使用 Criteria Builder API 自定义查询加入 JPA

Question

Currently I am doing it like this:

List<Table1Entity> findAllMatchingEntities(Table1Entity table1Entity) {
    String queryString = "SELECT table1.* FROM table1 " 
                    + "JOIN table2 t2 ON table1.id=t2.table1_id";

    if (table1Entity.getName() != null) {
          queryString +=" where name like ?";                 
    }

    Query query = em.createNativeQuery(queryString, Table1Entity.class);

    if (table1Entity.getName() != null) {
        query.setParameter(1, table1Entity.getName())    
    }

    return query.getResultedList();
}

If I want to check more parameters in this join this will quickly turn into a lot of if statements and it would be really complicated to set parameters correctly.

I know I can check parameters with criteria Builder API like this:

if(table1Entity.getName() != null) {
    table1EntitySpecification = (root, query, criteriaBuilder)
                         -> criteriaBuilder.like(
                            criteriaBuilder.lower(root
                           .get("name")),
                           ("%" + table1Entity.getName() + "%")
                           .toLowerCase());;
}

and after that get them all with:

findAll(table1EntitySpecification) with findAll from simpleJPARepository . Now I can chain them together with .or or .and etc. and avoid setting the parameter and checking for null second time.

But how do I do join with criteria APi ?

I know I can have in my @Repository something like this:

@Query(value = "SELECT table1.* FROM table1 JOIN table2 t2 ON table1.id=t2.table1_id", nativeQuery = true)
List<Table1Entity> findAllMatchingEntities(Table1Entity table1Entity);

But since name is optional (can be null ) I can't just leave it in @Query .

What is the best solution here to avoid using native query and in case of having to check many parameters to avoid using if statements?

Answer 1

I don't know if I fully get your question, but regarding the possibility of nulls, and using the CRUD repository, you can always do a null check before like:

@Query(value = "SELECT table1.* FROM table1 JOIN table2 t2 ON table1.id=t2.table1_id WHERE table1.id is not null", nativeQuery = true)
List<Table1Entity> findAllMatchingEntities(Table1Entity table1Entity);

Depending on what you are trying to achieve, you can always compose the query with similar checks like (not related to your code):

@Query("SELECT c FROM Certificate c WHERE (:id is null or upper(c.id) = :id) "
           + "and (:name is null or upper(c.name) = :name)")
List<Table1> findStuff(@Param("id") String id,
                       @Param("name") String name);