I have two tables (user, vehicles) and i want to write criteria query to retrieve data from db using criteria query specification and predicate to both Join Tables.
select ur.id, count (ur.vehicle_FK) from user so
inner join VEHICLE vhe on vhe.user_id_FK = ur."ID"
group by ur.id, vhe.user_id_FK;
How to implement it using criteria query ??
Try something like this :
Criteria criteria = session.createCriteria(User.class, "user");
criteria.createAlias("user.vehicle_FK", "vehicle", Criteria.INNER_JOIN);
criteria.setProjection(
Projections.projectionList().add(Projections.groupProperty("user.id"))
.add(Projections.countDistinct("user.id")));
Parameters in Criteria Queries
The following query string represents a JPQL query with a parameter:
SELECT c FROM Country c WHERE c.population > :p
An equivalent query can be built using the JPA criteria API as follows:
CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<Country> q = cb.createQuery(Country.class);
Root<Country> c = q.from(Country.class);
ParameterExpression<Integer> p = cb.parameter(Integer.class);
q.select(c).where(cb.gt(c.get("population"), p));
The ParameterExpression instance, p, is created to represent the query parameter. The where method sets the WHERE clause. As shown above, The CriteriaQuery interface supports method chaining. See the links in the next sections of this page for detailed explanations on how to set criteria query clauses and build criteria expressions.
You can find more examples here
https://www.objectdb.com/java/jpa/query/criteria
Remember to post an answer when you find one! :)
Related
Hi I use spring jpa to access my data in my spring boot project.I am wondering that is there any difference between #Query annatotation and critearia api in jpa.Are they totaly same or is there any difference(Their writing styles are different ,and I mean any performance or other issue between them)
Mostly I prefer #Query annotation it looks simple.Or any other option some one can advice like #Query or criteria api in spring jpa.And is there any disadvantages of #Query style?
#Query("SELECT u FROM User u WHERE u.status = 1")
Collection<User> findAllActiveUsers();
List<Book> findBooksByAuthorNameAndTitle(String authorName, String title) {
CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<Book> cq = cb.createQuery(Book.class);
Using #Query we can pass static query or pre compiled query so we can perform both select and non-select operations on the data
where as Criteria is suitable for executing Dynamic Queries such requirements occurs when data are know at run time
but using criteria api we can only perform select operations on the data.
For example
#Query(value = "SELECT u FROM User u")
List<User> findAllUsers(Sort sort);
We can also work with pre compiled query using #Query
For Example
#Query("SELECT u FROM User u WHERE u.status = :status and u.name = :name")
User findUserByStatusAndNameNamedParams(
#Param("status") Integer status,
#Param("name") String name);)
Dynamic queries like
Criteria cr = session.createCriteria(Employee.class);
// To get records having salary more than 2000
cr.add(Restrictions.gt("salary", 2000));
// To get records having salary less than 2000
cr.add(Restrictions.lt("salary", 2000));
Actual use of Dynamic queries comes when we'll encounter the need for building SQL statements based on conditions or data sets whose values are only known at runtime. And, in those cases, we can't just use a static query So we can't just use the #Query annotation since we can't provide a static SQL statement.In such case we use Criteria API
For more info follow the link provided
#Query and Criteria
I have a requirement to create a REST api. Api allows user to provide dynamic search criteria in URL. For example, let say I have NOTES table with column as Note_ID, NOTE_TEXT, STATUS, PERSON_ID. This table is used to keep notes of every person.
Now I want my REST api to be as https://server:host/MyApi/Notes?search=NoteText=='My Java adventure'. API should provide all notes having NOTE_TEXT as 'My Java adventure'. Similarly user can provide status also in url and also he can use operators as LIKE. I was able to do it via rsql parser as mentioned in https://www.baeldung.com/rest-api-search-language-rsql-fiql
Now I have additional requirement that based on user security person_id filter should be applied on query automatically.
