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Using Optional for getSingleResult

What is a raw type and why shouldn't we use it?Java optional parametersUses for OptionalWhat is an optional value in Swift?Why create “Implicitly Unwrapped Optionals”, since that implies you know there's a value?Should Java 8 getters return optional type?Why should Java 8's Optional not be used in argumentsWhat does “fatal error: unexpectedly found nil while unwrapping an Optional value” mean?JEE, eclipselink, glassfish4.0 can't persist entityWebService - could not initialize proxy - no SessionEnvers query - return REVTYPE along with modified fields

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0

Hello I have a question about Optional.
Optional should be used when there is possibility then null can be returned.
I wanted to use it to find the image by item id.
So in DAO:

 @Override
 public Optional findImage(int itemId) 
 Session currentSession = entityManager.unwrap(Session.class);
 return currentSession
 .createQuery("select from Image as i where it.itemId=:itemId")
 .setParameter("itemId", itemId)
 .setMaxResults(1)
 .getResultList()
 .stream()
 .findFirst();
 

In service:

@Override
public Image findImage(int itemId) 
 LOGGER.info("Getting image by item id: ", itemId);
 Optional opt = this.imageDAO.findImage(itemId);
 return opt.orElseThrow(() -> new ImageNotFound("The image for item with id: " + itemId + " was not found"));

But I can not get the value or throw the specific error.

Can anybody explain how I should approach the getting single result via Optional?

Thanks!!

java spring hibernate optional

share|improve this question

asked Mar 25 at 21:09

ErnestoErnesto

1771515 bronze badges

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  Check the syntax of the query , sounds like some thing is missing here. Try select i from Image as it where it.itemId=:itemId
  
  – Gopi
  Mar 25 at 21:12
  
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  "I can not get the value or throw the specific error". Clarify.
  
  – LppEdd
  Mar 25 at 21:13
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  You're the third one I see today unwrapping the EntityManager to use the Hibernate proprietary Session. Why are you doing that? What's the point, except making your code awkward and not portable? You can execute queries using the EntityManager directly. No need to unwrap.
  
  – JB Nizet
  Mar 25 at 21:15
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Are you asking what you can do with an Optional? The javadoc is your friend: docs.oracle.com/javase/8/docs/api/java/util/Optional.html. If not, then once again, clarify: what do you want to achieve, precisely?
  
  – JB Nizet
  Mar 25 at 21:28
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  Assuming you're using java.util.Optional, you are returning the raw type. This means all the methods that return the wrapped value return Object. You should declare the return type as Optional<Image>. If that's not your problem (or really even if it is) you should edit your question to add clarification. Describe what you're trying to do, what's actually happening, and include the exact error(s) you're getting. See minimal reproducible example and How to Ask.
  
  – Slaw
  Mar 25 at 21:42
  
  

  
  
  
  

 | 
show 4 more comments

0

Hello I have a question about Optional.
Optional should be used when there is possibility then null can be returned.
I wanted to use it to find the image by item id.
So in DAO:

 @Override
 public Optional findImage(int itemId) 
 Session currentSession = entityManager.unwrap(Session.class);
 return currentSession
 .createQuery("select from Image as i where it.itemId=:itemId")
 .setParameter("itemId", itemId)
 .setMaxResults(1)
 .getResultList()
 .stream()
 .findFirst();
 

In service:

@Override
public Image findImage(int itemId) 
 LOGGER.info("Getting image by item id: ", itemId);
 Optional opt = this.imageDAO.findImage(itemId);
 return opt.orElseThrow(() -> new ImageNotFound("The image for item with id: " + itemId + " was not found"));

But I can not get the value or throw the specific error.

Can anybody explain how I should approach the getting single result via Optional?

Thanks!!

java spring hibernate optional

share|improve this question

asked Mar 25 at 21:09

ErnestoErnesto

1771515 bronze badges

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  Check the syntax of the query , sounds like some thing is missing here. Try select i from Image as it where it.itemId=:itemId
  
  – Gopi
  Mar 25 at 21:12
  
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  "I can not get the value or throw the specific error". Clarify.
  
  – LppEdd
  Mar 25 at 21:13
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  You're the third one I see today unwrapping the EntityManager to use the Hibernate proprietary Session. Why are you doing that? What's the point, except making your code awkward and not portable? You can execute queries using the EntityManager directly. No need to unwrap.
  
