What is the proper way to cast Hibernate Query list to List Type

Question

I m a newbie with Hibernate  and I m writing a simple method to return a list of objects matching a specific filter  List lt Foo gt  seemed a natural return type   Whatever I do  I can t seem to make the compiler happy  unless I employ an ugly  SuppressWarnings   import java util List  import org hibernate Query  import org hibernate Session   public class Foo        public Session acquireSession                All DB opening  connection etc  removed             since the problem is in compilation  not at runtime          return null              SuppressWarnings  unchecked       lt -----         public List lt Foo gt  activeObjects             Session s   acquireSession            Query   q   s createQuery  from foo where active            return  List lt Foo gt   q list              I would like to get rid of that SuppressWarnings  But if I do  I get the warning  Warning  Unchecked cast from List to List lt Foo gt     I can ignore it  but I d like to not get it in the first place   and if I remove the  generic to conform to  list   return type  I get the warning  Warning  List is a raw type  References to generic type List lt E gt  should be parameterized    I noticed that org hibernate mapping does declare a List  but it is a different type altogether - Query returns a java util List  as a raw type  I find it odd that a recent Hibernate  4 0 x  would not implement parameterized types  so I suspect that it s me instead doing something wrong   It looks very much like Cast Hibernate result to a list of objects  but here I have no  hard  errors  the system knows type Foo  and I m not using a SQLQuery but a straight Query   So no joy   I have also looked at Hibernate Class Cast Exception since it looked promising  but then I realized that I do not actually get any Exception    my problem is just that of a warning - a coding style  if you will   Documentation on jboss org  Hibernate manuals and several tutorials do not seem to cover the topic in such detail  or I didn t search in the right places    When they do enter into detail  they use on-the-fly casting - and this on tutorials that weren t on the official jboss org site  so I m a bit wary   The code  once compiled  runs with no apparent problem    that I know of    yet  and the results are the expected ones   So  am I doing this right  Am I missing something obvious  Is there an  official  or  recommended  Way To Do It

User · Accepted Answer

Short answer  SuppressWarnings is the right way to go   Long answer  Hibernate returns a  raw List from the Query list method  see here  This is not a bug with Hibernate or something the can be solved  the type returned by the query is not known at compile time   Therefore when you write  final List lt MyObject gt  list   query list      You are doing an unsafe cast from List to List lt MyObject gt  - this cannot be avoided   There is no way you can safely carry out the cast as the List could contain anything   The only way to make the error go away is the even more ugly  final List lt MyObject gt  list   new LinkedList lt  gt     for final Object o   query list          list add  MyObject o

User · Answer

The resolution is to use TypedQuery instead  When creating a query from the EntityManager instead call it like this    TypedQuery lt  YourClass  gt  query   entityManager createQuery   your sql     YourClass  class   List lt  YourClass  gt  list   query getResultList      no type warning   This also works the same for named queries  native named queries  etc  The corresponding methods have the same names as the ones that would return the vanilla query  Just use this instead of a Query whenever you know the return type

User · Answer

Only way that work for me was with an Iterator   Iterator iterator  query list   iterator    Destination dest  ArrayList lt Destination gt  destinations  new ArrayList lt  gt     Iterator iterator  query list   iterator        while iterator hasNext             Object   tuple   Object    iterator next            dest  new Destination            dest setId  String tuple 0            dest setName  String tuple 1            dest setLat  String tuple 2            dest setLng  String tuple 3            destinations add dest           With other methods that I found  I had cast problems

User · Answer

I found the best solution here  the key of this issue is the  addEntity method  public static void testSimpleSQL         final Session session   sessionFactory openSession        SQLQuery q   session createSQLQuery  select   from ENTITY        q addEntity Entity class       List lt Entity gt  entities   q list        for  Entity entity   entities            System out println entity

User · Answer

List lt Person gt  list   new ArrayList lt Person gt     Criteria criteria   this getSessionFactory   getCurrentSession   createCriteria Person class   for  final Object o   criteria list          list add  Person  o

User · Answer

You use a ResultTransformer like that   public List lt Foo gt  activeObjects         Session s   acquireSession        Query   q   s createQuery  from foo where active        q setResultTransformer Transformers aliasToBean Foo class        return  List lt Foo gt   q list

User · Answer

You can avoid compiler warning with workarounds like this one   List lt   gt  resultRaw   query list    List lt MyObj gt  result   new ArrayList lt MyObj gt  resultRaw size     for  Object o   resultRaw        result add  MyObj  o       But there are some issues with this code    created superfluous ArrayList unnecessary loop over all elements returned from the query longer code    And the difference is only cosmetic  so using such workarounds is - in my opinion - pointless   You have to live with these warnings or suppress them

User · Answer

Just just using Transformers It did not work for me I was getting type cast exception    sqlQuery setResultTransformer Transformers aliasToBean MYEngityName class   did notwork because I was getting Array of Object in the return list element not the fixed MYEngityName type of list element    It worked for me when I make following changes When I have added sqlQuery addScalar -  each selected column and its type and for specific String type column we dont have to map its type  like addScalar  langCode       And I have join MYEngityName with NextEnity we cant just select   in the Query  it will give array of Object in the return list    Below code sample     session   ht getSessionFactory   openSession                    String sql   new StringBuffer  Select txnId nft mId count retryReason langCode FROM  MYEngityName nft INNER JOIN NextEntity m on nft mId     m id where nft txnId  lt     append lastTxnId                          append StringUtils isNotBlank regionalCountryOfService     And  m countryOfService in      regionalCountryOfService                                    append   order by nft txnId desc   toString                    SQLQuery sqlQuery   session createSQLQuery sql                   sqlQuery setResultTransformer Transformers aliasToBean MYEngityName class                    sqlQuery addScalar  txnId  Hibernate LONG                           addScalar  merchantId  Hibernate INTEGER                           addScalar  count  Hibernate BYTE                           addScalar  retryReason                            addScalar  langCode                    sqlQuery setMaxResults maxLimit                   return sqlQuery list      It might help some one  in this way work for me

User · Answer

The proper way is to use Hibernate Transformers   public class StudentDTO   private String studentName  private String courseDescription   public StudentDTO                     List resultWithAliasedBean   s createSQLQuery   SELECT st name as studentName  co description as courseDescription      FROM Enrolment e      INNER JOIN Student st on e studentId st studentId      INNER JOIN Course co on e courseCode co courseCode    setResultTransformer  Transformers aliasToBean StudentDTO class    list     StudentDTO dto   StudentDTO  resultWithAliasedBean get 0     Iterating througth Object   is redundant and would have some performance penalty  Detailed information about transofrmers usage you will find here  Transformers for HQL and SQL  If you are looking for even more simple solution you can use out-of-the-box-map-transformer   List iter   s createQuery   select e student name as studentName             e course description as courseDescription     from   Enrolment as e    setResultTransformer  Transformers ALIAS TO ENTITY MAP    iterate     String name    Map  iter next    get  studentName

User · Answer

To answer your question  there is no  proper way  to do that  Now if it s just the warning that bothers you  the best way to avoid its proliferation is to wrap the Query list   method into a DAO    public class MyDAO         SuppressWarnings  unchecked       public static  lt T gt  List lt T gt  list Query q           return q list              This way you get to use the  SuppressWarnings  unchecked   only once

[java] What is the "proper" way to cast Hibernate Query.list() to List<Type>?

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