I have an HQL as select p,c from Person p,ContactCard c where c.fk_pid=p.id I executed this query as HQL using this code:
List<Person> personsWithContactCard = new ArrayList<Person>();
List<object[]> quryResult = new ArrayList<object[]>();
String qry = "select p,c from Person p,ContactCard c where c.fk_pid=p.id";
quryResult = session.createQuery(qry).list();
for(object[] obj : quryResult )
{
Person person = new Person();
person = (Person)obj[0];
person.setContactCard = (ContactCard )obj[1];
personsWithContactCard.add(person);
person=null;
}
By taking query result in list of object array and looping on query result I fill persons list.
But after reading about ResultTransformer Interface I come to know that with this interface I can transform queryResult in to desired list so I changed my code To :
String qry = "select p,c from Person p,ContactCard c where c.fk_pid=p.id";
personsWithContactCard = session.createQuery(qry).setResultTransformer(new ResultTransformer() {
#Override
public Object transformTuple(Object[] tuple, String[] aliases)
{
Person person = new Person();
person = (Person)obj[0];
person.setContactCard = (ContactCard )obj[1];
return person ;
}
#Override
public List transformList(List collection)
{
return collection;
}
}).list();
This code gives me persons list with for looping.
So my question is : What is the difference between transformTuple and For loop?
Does the both are same in performance and processing sense?
Which will be more good as per performance?
And what is the use of transformList()?
Update :
After understanding use of ResultTransformer as explained in answer given by #bellabax I did one small change in code as follows:
personsWithContactCard = session.createQuery(qry).setResultTransformer(new ResultTransformer() {
#Override
public Object transformTuple(Object[] tuple, String[] aliases)
{
Person person = new Person();
person = (Person)obj[0];
person.setContactCard = (ContactCard )obj[1];
return person ;
}
#Override
public List transformList(List collection)
{
return null;
}
}).list();
I changed transformList() method to return null if I execute this code I am getting null personsWithContactCard list. Why transformList() method is need to return collection when I am not using it? And when I supposed to use transformList() and transformTuple() means how I can decide which to use?
There aren't differences in terms of result usually, but using a ResultTransformer:
is the standard Hibernate method to process tuple and future (break) changes about how HQL is processed and tuple returned will be masked by a ResultTransformer without code changes
give you the possibilities to decorate or delegate (for example)
so the choice is the ResultTransformer.
About ResultTransformer.transformList():
Here we have an opportunity to perform transformation on the query
result as a whole
instead in transformTuple you can manipulate only one row of returned set.
EDIT:
As quoted above the javadoc of ResultTransformer.transformList() is pretty clear: this function allow to modify the whole list to remove duplicate, apply type conversion and so on and the result of ResultTransformer.transformList() is forwarded to Query.list() method so, return null from transformList whill return null from list().
This is how Query and ResultTransformer are tied.
Related
I use JPA 1.0:
Query query;
query = em.createNamedQuery("getThresholdParameters");
query.setParameter(1, Integer.parseInt(circleId));
List<Object[]> resultList = new ArrayList();
resultList = query.getResultList();
Here I get result as List<Object[]>, thus I have to type convert all the parameters of the row to their respective types which is cumbersome.
In JPA 2.0 there is TypedQuery which return an entity object of type one specifies.
But as I am using JPA 1 I can't use it.
How to get result as Entity object of type I want??
EDIT:
QUERY
#Entity
#Table(name="GMA_THRESHOLD_PARAMETERS")
#NamedQuery(
name = "getThresholdParameters",
query = "select gmaTh.minNumberOc, gmaTh.minDurationOc, gmaTh.maxNumberIc, gmaTh.maxDurationIc, gmaTh.maxNumberCellId,"
+ "gmaTh.distinctBnumberRatio, gmaTh.minPercentDistinctBnumber from GmaThresholdParameter gmaTh "
+ "where gmaTh.id.circleId=?1 AND gmaTh.id.tspId=?2 AND gmaTh.id.flag=?3 "
)
Your query selects many fields. Such a query always returns a list of Object arrays. If you want a list containing instances of your GmaThresholdParameter entity, then the query should be
select gmaTh from GmaThresholdParameter gmaTh
where gmaTh.id.circleId=?1 AND gmaTh.id.tspId=?2 AND gmaTh.id.flag=?3
The code to get the list of entities would then be
List<GmaThresholdParameter> resultList = query.getResultList();
You'll get a type safety warning from the compiler, that you can ignore.
I can't respond to this as a comment so I'll just go ahead and make it an answer.
List<Object[]> resultList = new ArrayList(); // CREATE an empty ArrayList object
resultList = query.getResultList(); // getResultList ALSO returns its own ArrayList object
And since you assign the list that getResultList() returns to the same variable as you used for your own empty ArrayList, your application loses any connection to your own empty ArrayList and Java will collect it as garbage. Essentially you created it for absolutely no purpose.
what JB Nizet posted is enough.
