use of entityManager createNativeQuery query foo class

Question

I would like to return a List of Integers from a   javax persistence EntityManager createNativeQuery call  Why is the following incorrect   entityManager createNativeQuery  Select P AppID From P   Integer class     specifically why do I get     Unknown entity  java lang Integer   Would I have to create an entity class that has a single field that is an Integer    Thanks

User · Accepted Answer

What you do is called a projection  That s when you return only a scalar value that belongs to one entity  You can do this with JPA  See scalar value   I think in this case  omitting the entity type altogether is possible      Query query   em createNativeQuery    select id from users where username             query setParameter 1   lt         BigDecimal val    BigDecimal  query getSingleResult       Example taken from here

User · Answer

That doesn t work because the second parameter should be a mapped entity and of course Integer is not a persistent class  since it doesn t have the  Entity annotation on it    for you you should do the following   Query q   em createNativeQuery  select id from users where username    username    q setParameter  username    lt    List lt BigDecimal gt  values   q getResultList      or if you want to use HQL you can do something like this   Query q   em createQuery  select new Integer id  from users where username    username    q setParameter  username    lt    List lt Integer gt  values   q getResultList      Regards

User · Answer

JPA was designed to provide an automatic mapping between Objects and a relational database  Since Integer is not a persistant entity  why do you need to use JPA   A simple JDBC request will work fine

User · Answer

Suppose your query is  select id name from users where rollNo   1001     Here query will return a object with id and name column  Your Response class is like bellow   public class UserObject          int id          String name          String rollNo           public UserObject Object   columns                this id    columns 0     null    BigDecimal columns 0   intValue   0              this name    String  columns 1                      public int getId                 return id                     public void setId int id                this id   id                     public String getName                 return name                     public void setName String name                this name   name                     public String getRollNo                 return rollNo                     public void setRollNo String rollNo                this rollNo   rollNo                    here UserObject constructor will get a Object Array and set data with object     public UserObject Object   columns                this id    columns 0     null    BigDecimal columns 0   intValue   0              this name    String  columns 1               Your query executing function is like bellow    public UserObject getUserByRoll EntityManager entityManager String rollNo             String queryStr    select id name from users where rollNo    1           try               Query query   entityManager createNativeQuery queryStr               query setParameter 1  rollNo                return new UserObject  Object    query getSingleResult               catch  Exception e                e printStackTrace                throw e                    Here you have to import bellow packages   import javax persistence Query  import javax persistence EntityManager    Now your main class  you have to call this function   First you have to get EntityManager and call this getUserByRoll EntityManager entityManager String rollNo  function  Calling procedure is given bellow    PersistenceContext private EntityManager entityManager   UserObject userObject   getUserByRoll entityManager  1001      Now you have data in this userObject   Here is Imports   import javax persistence EntityManager  import javax persistence PersistenceContext    Note   query getSingleResult   return a array  You have to maintain the column position and data type   select id name from users where rollNo    1    query return a array and it s  0  -- gt  id and  1  - gt  name   For more info  visit this Answer  Thanks

User · Answer

Here is a DB2 Stored Procidure that receive a parameter SQL CREATE PROCEDURE getStateByName  IN StateName VARCHAR 128   DYNAMIC RESULT SETS 1 P1  BEGIN     -- Declare cursor     DECLARE State Cursor CURSOR WITH RETURN for     --                                                                             --   Replace the SQL statement with your statement      --   Note  Be sure to end statements with the terminator character  usually          --       --   The example SQL statement SELECT NAME FROM SYSIBM SYSTABLES     --   returns all names from SYSIBM SYSTABLES      --                                                                            SELECT   FROM COUNTRY STATE     WHERE PROVINCE NAME LIKE UPPER stateName       -- Cursor left open for client application     OPEN Province Cursor  END P1  Java   Country is a db2 scheme    Now here is a java Entity bean Method  public List lt Province gt  getStateByName String stateName  throws Exception        EntityManager em   this em      List lt State gt  states  null      try           Query query   em createNativeQuery  quot call NGB getStateByName  1  quot   Province class           query setParameter 1  provinceName           states   List lt Province gt   query getResultList          catch  Exception ex            throw ex             return states

[java] use of entityManager.createNativeQuery(query,foo.class)

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