我如何仅从JPQL中的日期时间字段按日期分组

Question

For mysql I wrote a query like

SELECT * FROM mytable GROUP BY DATE(dateTimeField)

But i can't use the DATE() function in JPQL. Anyone have an idea how to resolve this problem?

Answer 1

If You use Hibernate under the hood you can try :

1. Create your own dialect with custom function

    public class CustomPostgresqlDialect extends PostgreSQLDialect { public CustomPostgresqlDialect() { super(); registerFunction("truncate_date", new SQLFunctionTemplate( StandardBasicTypes.TIMESTAMP, "DATE(?1)" )); } } 

2. Register Your dialect in persistence.xml

    <property name="hibernate.dialect" value="my.own.CustomPostgresqlDialect"/> 

3. Use your function in JPQL.

    select p from Post p group by truncate_date(p.dateCreated) 

Answer 2

For Hibernate:

Suggestion 1:

Use cast(dateTimeField as date) . See here .

Suggestion 2:

You can try to concatenate year , month and year HQL expressions .

Take a look at line 360 of this testcase .

str(year(current_date))||'-'||str(month(current_date))||'-'||str(day(current_date))

But take the time to see the generated SQL, it may (and probably will be) ugly and slow.

Answer 3

If you are using EclipseLink you can use the FUNC() function in JPQL to call a specific database function:

Support for Native Database Functions Using FUNC

Answer 4

I'm afraid that's beyond the scope of what JPQL offers. You will have to resort to native queries.

Here's the List of available functions in JPQL:

Java EE Tutorial 6 > Persistence > JPQL > Functional Expressions