如何在种子库中使用分组依据？

Question

I want to use Group By in Seedstack, to count lines and sum certain values.

eg : I have this table "employee" in database :

id  name    section value
----------------------------
1   Chun    DDE     5
2   Tom     DMD     8
3   Diana   DMD     18
4   Frisk   DDE     2
5   Laura   DVD     10
6   Chris   DMD     15

And I need something like this equivalent in SQL:

SELECT section, count(1) as staff, sum(value) as result FROM employee group by section;
    section staff   result
    ------------------------
    DDE     2       7
    DMD     3       41
    DVD     1       10

What is the best way to do this in seedstack ?

Answer 1

SeedStack does its relational db access through the JPA or the JDBC standards:

• JPA is a "higher level" API that Object-Relational Mapping (ORM).
• JDBC is a "lower level" API that allows to directly execute SQL.

I recommend you to go the JPA route. You can learn how to configure and use it with SeedStack here: http://seedstack.org/guides/jpa

When using the business framework, persistence operations are encapsulated in repositories that you need to extend to go beyond built-in abilities. In a method of your custom repository you can use the full JPA API by obtaining the JPA EntityManager interface with getEntityManager() .

As for the JPA equivalent to Group By, you have can use either the criteria API or the JPQL query language. You can read this for more information: https://www.objectdb.com/java/jpa/query/jpql/group .

If you have JPA working fine, you can repost a more specific question with the JPA tag (regardless of using SeedStack or not).