How to use Criteria Queries in Spring Boot Data Jpa Application

Question

I have an application that uses Spring Boot Data jpa . So far i am using a repository like this

public interface StudentRepository extends CrudRepos         


        

Answer 1

It's very complicated to create specifications using JPA Criteria because the API is very verbose and instrusive.

With the Lambda JDK 8, you can create high very typed-queries using simples predicates.

@Test
public void testSimpleSpec() {
    String expected = 
        "select e0.id, e0.name "
        + "from Customer e0 "
        + "where (e0.regionCode = :p0)";

    Consumer> regionCode1 = 
        q -> q.where(i -> i.getRegionCode()).eq(1L);

    NativeSQLResult result = new QueryBuilder()
        .from(Customer.class)
        .whereSpec(regionCode1)
        .select(i -> i.getId())
        .select(i -> i.getName())
        .to(new NativeSQL())
        ;
    String actual = result.sql();

    Assert.assertEquals(expected, actual);
    Assert.assertEquals(result.params().get("p0"), 1L);
}

You can isolate the conditions and to reuse in others queries, ie, specifications.

https://github.com/naskarlab/fluent-query

https://github.com/naskarlab/fluent-query-eclipselink