I have the following User entity:
public class User extends PanacheEntityBase{
#Id
#GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "DataIdGenerator")
#Column(name = "id")
public Long id;
public String name;
public String location;
public int age;
}
I also have the following endpoint: '/user', with a 'select' query parameter where you provide the column names you want to receive. It should be possible to select any combination of columns like: /user?select=id,name, /user?select=id,age, /user?select=name,age, /user?select=age,name
Based on the 'select' query I want to use a projection to get the selected columns only. Currently I'm using the query to create the following query fe: /user?select=id,name to SELECT d.id, d.name FROM User d, however I need the DTO to be dynamic based on the columns provided too.
Currently I have the following projection where UserDTO is a class with id and name attributes. This works fine, but if I change any parameter I need a different DTO.
// This variable is dynamically created based on query parameters
String query = 'SELECT d.id, d.name FROM User d'
return User.find(query).project(UserDTO.class).list();
Is it possible to make this projection DTO class more dynamic, so it supports all combinations?
I suspect the Panache API is not flexible enough at the moment to do what you are asking.
But you could use the Hibernate Reactive API without Panache:
#Inject
Mutiny.SessionFactory sf;
public Uni<List<Tuple>> find(String query) {
return sf.withSession(session ->
session.createQuery(query, Tuple.class).getResultList()
);
}
Once you have the Tuple, you can convert it to the type you prefer.
Related
I'm trying to write the following query using JPA Specification.
select distinct name from hcp where area = 'Dhaka';
select distinct name from hcp where area = 'Dhaka';
The hcp entity looks as following
#Entity
public class HCP implements Serializable {
#Id
#Column
private String id;
#Column
private String name;
#Column
private String area;
}
The table would look like this
I tried to convert the above query using jpa-specification as following. It's selecting 'name' field and I've set distinct as true
List<HCP> result = hcpRepository.findAll(new Specification<HCP>() {
#Override
public Predicate toPredicate(Root<HCP> root, CriteriaQuery<?> query, CriteriaBuilder criteriaBuilder) {
query.select(root.get("name")).distinct(true);
return criteriaBuilder.equal(root.get("area"), "Dhaka");
}
});
But it's not working. It's only applying district on the field that has #Id annotation. I want to apply distinct on area field.
Generated Hibernate Query looks like this:
select
distinct hcp0_.id as id1_0_,
hcp0_.area as area2_0_,
hcp0_.name as name3_0_
from
hcp hcp0_
where
hcp0_.area=?
How can I get generated query like the following?
select
distinct hcp0_.name as name3_0_
from
hcp hcp0_
where
hcp0_.area= 'Dhaka'
The desired result will list distinct names based on area.
How can I apply distinct on a specific field using JPA Specification?
Desired query and output:
You can't use Specifications because you want to return a List of Strings.
So you could use JPQL
#Query("select distinct h.name from Hcp h where area = 'Dhaka'")
List<String> findDistinctName();
I have two entities Questions and UserAnswers. I need to make an api in spring boot which returns all the columns from both the entities based on some conditions.
Conditions are:
I will be give a comparator eg: >, <, =, >=, <=
A column name eg: last_answered_at, last_seen_at
A value of the above column eg: 28-09-2020 06:00:18
I will need to return an inner join of the two entities and filter based on the above conditions.
Sample sql query based on above conditions will be like:
SELECT q,ua from questions q INNER JOIN
user_answers ua on q.id = ua.question_id
WHERE ua.last_answered_at > 28-09-2020 06:00:18
The problem I am facing is that the column name and the comparator for the query needs to be dynamic.
Is there an efficient way to do this using spring boot and JPA as I do not want to make jpa query methods for all possible combinations of columns and operators as it can be a very large number and there will be extensive use of if else?
I have developed a library called spring-dynamic-jpa to make it easier to implement dynamic queries with JPA.
You can use it to write the query templates. The query template will be built into different query strings before execution depending on your parameters when you invoke the method.
This sounds like a clear custom implementation of a repository method. Firstly, I will make some assumptions about the implementation of your entities. Afterwards, I will present an idea on how to solve your challenge.
I assume that the entities look basically like this (getters, setters, equals, hachCode... ignored).
#Entity
#Table(name = "questions")
public class Question {
#Id
#GeneratedValue
private Long id;
private LocalDateTime lastAnsweredAt;
private LocalDateTime lastSeenAt;
// other attributes you mentioned...
