Spring Data JPA – Top and First

I like Spring Data JPA. It helps simplify my codebase, and most of the time frees me up from writing JPAQL or SQL. I’m also impressed by the complexity of query you can write using Spring Data. My favourite feature is returning the first or top records from a table

Lets say I have a table tracking document versions –

DOCUMENT_TABLE

DOCUMENT_ID NAME VERSION
1 mydoc.doc 1
2 mydoc.doc 2
3 mydoc.doc 3

 
With its associated JPA object –

[sourcecode lang=”java”] @Entity
@Table(name = "DOCUMENT_TABLE")
public class Document implements Serializable {
private static final long serialVersionUID = 1L;

@Id
@Column(name = "DOCUMENT_ID")
private Long documentId;

@Basic(optional = false)
@NotNull
private String name;

@Basic(optional = false)
@NotNull
private Long version;

}
[/sourcecode]

My SQL would be –

[sourcecode lang=”sql”] SELECT *
FROM
(SELECT *
FROM document_table dt
WHERE dt.name = ‘mydoc.doc’
ORDER BY dt.VERSION DESC
)
WHERE rownum = 1;
[/sourcecode]

Or in JPA –
[sourcecode lang=”sql”] select d
from Document d
where d.name = :name
and d.version = (select max(d.version) from Document d where d.name = :name)
[/sourcecode]

But I want to keep my codebase consistent so the first thing I can try is –

[sourcecode lang=”java”] public interface DocumentRepository extends CrudRepository<Document, Long> {
List<Document> findByNameOrderByVersionDesc(String name);
}
[/sourcecode]

I can get the first record –

[sourcecode lang=”java”] List<Document> documentList =
documentRepository.findByNameOrderByVersionDesc("mydoc.doc");
Document document = documentList.get(0);
[/sourcecode]

Thats Ok I guess. Another alternative is to have a straight SQL query in the repository, but the best option is to use the Top feature in spring data –

[sourcecode lang=”java”] public interface DocumentRepository extends CrudRepository<Document, Long> {
Document findFirstByNameOrderByVersionDesc(String name);
Document findTopByNameOrderByVersionDesc(String name);
}
[/sourcecode]

The above methods are equivalent

We can even use Top to return the top n records –

[sourcecode lang=”java”] Document findTop2ByNameOrderByVersionDesc(String name);
[/sourcecode]

Interestingly the underlying SQL generated by Spring Data opts for the rownum construct I used in my original SQL statement

About the Author Martin Farrell

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