如何转换 JPA 标准表达式<long>长 java 型</long>

Question

. Answers to this question are eligible for a +50 reputation bounty. Shadyar wants to to this question.

This code

    criteriaBuilder.literal(LocalDateTime.now().minusDays( (long) root.get("person").get("birthDay").as(Long.class)))  

has not compile error but at run time gets this error:
Cannot cast from Expression to int

I tried using String:

    criteriaBuilder.literal(LocalDateTime.now().minusDays( Long.parseValue( root.get("person").get("birthDay").toString())))  

This also gets error:
ERROR: For input string: "org.hibernate.query.criteria.internal.path.SingularAttributePath@2ed2d35d"; nested exception is java.lang.NumberFormatException: For input string: "org.hibernate.query.criteria.internal.path.SingularAttributePath@2ed2d35d"

Answer 1

I think you are mixing different concepts.

Please, be aware that when using the JPA related artifacts is important to understand that they are objects that define expressions that may represent, when computed, a certain value of a certain type in the database, but when you are constructing your JPA criteria queries, they are just that, artifacts for your JPA criteria queries.

Now consider the following expression you are trying using:

root.get("person").get("birthDay").toString()

As a result of the evaluation of this code you will get a String representation of the JPA criteria path you are defining, org.hibernate.query.criteria.internal.path.SingularAttributePath@2ed2d35d in your use case.

Then, if you compute Long.parseValue of org.hibernate.query.criteria.internal.path.SingularAttributePath@2ed2d35d if will raise an error because org.hibernate.query.criteria.internal.path.SingularAttributePath@2ed2d35d doesn't represent a valid number.

It is unclear by your question what you are actually trying to achieve but the JPA criteria API provides a rich set of builtin expressions you can use as Predicate s to deal with dates, such as, assuming root.get("person").get("birthDay") represent a Date like object:

cb.greaterThanOrEqualTo(root.get("person").get("birthDay"), cb.literal(LocalDate.now()));
//...
cb.greaterThan(root.get("person").get("birthDay"), cb.literal(LocalDate.now()));
//...
cb.lessThanOrEqualTo(root.get("person").get("birthDay"), cb.literal(LocalDate.now()));
//...
cb.lessThan(root.get("person").get("birthDay"), cb.literal(LocalDate.now()));

You can create your own function using cb.function as well and use that function in your predicates. Consider for that purpose defining a helper method somewhere in your code, for example:

public static Expression<Long> daysBetween(
  CriteriaBuilder cb, Expression<LocalDate> startDate, Expression<LocalDate> endDate) {
  return cb.function("DAYS_BETWEEN", long.class, startDate, endDate);
}

Where DAYS_BETWEEN is the name, you can choose the one you consider most appropriate, of a database level predefined or user defined function. In Oracle for example it exists per se , but it should be straight forward to implement in other database systems:

create or replace function days_between...

Then, use this helper method in your code. For example, give me the persons that turns years in the following 10 days :

cb.and(
  cb.lessThan(
    daysBetween(cb, root.get("person").get("birthDay"), cb.literal(LocalDate.now()) ),
    cb.literal(10)
  )
)

Answer 2

I haven't used this, I found the relevant documentation, I think it seems to be available like the following, just to provide a reference, I hope it can help you.

literal(T)

Integer a = 1;
Long b = 2L;
String c = "3";
Expression<Integer> integerParameter = criteriaBuilder.literal(a);
Expression<Long> longParameter = criteriaBuilder.literal(b);
Expression<String> stringParameter = criteriaBuilder.literal(c);

And i found that method minusDays(long) return a LocalDateTime , so i think we should take that like:

LocalDateTime ldt = LocalDateTime.now().minusDays( (long) root.get("person").get("birthDay").as(Long.class));
Expression<LocalDateTime> longParameter = criteriaBuilder.literal(ldt);

As for how to convert LocalDateTime into the data you need, I am currently unclear, because it is not clear what your specific needs are.

Answer 3

Point is here. Look at the error message,maybe it is not Long.

java.lang.NumberFormatException: For input string: "org.hibernate.query.criteria.internal.path.SingularAttributePath@2ed2d35d"

Please check value for

root.get("person").get("birthDay")