  – JB Nizet
  Mar 25 at 21:15
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Are you asking what you can do with an Optional? The javadoc is your friend: docs.oracle.com/javase/8/docs/api/java/util/Optional.html. If not, then once again, clarify: what do you want to achieve, precisely?
  
  – JB Nizet
  Mar 25 at 21:28
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  Assuming you're using java.util.Optional, you are returning the raw type. This means all the methods that return the wrapped value return Object. You should declare the return type as Optional<Image>. If that's not your problem (or really even if it is) you should edit your question to add clarification. Describe what you're trying to do, what's actually happening, and include the exact error(s) you're getting. See minimal reproducible example and How to Ask.
  
  – Slaw
  Mar 25 at 21:42
  
  

  
  
  
  

 | 
show 4 more comments

Hello I have a question about Optional.
Optional should be used when there is possibility then null can be returned.
I wanted to use it to find the image by item id.
So in DAO:

 @Override
 public Optional findImage(int itemId) 
 Session currentSession = entityManager.unwrap(Session.class);
 return currentSession
 .createQuery("select from Image as i where it.itemId=:itemId")
 .setParameter("itemId", itemId)
 .setMaxResults(1)
 .getResultList()
 .stream()
 .findFirst();
 

In service:

@Override
public Image findImage(int itemId) 
 LOGGER.info("Getting image by item id: ", itemId);
 Optional opt = this.imageDAO.findImage(itemId);
 return opt.orElseThrow(() -> new ImageNotFound("The image for item with id: " + itemId + " was not found"));

But I can not get the value or throw the specific error.

Can anybody explain how I should approach the getting single result via Optional?

Thanks!!

java spring hibernate optional

share|improve this question

asked Mar 25 at 21:09

ErnestoErnesto

1771515 bronze badges

 @Override
 public Optional findImage(int itemId) 
 Session currentSession = entityManager.unwrap(Session.class);
 return currentSession
 .createQuery("select from Image as i where it.itemId=:itemId")
 .setParameter("itemId", itemId)
 .setMaxResults(1)
 .getResultList()
 .stream()
 .findFirst();
 

@Override
public Image findImage(int itemId) 
 LOGGER.info("Getting image by item id: ", itemId);
 Optional opt = this.imageDAO.findImage(itemId);
 return opt.orElseThrow(() -> new ImageNotFound("The image for item with id: " + itemId + " was not found"));

share|improve this question

asked Mar 25 at 21:09

ErnestoErnesto

1771515 bronze badges

share|improve this question

asked Mar 25 at 21:09

ErnestoErnesto

1771515 bronze badges

asked Mar 25 at 21:09

ErnestoErnesto

1771515 bronze badges

asked Mar 25 at 21:09

ErnestoErnesto

1771515 bronze badges

1 Answer
1

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oldest

votes

1

EDIT

As mentioned by @Slaw, my previous answer was incorrect and I have assumed that the code posted in the question has no compilation issue. Anyway, here's the updated answer based on the @Slaw's comment.

Basically the code wouldn't compile because it's unable to infer the type of Optional to return. So just parameterize Optional

@Override
public Image findImage(int itemId) 
 LOGGER.info("Getting image by item id: ", itemId);
 Optional<Image> opt = this.imageDAO.findImage(itemId); <== parameterize Optional
 return opt.orElseThrow(() -> new ImageNotFound("The image for item with id: " + itemId + " was not found"));

share|improve this answer

edited Mar 29 at 17:04

answered Mar 26 at 6:40

Tan Kim LoongTan Kim Loong

61155 silver badges1212 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  How is this correct? No matter what Optional the OP is using (java.util.Optional or some other), your solution assumes the wrapped value, returned by get, has an orElseThrow method. Why would it? And assuming we're using java.util.Optional, the orElseThrow method will return the value if present, otherwise it will throw the exception returned by the supplier. The get method will throw a NoSuchElementException if no value is present. And you're still using the raw type, so get and orElseThrow return Object, not Image, and this should still fail to compile.
  
  – Slaw
  Mar 27 at 15:57
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  You are absolutely correct. I was under the assumption that the code provided in the question would already compile. A mistake on my side. You should provide your answer instead, or I will edit mine to reflect your point. Should have verified my answer properly!
  
  – Tan Kim Loong
  Mar 28 at 3:13
  

  
  
  
  

add a comment | 

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1

EDIT

As mentioned by @Slaw, my previous answer was incorrect and I have assumed that the code posted in the question has no compilation issue. Anyway, here's the updated answer based on the @Slaw's comment.

