I'm using JPA to store an Entity that has a creation date. I want to select a single Entity per date. I don't care which one, just one for each creation date. I've been trying sub-select clauses but i can't get them to work. Does anyone have any ideas?
Essentially I have the following Entity:
@Entity
class E {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
public Long id;
@Temporal(TemporalType.DATE)
private Date creationDate;
}
I want to select the following from the table:
ID DATE
1 3/4/5 <-- SELECT
2 3/4/5
3 4/4/5 <-- SELECT
4 5/4/5 <-- SELECT
5 5/4/5
6 5/4/5
As a work around i'm selecting the dates "SELECT DISTINCT(e.creationDate) ..." and then selecting the entities for each date, but there doesn't seem to be a LIMIT ??? so i'm basically having to select the entire table.
You can override the equals()
method of your class E
to return true on equals dates. And with this in place, put all your entities fetched from the DB without any constraint into a Set
. The set will take care of eliminating duplicates for you based on the date(since your equals method was written in such a way).
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