#OneToMany(mappedBy = "question", cascade = CascadeType.ALL, orphanRemoval = true)
private List<UserAnswer> userAnswers = new ArrayList();
// Add and remove methods added to keep bidirectional relationship synchronised
public void addUserAnswer(UserAnswer userAnswer) {
userAnswers.add(userAnswer);
userAnswer.setQuestion(this);
}
public void removeUserAnswer(UserAnswer userAnswer) {
userAnswers.remove(userAnswer);
userAnswer.setQuestion(null);
}
}
#Entity
#Table(name = "user_answers")
public class UserAnswer {
#Id
#GeneratedValue
private Long id;
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "task_release_id")
private Question question;
}
I will write the code with the knowledge about the JPA of Hibernate. For other JPAs, it might work similarly or the same.
Hibernate often needs the name of attributes as a String. To circumvent the issue of undetected mistakes (especially when refactoring), I suggest the module hibernate-jpamodelgen (see the class names suffixed with an underscore). You can also use it to pass the names of the attributes as arguments to your repository method.
Repository methods try to communicate with the database. In JPA, there are different ways of implementing database requests: JPQL as a query language and the Criteria API (easier to refactor, less error prone). As I am a fan of the Criteria API, I will use the Criteria API together with the modelgen to tell the ORM Hibernate to talk to the database to retrieve the relevant objects.
public class QuestionRepositoryCustomImpl implements QuestionRepository {
#PersistenceContext
private EntityManager entityManager;
#Override
public List<Question> dynamicFind(String comparator, String attribute, String value) {
CriteriaBuilder cb = entityManager.getCriteriaBuilder();
CriteriaQuery<Question> cq = cb.createQuery(Question.class);
// Root gets constructed for first, main class in the request (see return of method)
Root<Question> root = cq.from(Question.class);
// Join happens based on respective attribute within root
root.join(Question_.USER_ANSWER);
// The following ifs are not the nicest solution.
// The ifs check what comparator String contains and adds respective where clause to query
// This .where() is like WHERE in SQL
if("==".equals(comparator)) {
cq.where(cb.equal(root.get(attribute), value));
}
if(">".equals(comparator)) {
cq.where(cb.gt(root.get(attribute), value));
}
if(">=".equals(comparator)) {
cq.where(cb.ge(root.get(attribute), value));
}
if("<".equals(comparator)) {
cq.where(cb.lt(root.get(attribute), value));
}
if("<=".equals(comparator)) {
cq.where(cb.le(root.get(attribute), value));
}
// Finally, query gets created and result collected and returned as List
// Hint for READ_ONLY is added as lists are often just for read and performance is better.
return entityManager.createQuery(cq).setHint(QueryHints.READ_ONLY, true).getResultList();
}
}
I have a database table which holds Metadata for documents. My task now is to get a list with documenttypes. The documenttypes are not unique in the database table but of course I want them to be in my list. The sql is very simple:
SELECT DISTINCT groupname, group_displayorder
FROM t_doc_metadata
ORDER BY group_displayorder;
I have learned that I can use projections to get a subset of fields from my entity DocMetadata. I solved this as follows. My Entity:
#Entity
#Table(name="T_DOC_METADATA")
#Data
public class DocMetadata {
..............
#Column(nullable=false)
private String displayname;
#Column(nullable=false)
private Integer displayorder;
#Column(nullable=false)
private String groupname;
#Column(name="GROUP_DISPLAYORDER",
nullable=false)
private Integer groupDisplayorder;
#Column(name="METADATA_CHANGED_TS",
nullable=false,
columnDefinition="char")
private String metadataChangedTimestamp;
..........
}
My inteface for projection:
public interface GroupnameAndOrder {
String getGroupname();
Integer getGroupDisplayorder();
void setGroupname(String name);
void setGroupDisplayorder(int order);
}
Now I thought I'd be extraordinary clever by adding these lines to my repository:
#Query("select distinct d.groupname, d.groupDisplayorder from DocMetadata d order by d.groupDisplayorder")
public List<GroupnameAndOrder> findSortedGroupnames();
Sadly, when iterating over the result list and calling getGroupname() the result is null.
So I changed the lines in my repository according to the documentation:
public List<GroupnameAndOrder> findBy();
Now I get the groupnames but of course they are not unique now. So it doesn't solve my problem.
Is there any way to receive a ordered list with unique groupnames?
You are trying to be too clever. Instead just write the proper find method and return the GroupnameAndOrder. Spring Data JPA will then only retrieve what is needed for the projection.
Something like this should do the trick.
