JPA getSingleResult or null

Question

I have an insertOrUpdate method which inserts an Entity when it doesn t exist or update it if it does  To enable this  I have to findByIdAndForeignKey  if it returned null insert if not then update  The problem is how do I check if it exists  So I tried getSingleResult  But it throws an exception if the  public Profile findByUserNameAndPropertyName String userName  String propertyName        String namedQuery   Profile class getSimpleName       findByUserNameAndPropertyName       Query query   entityManager createNamedQuery namedQuery       query setParameter  name   userName       query setParameter  propName   propertyName       Object result   query getSingleResult        if  result    null  return null      return  Profile  result      but getSingleResult throws an Exception    Thanks

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If you wish to use the try catch mechanism to handle this problem   then it can be used to act  like if else  I used the try catch to add a new record when I didn t find an existing one   try      if part      record   query getSingleResult             use the record from the fetched result    catch NoResultException e     else part       create a new record      record   new Record                        entityManager persist record

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I ve done  in Java 8    query getResultList   stream   findFirst   orElse null

User · Answer

Try this in Java 8   Optional first   query getResultList   stream   findFirst

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Here s a good option for doing this   public static  lt T gt  T getSingleResult TypedQuery lt T gt  query        query setMaxResults 1       List lt T gt  list   query getResultList        if  list    null    list isEmpty              return null             return list get 0

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From JPA 2 2  instead of  getResultList   and checking if list is empty or creating a stream you can return stream and take first element    getResultStream    findFirst    orElse null

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I encapsulated the logic in the following helper method   public class JpaResultHelper       public static Object getSingleResultOrNull Query query           List results   query getResultList            if  results isEmpty    return null          else if  results size      1  return results get 0           throw new NonUniqueResultException

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Here s another extension  this time in Scala   customerQuery getSingleOrNone match     case Some c    gt           case None      gt             With this pimp   import javax persistence  NonUniqueResultException  TypedQuery  import scala collection JavaConversions    object Implicits      class RichTypedQuery T  q  TypedQuery T          def getSingleOrNone   Option T             val results   q setMaxResults 2  getResultList        if  results isEmpty          None       else if  results size    1          Some results head        else         throw new NonUniqueResultException                implicit def query2RichQuery T  q  TypedQuery T     new RichTypedQuery T  q

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So don t do that   You have two options    Run a selection to obtain the COUNT of your result set  and only pull in the data if this count is non-zero  or Use the other kind of query  that gets a result set  and check if it has 0 or more results  It should have 1  so pull that out of your result collection and you re done    I d go with the second suggestion  in agreement with Cletus  It gives better performance than  potentially  2 queries  Also less work

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Here s a typed generics version  based on Rodrigo IronMan s implementation    public static  lt T gt  T getSingleResultOrNull TypedQuery lt T gt  query        query setMaxResults 1       List lt T gt  list   query getResultList        if  list isEmpty              return null            return list get 0

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Spring has a utility method for this   TypedQuery lt Profile gt  query   em createNamedQuery namedQuery  Profile class       return org springframework dao support DataAccessUtils singleResult query getResultList

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Thats works to me   Optional lt Object gt  opt   Optional ofNullable nativeQuery getSingleResult     return opt isPresent     opt get     null

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The undocumented method uniqueResultOptional in org hibernate query Query should do the trick  Instead of having to catch a NoResultException you can just call query uniqueResultOptional   orElse null

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I solved this by using List lt   gt  myList   query getResultList    and checking if myList size   equals to zero

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Throwing an exception is how getSingleResult   indicates it can t be found  Personally I can t stand this kind of API  It forces spurious exception handling for no real benefit  You just have to wrap the code in a try-catch block   Alternatively you can query for a list and see if its empty  That doesn t throw an exception  Actually since you re not doing a primary key lookup technically there could be multiple results  even if one  both or the combination of your foreign keys or constraints makes this impossible in practice  so this is probably the more appropriate solution

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There is an alternative which I would recommend    Query query   em createQuery  your query    List lt Element gt  elementList   query getResultList    return CollectionUtils isEmpty elementList     null   elementList get 0     This safeguards against Null Pointer Exception  guarantees only 1 result is returned

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Look this code    return query getResultList   stream   findFirst   orElse null    When findFirst   is called maybe can be throwed a NullPointerException   the best aproach is   return query getResultList   stream   filter Objects  nonNull  findFirst   orElse null

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I achieved this by  getting a result list then checking if it is empty  public boolean exist String value            List lt Object gt  options   getEntityManager   createNamedQuery  AppUsers findByEmail   setParameter  email   value  getResultList            return  options isEmpty            It is so annoying that getSingleResult   throws exceptions  Throws    NoResultException - if there is no result NonUniqueResultException - if more than one result and some other exception that you can get more info on from their documentation

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Combining the useful bits of the existing answers  limiting the number of results  checking that the result is unique  and using the estabilshed method name  Hibernate   we get          Return a single instance that matches the query  or null if the query returns no results         param query query  required      param  lt T gt  result record type     return record or null     public static  lt T gt  T uniqueResult  NotNull TypedQuery lt T gt  query        List lt T gt  results   query setMaxResults 2  getResultList        if  results size    gt  1  throw new NonUniqueResultException        return results isEmpty     null   results get 0

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So all of the  try to rewrite without an exception  solution in this page has a minor problem  Either its not throwing NonUnique exception  nor throw it in some wrong cases too  see below    I think the proper solution is  maybe  this   public static  lt L gt  L getSingleResultOrNull TypedQuery lt L gt  query        List lt L gt  results   query getResultList        L foundEntity   null      if  results isEmpty              foundEntity   results get 0             if results size    gt  1            for L result   results                if result    foundEntity                    throw new NonUniqueResultException                                      return foundEntity      Its returning with null if there is 0 element in the list  returning nonunique if there are different elements in the list  but not returning nonunique when one of your select is not properly designed and returns the same object more then one times   Feel free to comment

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Here s the same logic as others suggested  get the resultList  return its only element or null   using Google Guava and a TypedQuery   public static  lt T gt  getSingleResultOrNull final TypedQuery lt T gt  query        return Iterables getOnlyElement query getResultList    null        Note that Guava will return the unintuitive IllegalArgumentException if the result set has more than one result   The exception makes sense to clients of getOnlyElement    as it takes the result list as its argument  but is less understandable to clients of getSingleResultOrNull

[java] JPA getSingleResult() or null

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