How to pass an argument to a function when using ParameterExpression together with org.springframework.data.jpa.domain.Specification?

问题

I am using org.springframework.data.jpa.domain.Specification together with JpaSpecificationExecutor to easily create queries with conditions in Java but now I need to call a MySQL DB function that returns an integer value.

The problem is that it is unclear how to pass an argument for this function as I am not using TypedQuery:

// cb here is CriteriaBuilder
ParameterExpression param = cb.parameter(String.class);

Predicate predicate = cb.greaterThan(cb.function("A_FUNCTION", 
      Integer.class, param), 0);

Specification spec = cb.and(predicate);

// query is executed like this

return (int) repositoryThatExtendsJpaSpecificationExecutor.count(test);

And the example from here is not helping.

回答1:

I think what you really need is a literal which you can create using CriteriaBuilder.literal. A full example would look like

// cb here is CriteriaBuilder
Expression param = cb.literal("Stephen Hawking");

Predicate predicate = cb.greaterThan(cb.function("A_FUNCTION", 
      Integer.class, param), 0);

Specification spec = cb.and(predicate);

If the value doesn't come from your application you can use (m)any of the functions returning an Expression.

来源：https://stackoverflow.com/questions/49304067/how-to-pass-an-argument-to-a-function-when-using-parameterexpression-together-wi