write a query with optional parameters? I tried to write my own database access with jpa, without the help of spring boot CrudRepository. I read in the manual this should work:

@Autowired
@PersistenceContext
private EntityManager em;

@Transactional
public List<Persons>searchPersons(params...){}

But here is the problem, my EntityManager is always null and i have no idea why. I searched some hours and found nothing.

Maybe you guys know a way to write a dynamic SQL query in Spring Boot. Is there a way in the CrudRepository to define optional parameters for the query? Btw i use a postgreSQL database.

Many thanks for your help.

Answer 1

You might want to have a look at Specifications.

See the documentation here

For that to work, your repository interface needs to implement JpaSpecificationExecutor .

Answer 2

You can use a custom repository (create your own interface, write one Impl class for it and extend your repository by that interface.

You should then have:

PersonRepositoryCustom

PersonRepositoryCustomImpl

Next, you implement a query, using the EntityManager autowired into your repository. You can do this by using JPQL or the JPA 2.1 Criteria API.

For each parameter, have a condition to add it to the query itself, as well as the prepared statement parameters. That way, you can build a dynamic query.

The following thread is related: Best way to create JPA query that might contain a parameter or might not

Answer 3

I know this question is old but to anyone coming here interested in implementing dynamic SQL queries , check out these two blog posts, they are great.

1. Implementing dynamic SQL queries using Spring Data JPA Specification and Criteria API
2. Writing dynamic SQL queries using Spring Data JPA repositories and EntityManager