Hibernate：将mysql Query Datedif转换为HQL查询

Question

here is my Query in mysql

SELECT DATEDIFF('2008-11-30','2008-11-29') AS DiffDate

how to convert in to Hibernate Query Language

Answer 1

One of the way you can achieve this by extending mysql dialect and register it using registerFunction(String, SQLFunction)

public class CustomMySQL5InnoDBDialect extends MySQL5InnoDBDialect {

  public CustomMySQL5InnoDBDialect () {
    super();
    registerFunction( "datediff", new SQLFunctionTemplate( StandardBasicTypes.INTEGER, "datediff(?1, ?2)" ) );
 }

}

Answer 2

I do not think that you could get this specific mysql function into JPA/HQL (you can still use some native query if you want). A better approach would be using a third party library like [Joda-time][1] to compute the number of days between two dates. I do not really see why we should use the database for this.