Spring data JPA and parameters that can be null

问题:

My understanding is, that with Spring data JPA I cannot have a query method to fetch all rows where a column equals a given non-null method parameter and use the same method to fetch all rows where this column is NULL when the method parameter is null.

Is that correct?

So I have to distinguish this in my JAVA code and I must use a separate query method explicitly asking for null values, like in the example below?

// Query methods
List<Something> findByParameter(Parameter parameter);
List<Something> findByParameterIsNull();

...

List<Something> result = new ArrayList<>();

if (parameter == null)
  result = findByParameterIsNull();
else
  result = findByParameter(parameter);

That's bad, if I have 4 parameters which could be null and would have to code 16 different query methods.

回答1:

You are right.

A request has been made to support better handling of null parameters. https://jira.spring.io/browse/DATAJPA-121

In your case, i would advise you to write your repository implementation and to use a custom CriteriaQuery to handle your case.

Also you can use the @Query annotation with the is null syntax :

@Query("[...] where :parameter is null"
public List<Something> getSomethingWithNullParameter();

EDIT

Since Spring data jpa 2.0, spring now supports @Nullable annotation. This can be helpful to handle null parameters passed.

From the documentation :

@Nullable – to be used on a parameter or return value that can be null.

回答2:

It seems Query by Example might be what you need.

Query by Example is a new feature in Spring Data (since version Hopper, out April 2016), which allows one to create simple dynamic queries with a code like this

Person person = new Person();                          
person.setFirstname("Dave");                           

ExampleMatcher matcher = ExampleMatcher.matching()     
  .withIncludeNullValues();                        

Example<Person> example = Example.of(person, matcher);

personRepository.count(example);
personRepository.findOne(example);
personRepository.findAll(example);

Methods count/findOne/findAll that take an instance of org.springframework.data.domain.Example as a parameter (and some of them also take sorting/pagination parameters) are coming from org.springframework.data.repository.query.QueryByExampleExecutor<T> interface, which is extended by org.springframework.data.jpa.repository.JpaRepository<T, ID extends Serializable> interface.

In short, all JpaRepository instances now have these methods.

回答3:

i found something...if u put the parameter in the jpa method like this

@Param("value") String value,

then it can be null and in the query you will have this condition:

(table.value = :value OR :value IS NULL)

if the value is null it will automatically return true and if is not null, it will search that value in the table.

回答4:

Today as of Jun 2018, by looking at https://jira.spring.io/browse/DATAJPA-121, the query will automatically form is null if your parameter is null.

I did that in my project, it is true:

compile group: 'org.springframework.data', name: 'spring-data-jpa', version: '2.0.7.RELEASE'

--

public interface AccountDao extends CrudRepository<T, ID> {

    //this can accept null and it will become isNull
    public List<MyAccount> findByEmail(String email);

}

if parameter is null:

select
        myaccount0_.id as id1_0_,
        myaccount0_.email as email2_0_,
        myaccount0_.password as password3_0_,
        myaccount0_.user_id as user_id4_0_ 
    from
        my_account myaccount0_ 
    where
        myaccount0_.email is null

if parameter is not null:

select
        myaccount0_.id as id1_0_,
        myaccount0_.email as email2_0_,
        myaccount0_.password as password3_0_,
        myaccount0_.user_id as user_id4_0_ 
    from
        my_account myaccount0_ 
    where
        myaccount0_.email=?
11:02:41.623 [qtp1507181879-72] TRACE o.h.type.descriptor.sql.BasicBinder - binding parameter [1] as [VARCHAR] - [[e-mail]] 

Then it comes to an interesting question, some developers want better control to ignore the parameter in query if it is null, this is still being under investigating in https://jira.spring.io/browse/DATAJPA-209.