I found that we can't have findBy method which can take Specification, Pageable and extra personId. For example I can't have a repository function as
findByPersonId(Specification spec, Pageable page, Long personId);
I thought of using SpEL to use it, but then I found that if we use #Query annotation on findBy method, Specifications are ignored.
Seems like there is no way I can have Specification and #Query both. I need to add more clauses using specification only. In reality my where clause is very complex which I have to append and getting it with Specification seems to be difficult. Its something like
Select * from NOTES where exists (select 'x' from ABC a where n.person_id = a.person_id)
Is there a way I can write #Query and also have Specification working on top of it?
Ideally I have achieve a query like
select * from test.SCH_FORUM_THREAD t
where exists (select 'x' from test.FORUM_THREAD_ACCESS fta, school.SCH_GROUP_PERSON gp
where gp.GROUP_ID = fta.GROUP_ID
and t.THREAD_ID = fta.THREAD_ID
and gp.PERSON_ID = :personId)
or exists (select 'x' from test.FORUM_THREAD_ACCESS fta
where fta.THREAD_ID = t.THREAD_ID
and fta.PERSON_ID = :personId);
So there are two exists clauses with or condition. I was able to make second exists by following How to write query(include subquery and exists) using JPA Criteria Builder
Now struggling with first exists as it has join also. Any idea how to do that with Specification.
Also as there are two exists, does that mean I need two specifications. Can I achieve it in one specification.
I was able to resolve it by creating a complex specification code. Something like
#Override
public Predicate toPredicate(Root<ForumThread> root, CriteriaQuery<?> query, CriteriaBuilder builder) {
Subquery<ForumThread> subQuery = query.subquery(ForumThread.class);
Root<ForumThread> subRoot = subQuery.from(ForumThread.class);
Join<ForumThreadAccess, GroupPerson> fragpjoin = subRoot.join("groupPersons");
Predicate threadPredicate = builder.equal(root.get("threadId"), subRoot.get("threadId"));
Predicate personPredicate = builder.equal(fragpjoin.get("personId"), personId);
subQuery.select(subRoot).where(threadPredicate, personPredicate);
Predicate existsGroupPredicate = builder.exists(subQuery);
Subquery<ForumThreadAccess> subQuery1 = query.subquery(ForumThreadAccess.class);
Root<ForumThreadAccess> subRoot1 = subQuery1.from(ForumThreadAccess.class);
Predicate threadPredicate1 = builder.equal(root.get("threadId"), subRoot1.get("threadId"));
Predicate personPredicate1 = builder.equal(subRoot1.get("personId"), personId);
subQuery1.select(subRoot1).where(threadPredicate1, personPredicate1);
Predicate existsPersonPredicate = builder.exists(subQuery1);
return builder.or(existsGroupPredicate,existsPersonPredicate);
}
To make it work your entities should also have proper #OneToMany and #ManyToMany in place.
Thanks
I am trying to fetch the employee details whose empltype is clerk and whose joining date is the recent one.
For which the query looks like following in SQL Server 2008:
select
*
from
employee jj
inner join
(
select
max(join_date) as jdate,
empltype as emptype
from
employee
where
empltype='clerk'
group by empltype
) mm
on jj.join_date=mm.jdate and jj.empltype=mm.emptype;
I am using SpringData JPA as my persistence layer using QuerylDSL,Specification and Predicate to fetch the data.
I am trying to convert the above query either in QueryDSL or Specification, but unable to hook them properly.
Employee Entity :
int seqid;(sequence id)
String empltype:
Date joindate;
String role;
Predicate method in Specifcation Class :
Predicate toPredicate(Root<employee> root,CriteriaQuery <?> query,CriteriaBuilder cb)
{
Predicate pred=null;
// Returning the rows matching the joining date
pred=cb.equal(root<Emplyoee_>.get("joindate"));
//**//
}
What piece of code should be written in //**// to convert about SQL query to JPA predicate. any other Spring Data JPA impl like #Query,NamedQuery or QueryDSL which returns Page also works for me.
