django - get returned more than one topic

Question

When I tried to relate an attribute with another one which has an M to M relation I received this error      get   returned more than one topic -- it returned 2    Can you guys tell me what that means and maybe tell me in advance how to avoid this error    models  class LearningObjective models Model       learning objective models TextField    class Topic models Model       learning objective topic models ManyToManyField LearningObjective      topic models TextField     output of LearningObjective objects all      lt LearningObjective  lO1 gt    lt LearningObjective  lO2 gt    lt LearningObjective  lO3 gt     output of Topic objects all      lt Topic  Topic object gt    lt Topic  Topic object gt    lt Topic  Topic object gt    lt Topic  Topic object gt    lt Topic  Topic object gt    lt Topic  Topic object gt    lt Topic  Topic object gt    lt Topic  Topic object gt    lt Topic  Topic object gt    lt Topic  Topic object gt    lt Topic  Topic object gt    lt Topic  Topic object gt    lt Topic  Topic object gt    lt Topic  Topic object gt     views   def create themen request        new topic Topic topic request POST  topic         new topic save        return render request   topic html     topic   topic objects all       def create learning objective request        new learning objective LearningObjective learning objective request POST  learning objective         new learning objective save        new learning objective topic Topic objects get topic request POST  topic         new learning objective topic new learning objective topic add new learning objective       return render  request   learning objective html                          topic   Topic objects all                         todo   TodoList objects all                         learning objective   LearningObjective objects all

User · Accepted Answer

get   returned more than one topic -- it returned 2    The above error indicatess that you have more than one record in the DB related to the specific parameter you passed while querying using get   such as   Model objects get field name some param    To avoid this kind of error in the future  you always need to do query as per your schema design  In your case you designed a table with a many-to-many relationship so obviously there will be multiple records for that field and that is the reason you are getting the above error   So instead of using get   you should use filter   which will return multiple records  Such as   Model objects filter field name some param    Please read about how to make queries in django here

User · Answer

To add to CrazyGeek s answer  get or get or create queries work only when there s one instance of the object in the database  filter is for two or more   If a query can be for single or multiple instances  it s best to add an ID to the div and use an if statement e g   def updateUserCollection request       data   json loads request body      card id   data  card id       action   data  action        user   request user     card   Cards objects get card id card id       if data-action     add           collection   Collection objects get or create user user  card card          collection quantity   1         collection save        elif data-action     remove           collection   Cards objects filter user user  card card          collection quantity   0         collection update     Note   save   becomes  update   for updating multiple objects  Hope this helps someone  gave me a long day s headache

User · Answer

Get is supposed to return  one and exactly one record  to fix this use filter    and then take first element of the queryset returned to get the object you were expecting from get  also it would be useful to check if atleast one record is returned before taking out the first element to avoid IndexError

User · Answer

In your Topic model you re allowing for more than one element to have the same topic field  You have created two with the same one already   topic models TextField verbose name  Thema     Now when trying to add a new learningObjective you seem to want to add it to only one Topic that matches what you re sending on the form  Since there s more than one with the same topic field get is finding 2  hence the exception   You can either add the learningObjective to all Topics with that topic field   for t in topic objects filter topic request POST  Thema         t learningObjectivesTopic add neuesLernziel    or restrict the Topic model to have a unique topic field and keep using get  but that might not be what you want

User · Answer

Don t  - xyz   Blogs objects get user id id   Use - xyz   Blogs objects all   filter user id id

User · Answer

I had same problem and solution was obj   ClassName objects filter

User · Answer

get   returns a single object  If there is no existing object to return  you will receive  lt class gt  DoesNotExist  If your query returns more than one object  then you will get MultipleObjectsReturned  You can check here for more details about get    queries      Similarly  Django will complain if more than one item matches the get   query  In this case  it will raise MultipleObjectsReturned  which again is an attribute of the model class itself    M2M will return any number of query that it is related to  In this case you can receive zero  one or more items with your query    In your models you can us following   for  topic in topic objects all         topic learningobjective set all     you can use  set to execute a select query on M2M  In above case  you will filter all learningObjectives related to each topic

[django] django - get() returned more than one topic

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