List<GroupnameAndOrder> findDistinctByOrderByGroupDisplayorder();
I am trying to utilize a NamedEntityGraph to limit the return data for specific queries. Mainly I do not want to return full object details when listing the object. A very simple class example is below.
#Entity
#Table(name="playerreport",schema="dbo")
#NamedEntityGraphs({
#NamedEntityGraph(name = "report.simple",
attributeNodes =
{#NamedAttributeNode(value="intId")
}
)
})
public class PlayerReportEntity {
#Id
#Column(name="intid",columnDefinition="uniqueidentifier")
private String intId;
#Column(name="plyid",columnDefinition="uniqueidentifier")
#Basic(fetch=FetchType.LAZY)
private String plyId;
#ManyToOne(fetch=FetchType.LAZY)
#JoinColumn(name = "plyid", insertable=false,updatable=false)
private PlayerEntity player;
No matter what I do to plyId and player are always returned. Is there any way to only return the requested columns (intId) ?
As for the collection Hibernate does not do the join for the player object but it still returns player as null. So that part is working to an extent.
I am using a JPARepository below to generate Crud Statements for me
public interface PlayerReportRepository extends JpaRepository<PlayerReportEntity, String> {
#EntityGraph(value="report.simple")
List<PlayerIntelEntity> findByPlyId(#Param(value = "playerId") String playerId);
#Override
#EntityGraph(value="report.simple")
public PlayerIntelEntity findOne(String id);
}
A chunk of text from here - "Hence it seems that the #NamedEntityGraph only affects fields that are Collections, but fields that are not a Collection are always loaded." from JIRA
Please use the Example 47 on this page and use repositories accordingly.
In essence, hibernate is right now loading all the feilds in the class and for collections it will work if you follow the example stated above.
Thanks.
I am using spring-data-jpa version 1.5.1.RELEASE .
My domain is :
public class MyDomain{
....
....
private String prop1;
private String prop2;
......
......
}
My JPA Specification is:
public final class MyDomainSpecs {
public static Specification<MyDomain> search(final String prop1,final String prop2) {
return new Specification<MyDomain>() {
public Predicate toPredicate(Root<MyDomain> root, CriteriaQuery<?> query, CriteriaBuilder cb) {
// Some tests if prop1 exist .....
Predicate predicate1 = cb.equal(root.get("prop1"), prop1);
Predicate predicate2 = cb.equal(root.get("prop2"), prop2);
return cb.and(predicate1, predicate2);
}
};
}
}
My Repository :
public interface MyDomainRepository extends JpaRepository<MyDomain, Long>, JpaSpecificationExecutor<MyDomain> {
List<MyDomain> findAll(Specification<MyDomain> spec);
}
All is Working .
But my need (For performance DB tunning) is to not return and select all fields of MyDomain from DB .
I need to select only for example tree properties (prop1, prop2, prop3) , idealy in a DTO Object .
I don't want to convert My List<MyDomain> to List<MyDto> because i am tunning DB request .
So , I don't find any way to do that with spring-data-Jpa and Specification .
Any Idea ?
Thanks
This is not possible as for now. There is a ticket for this but no idea if it will be ever implmented: https://jira.spring.io/browse/DATAJPA-51
Create a special version of MyDomain (e.g. MyDomainSummary or LightMyDomain) that only includes the fields you want to map.
Basic example
Borrowed from the excellent JPA WikiBook.
Assume a JPA entity (i.e. domain class) like so:
#Entity
#Table(name="EMPLOYEE")
public class BasicEmployee {
#Column(name="ID")
private long id;
#Column(name="F_NAME")
private String firstName;
#Column(name="L_NAME")
private String lastName;
// Any un-mapped field will be automatically mapped as basic and column name defaulted.
private BigDecimal salary;
}
The SQL query generated will be similar to
SELECT ID, F_NAME, L_NAME, SALARY FROM EMPLOYEE
if no conditions (where clause) are defined. So, to generalize the basic case one can say that the number of queried columns is equal to the number of mapped fields in your entity. Therefore, the fewer fields your entity, the fewer columns included in the SQL query.
You can have an Employee entity with e.g. 20 fields and a BasicEmployee as above with only 4 fields. Then you create different repositories or different repository methods for both.
Performance considerations
However, I seriously doubt you'll see noticeable performance improvements unless the fields you want to omit represent relationships to other entities. Before you start tweaking here log the SQL that is currently issued against the data base, then remove the columns you want to omit from that SQL, run it again and analyze what you gained.