Basically the code wouldn't compile because it's unable to infer the type of Optional to return. So just parameterize Optional

@Override
public Image findImage(int itemId) 
 LOGGER.info("Getting image by item id: ", itemId);
 Optional<Image> opt = this.imageDAO.findImage(itemId); <== parameterize Optional
 return opt.orElseThrow(() -> new ImageNotFound("The image for item with id: " + itemId + " was not found"));

share|improve this answer

edited Mar 29 at 17:04

answered Mar 26 at 6:40

Tan Kim LoongTan Kim Loong

61155 silver badges1212 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  How is this correct? No matter what Optional the OP is using (java.util.Optional or some other), your solution assumes the wrapped value, returned by get, has an orElseThrow method. Why would it? And assuming we're using java.util.Optional, the orElseThrow method will return the value if present, otherwise it will throw the exception returned by the supplier. The get method will throw a NoSuchElementException if no value is present. And you're still using the raw type, so get and orElseThrow return Object, not Image, and this should still fail to compile.
  
  – Slaw
  Mar 27 at 15:57
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  You are absolutely correct. I was under the assumption that the code provided in the question would already compile. A mistake on my side. You should provide your answer instead, or I will edit mine to reflect your point. Should have verified my answer properly!
  
  – Tan Kim Loong
  Mar 28 at 3:13
  

  
  
  
  

add a comment | 

1

EDIT

As mentioned by @Slaw, my previous answer was incorrect and I have assumed that the code posted in the question has no compilation issue. Anyway, here's the updated answer based on the @Slaw's comment.

Basically the code wouldn't compile because it's unable to infer the type of Optional to return. So just parameterize Optional

@Override
public Image findImage(int itemId) 
 LOGGER.info("Getting image by item id: ", itemId);
 Optional<Image> opt = this.imageDAO.findImage(itemId); <== parameterize Optional
 return opt.orElseThrow(() -> new ImageNotFound("The image for item with id: " + itemId + " was not found"));

share|improve this answer

edited Mar 29 at 17:04

answered Mar 26 at 6:40

Tan Kim LoongTan Kim Loong

61155 silver badges1212 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  How is this correct? No matter what Optional the OP is using (java.util.Optional or some other), your solution assumes the wrapped value, returned by get, has an orElseThrow method. Why would it? And assuming we're using java.util.Optional, the orElseThrow method will return the value if present, otherwise it will throw the exception returned by the supplier. The get method will throw a NoSuchElementException if no value is present. And you're still using the raw type, so get and orElseThrow return Object, not Image, and this should still fail to compile.
  
  – Slaw
  Mar 27 at 15:57
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  You are absolutely correct. I was under the assumption that the code provided in the question would already compile. A mistake on my side. You should provide your answer instead, or I will edit mine to reflect your point. Should have verified my answer properly!
  
  – Tan Kim Loong
  Mar 28 at 3:13
  

  
  
  
  

add a comment | 

EDIT

As mentioned by @Slaw, my previous answer was incorrect and I have assumed that the code posted in the question has no compilation issue. Anyway, here's the updated answer based on the @Slaw's comment.

Basically the code wouldn't compile because it's unable to infer the type of Optional to return. So just parameterize Optional

@Override
public Image findImage(int itemId) 
 LOGGER.info("Getting image by item id: ", itemId);
 Optional<Image> opt = this.imageDAO.findImage(itemId); <== parameterize Optional
 return opt.orElseThrow(() -> new ImageNotFound("The image for item with id: " + itemId + " was not found"));

share|improve this answer

edited Mar 29 at 17:04

answered Mar 26 at 6:40

Tan Kim LoongTan Kim Loong

61155 silver badges1212 bronze badges

@Override
public Image findImage(int itemId) 
 LOGGER.info("Getting image by item id: ", itemId);
 Optional<Image> opt = this.imageDAO.findImage(itemId); <== parameterize Optional
 return opt.orElseThrow(() -> new ImageNotFound("The image for item with id: " + itemId + " was not found"));

share|improve this answer

edited Mar 29 at 17:04

answered Mar 26 at 6:40

Tan Kim LoongTan Kim Loong

61155 silver badges1212 bronze badges

answered Mar 26 at 6:40

Tan Kim LoongTan Kim Loong

61155 silver badges1212 bronze badges

answered Mar 26 at 6:40

Tan Kim LoongTan Kim Loong

61155 silver badges1212 bronze badges