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Spring Data JPA – Top and First

I like Spring Data JPA. It helps simplify your codebase, and 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 Spring Data JPA feature is top and first, which returns the first or top records from a table

Spring Data JPA – Top and First

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 –

@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;
}

My SQL would be –

SELECT *
FROM
(SELECT *
FROM document_table dt
WHERE dt.name = 'mydoc.doc'
ORDER BY dt.VERSION DESC
)
WHERE rownum = 1;

Or in JPA –

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 -
[code]
public interface DocumentRepository extends CrudRepository<Document, Long> {
List<Document> findByNameOrderByVersionDesc(String name);
}
[/sourcecode]
I can get the first record -
[code]
List<Document> documentList =
documentRepository.findByNameOrderByVersionDesc("mydoc.doc");
Document document = documentList.get(0);

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 -

public interface DocumentRepository extends CrudRepository<Document, Long> {
Document findFirstByNameOrderByVersionDesc(String name);
Document findTopByNameOrderByVersionDesc(String name);
}

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

My name is Martin Farrell. I have almost 20 years Java experience. I specialize inthe Spring Framework and JEE. I’ve consulted to a range of businesses, and have provide Java and Spring mentoring and training. You can learn more at About

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