List<GmaThresholdParameter> resultList = query.getResultList();
I have done something similar since I was using JPA 1 at that time:
final Collection<YourType> typedResult = new ArrayList<YourType>
for(final Object result : query.getResultList())
{
typedResult.add((YourType) result);
}
return typedResult;
List<GmaThresholdParamerter> result= query.getResultList();
for( GmaThresholdParamerter res : result)
{
System.out.println("" +res.getMinNumberOc());
System.out.println("" +res.getMinDurationOc());
}
I have some very complicated SQL (does some aggregation, some counts based on max value etc) so I want to use SQLQuery rather than Query. I created a very simple Pojo:
public class SqlCount {
private String name;
private Double count;
// getters, setters, constructors etc
Then when I run my SQLQuery, I want hibernate to populate a List for me, so I do this:
Query hQuery = sqlQuery.setResultTransformer(Transformers.aliasToBean(SqlCount.class));
Now I had a problem where depending on what the values are for 'count', Hibernate will variably retrieve it as a Long, Double, BigDecimal or BigInteger. So I use the addScalar function:
sqlQuery.addScalar("count", StandardBasicTypes.DOUBLE);
Now my problem. It seems that if you don't use the addScalar function, Hibernate will populate all of your fields with all of your columns in your SQL result (ie it will try to populate both 'name' and 'count'). However if you use the addScalar function, it only maps the columns that you listed, and all other columns seem to be discarded and the fields are left as null. In this instance, it wouldn't be too bad to just list both "name" and "count", but I have some other scenarios where I need a dozen or so fields - do I really have to list them all?? Is there some way in hibernate to say "map all fields automatically, like you used to, but by the way map this field as a Double"?
Is there some way in hibernate to say "map all fields automatically.
No, check the document here, find 16.1.1. Scalar queries section
The most basic SQL query is to get a list of scalars (values).
sess.createSQLQuery("SELECT * FROM CATS").list();
sess.createSQLQuery("SELECT ID, NAME, BIRTHDATE FROM CATS").list();
These will return a List of Object arrays (Object[]) with scalar values for each column in the CATS table. Hibernate will use ResultSetMetadata to deduce the actual order and types of the returned scalar values.
To avoid the overhead of using ResultSetMetadata, or simply to be more explicit in what is returned, one can use addScalar():
sess.createSQLQuery("SELECT * FROM CATS")
.addScalar("ID", Hibernate.LONG)
.addScalar("NAME", Hibernate.STRING)
.addScalar("BIRTHDATE", Hibernate.DATE)
i use this solution, I hope it will work with you.
with this solution you can populate what you select from the SQL, and return it as Map, and cast the values directly.
since hibernate 5.2 the method setResultTransformer() is deprecated but its work fine to me and works perfect.
if you hate to write extra code addScalar() for each column from the SQL, you can implement ResultTransformer interface and do the casting as you wish.
ex:
lets say we have this Query:
/*ORACLE SQL*/
SELECT
SEQ AS "code",
CARD_SERIAL AS "cardSerial",
INV_DATE AS "date",
PK.GET_SUM_INV(SEQ) AS "sumSfterDisc"
FROM INVOICE
ORDER BY "code";
note: i use double cote for case-sensitive column alias, check This
after create hibernate session you can create the Query like this:
/*Java*/
List<Map<String, Object>> list = session.createNativeQuery("SELECT\n" +
" SEQ AS \"code\",\n" +
" CARD_SERIAL AS \"cardSerial\",\n" +
" INV_DATE AS \"date\",\n" +
" PK.GET_SUM_INV(SEQ) AS \"sumSfterDisc\"\n" +
"FROM INVOICE\n" +
"ORDER BY \"code\"")
.setResultTransformer(new Trans())
.list();
now the point with Trans Class:
/*Java*/
public class Trans implements ResultTransformer {
private SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss", Locale.US);
#Override
public Object transformTuple(Object[] objects, String[] strings) {
Map<String, Object> map = new LinkedHashMap<>();
for (int i = 0; i < strings.length; i++) {
if (objects[i] == null) {
continue;
}
if (objects[i] instanceof BigDecimal) {
map.put(strings[i], ((BigDecimal) objects[i]).longValue());
} else if (objects[i] instanceof Timestamp) {
map.put(strings[i], dateFormat.format(((Timestamp) objects[i])));
} else {
map.put(strings[i], objects[i]);
}
}
return map;
}
#Override
public List transformList(List list) {
return list;
}
}
here you should override the two method transformTuple and transformList, in transformTuple you have two parameters the Object[] objects its the columns values of the row and String[] strings the names of the columns the hibernate Guaranteed the same order of of the columns as you order it in the query.
now the fun begin, for each row returned from the query the method transformTuple will be invoke, so you can build the row as Map or create new object with fields.
