Passing optional parameters to @Query of a Spring Data Repository method

问题

I work with Spring Data and Neo4j in my current project and have the following situation:

@RestController
@RequestMapping(value = SearchResource.URI)
public class PersonResource {

public static final String URI = "/person";

@Autowired
PersonRepository personRepository;

@GetMapping
public Collection<Person> findPersons(
    @RequestParam(value = "name", required = false) String name,
    @RequestParam(value = "birthDate", required = false) Long birthDate,
    @RequestParam(value = "town", required = false) Spring town) {

    Collection<Person> persons;

    if (name != null && birthDate == null && town == null) {
        persons = personRepository.findPersonByName(name);
    } else if (name != null && birthDate != null && town == null {
        persons = personRepository.findPersonByNameAndBirthDate(name, birthDate);
    } else if (name != null && birthDate != null && town != null {
        persons = personRepository.findPersonByNameAndBirthDateAndTown(name, birthDate, town);
    } else if (name == null && birthDate != null && town == null {
        persons = findPersonByBirthDate(birthDate);
    } else if
        ...
    }
    return persons;
}
}

You probably already can see my problem: the chain of if-else-blocks. Each time I add a new filter for searching for persons, I have to add new optional parameter, double all the if-else-blocks and add new find-Methods to my PersonRepository. All the find-Methods are annotated with Spring @Query annotation and get a custom cypher query to get the data.

Is it possible to implement this functionality in a more elegant way? Does Spring Data offer any support in such situation?

回答1:

I solved this problem using QueryDSL with Spring Data. There is a good tutorial on baeldung.com. With QueryDSL your spring data query is simply personRepository.findAll(predicate);.

You can use an object to represent the multiple request parameters and declare their type to be Optional<String> name; etc.

Then you can build the predicate (assuming you setup you stuff as in the linked tutorial):

Predicate predicate = new MyPredicateBuilder().with("name", ":", name.orElse(""))
.with("birthDate", ":", birthDate.orElse(""))
.with("town", ":", town.orElse(""))
.build();

I personally modified it so it didn't use the ":" as they are redundant for my usage.

来源：https://stackoverflow.com/questions/45716923/passing-optional-parameters-to-query-of-a-spring-data-repository-method