Thanks in advance
I wrote this in notepad and it hasn't been tested but I think you're looking for something like
QEmployee e1 = new QEmployee("e1");
QEmployee e2 = new QEmployee("e2");
PathBuilder<Object[]> eAlias = new PathBuilder<Object[]>(Object[].class, "eAlias");
JPASubQuery subQuery = JPASubQuery().from(e2)
.groupBy(e2.empltype)
.where(e2.empltype.eq('clerk'))
.list(e2.join_date.max().as("jdate"), e2.emptype)
jpaQuery.from(e1)
.innerJoin(subQuery, eAlias)
.on(e1.join_date.eq(eAlias.get("jdate")), e1.emptype.eq(eAlias.get("emptype")))
.list(qEmployee);
I am implementing an autocomplete functionality using Jquery, when I type the name, it fetches the record from the db, The records stored in db are mixture of capital & small letters. I have written a HQL Query which fetches me the records with case-sensitive, but I need to records irrespective of case. Here is the query,
List<OrganizationTB> resultList = null;
Query query = session.createQuery("from DataOrganization dataOrg where dataOrg.poolName
like '%"+ poolName +"%'");
resultList = query.list();
Ex : If I have pool names, HRMS Data set, Hrms Data, Hr data etc... if I type HR or hr I need to get all the 3 records, which I'm not able to.
Please help...
change your query to
"from DataOrganization dataOrg where lower(dataOrg.poolName)
like lower('%"+ poolName +"%')"
for more information have a look 14.3 doc
A good solution is:
List<OrganizationTB> resultList = null;
Query query = session.createQuery("from DataOrganization dataOrg where lower(dataOrg.poolName) like lower(:poolName)");
query.setParameter("poolName", '%'+poolName+'%', StringType.INSTANCE);
resultList = query.list();
So you protect your code from SQL injection
Linq allows to express inner joins by using the join keyword or by using
SelectMany() (i.e. a couple of from keywords) with a where keyword:
var personsToState = from person in persons
join state in statesOfUS
on person.State equals state.USPS
select new { person, State = state.Name };
foreach (var item in personsToState)
{
System.Diagnostics.Debug.WriteLine(item);
}
// The same query can be expressed with the query operator SelectMany(), which is
// expressed as two from clauses and a single where clause connecting the sequences.
var personsToState2 = from person in persons
from state in statesOfUS
where person.State == state.USPS
select new { person, State = state.Name };
foreach (var item in personsToState2)
{
System.Diagnostics.Debug.WriteLine(item);
}
My question: when is it purposeful to use the join-style and when to use the where-style,
has one style performance advantages over the other style?
For local queries Join is more efficient due to its keyed lookup as Athari mentioned, however for LINQ to SQL (L2S) you'll get more mileage out of SelectMany. In L2S a SelectMany ultimately uses some type of SQL join in the generated SQL depending on your query.
Take a look at questions 11 & 12 of the LINQ Quiz by Joseph/Ben Albahari, authors of C# 4.0 In a Nutshell. They show samples of different types of joins and they state:
With LINQ to SQL, SelectMany-based
joins are the most flexible, and can
perform both equi and non-equi joins.
Throw in DefaultIfEmpty, and you can
do left outer joins as well!
In addition, Matt Warren has a detailed blog post on this topic as it pertains to IQueryable / SQL here: LINQ: Building an IQueryable provider - Part VII.
Back to your question of which to use, you should use whichever query is more readable and allows you to easily express yourself and construct your end goal clearly. Performance shouldn't be an initial concern unless you are dealing with large collections and have profiled both approaches. In L2S you have to consider the flexibility SelectMany offers you depending on the way you need to pair up your data.
Join is more efficient, it uses Lookup class (a variation of Dictionary with multiple values for a single key) to find matching values.