The objective is to get certain entities with specific ids. I want to create a vararg method that will take entity ids and return the entity list according to the ids:
#Override
public List<Entity> getEntities(long... ids) {
Session s = sessionFactory.getCurrentSession();
s.beginTransaction();
Criteria criteria = s.createCriteria(Entity.class);
for (long id : ids) {
// for very id I want to create a Restriction
// but Restriction goes like
// criteria.add(Restrictions.or(Restrictions.eq("id", id),Restrictions.eq("id", id)));
}
s.getTransaction().commit();
return null;
}
Usage will be:
List<Entity> list = getEntities(453,282,781,784);
How to create such criteria query?
A variable number of OR id = ? clause is like an IN clause. This is done using the Restrictions.in method:
criteria.add(Restrictions.in("id", ids));
criteria.add(Restrictions.in("id", ids));
criteria.addOrder(Order.asc("id"));
will solve your problem it will return your result in the same order which you passed into varargs
I'm trying to do something like:
List<Report> results = new ArrayList<Report>();
results = em.createQuery("SELECT u.firstname, u.lastname, u.workEmail FROM Employee u", Report.class)
.getResultList();
However, Report has more attributes than the 3 columns selected from the database(and does not have a specific constructor for those exact 3 attributes), so results is turned into a Vector of Object instead of an ArrayList of Report.
Is there a way to keep the results as an ArrayList and make all the other attributes of Report null ?
List data =em.createQuery("SELECT u.firstname, u.lastname, u.workEmail FROM Employee u", Report.class)
.getResultList();
List<Report> results = new ArrayList<Report>();
for (Object object : data) {
Map row = (Map) object;
Report report = new Report();
report.setFirstName(row.get("0"));
report.setLastName(row.get("1"));
report.setWorkEmail (row.get("2"));
results.add(report);
}
Two options, although I am not sure if the short one will work
Long option:
First subclass Report, add to the new class a constructor with the fields you want
public class MyReport extends Report {
public MyReport(String firstname, String lastname, String workEmail) {
...
}
}
And use the SELECT NEW construct
SELECT new MyReport(u.firstname, u.lastname, u.workEmail) FROM Employee u
Short option:
Exactly the same, but instead of creating a subclass, just implement the constructor in Report. I do not remember anything that would forbid this, but anyway I would test it carefully.
To answer the question directly: no. Of course you will get a RuntimeException if you try to execute your query as described above. The only solutions are:
Solution 1 As #Prabhakaran wrote and you noticed, use the selected strings in order to create a new Report like this:
List data =em.createQuery("SELECT u.firstname, u.lastname, u.workEmail FROM Employee u", Report.class).getResultList();
List<Report> results = new ArrayList<Report>();
for (Object object : data) {
Map row = (Map) object;
Report report = new Report();
String firstName = row.get("0");
String lastName = row.get("1");
String lastEmail = row.get("2");
results.add(new Report(firstName, null,..., lastName, ..., lastEmail));
}
Solution 2
As #SJuan76 said: use SELECT NEW and make a new constructor in Report with only three fields.
I do a query that returns a list of entities. How can I retrieve the entities from a ScrollableResults:
Session s = ....;
Query q = s.createQuery("....") # returns 100000s rows
ScrollableResults sr = q.scroll();
sr.scroll(45999); # just a number
Employee employee = ???
How do I get an employee in the last line of code
try the get(0) method, or get()[0]
Here's a link to API: ScrollableResults
get() returns the entire current row, get(index) returns object at index position without initializing the rest of them. There are also a bunch of convenience getXXX() methods that cast result to given type.
I do a query that returns a list of entities. How can I retrieve the entities from a ScrollableResults... How do I get an employee.
Just to improve the other answers, the ScrollableResults does the entity conversion for you although this isn't immediately clear from the Javadocs.
As #Bozho says, calling sr.get() will return the entity at the current location, but wrapped in an array. In looking at the code for ScrollableResultsImpl the current row's result is set with:
if ( result != null && result.getClass().isArray() ) {
currentRow = (Object[]) result;
} else {
currentRow = new Object[] { result };
}
So ScrollableResults.get() always returns an array of results and if your entity is not an array, it will be at get()[0].
So, with your code you would do something like:
while (sr.next()) {
// get the entity which is the first element in an Object[]
Employee employee = sr.get()[0];
...
}
To retrieve entities the simplest way would be to cast the object to whichever object you want:
E.g:
ScrollableResults sr = q.scroll();
while (sr.next()) {
CustomObject object = (CustomObject) sr.get()[0]; // Now CustomObject will have all the properties mapped
}
This works perfect for all the scenarios.