If you are working on hibernate, getting QuerySyntaxException is very common if there is any issue with the query which you are trying to execute in your code. This QuerySyntaxException is more generic and it would throw different types of error messages based on the issue with the query. In this post I would update my experience on getting the different type of messages and how I have solved them.

QuerySyntaxException : Table is not mapped

I have encountered this exception while using the HSQL databases for running my Spring Data application using Spring Boot. Also this error thrown at the time of using the query methods to write the query in spring data repository.

• Error Message: org.hibernate.hql.internal.ast.QuerySyntaxException: $$table_name$$ user is not mapped [$$query_string$$]
• Problem: This problem occurs only when the table name you have mentioned in the query is not matching with the entity.
• Solution: The table name used in the query is not the one in the real database, it should be the name of the entity class. If you are trying to map to the database table and actual entity class name is different, it would throw this error. Also note that the query string should have the exact case (Uppercase or Lowercase) of the entity class name to work properly.

[code]
Caused by: org.hibernate.hql.internal.ast.QuerySyntaxException: user is not mapped [select username from user u where u.username = ?1]
at org.hibernate.hql.internal.ast.QuerySyntaxException.generateQueryException(QuerySyntaxException.java:96)
at org.hibernate.QueryException.wrapWithQueryString(QueryException.java:120)
at org.hibernate.hql.internal.ast.QueryTranslatorImpl.doCompile(QueryTranslatorImpl.java:234)
Caused by: org.hibernate.hql.internal.ast.QuerySyntaxException: user is not mapped
at org.hibernate.hql.internal.ast.util.SessionFactoryHelper.requireClassPersister(SessionFactoryHelper.java:189)
at org.hibernate.hql.internal.ast.tree.FromElementFactory.addFromElement(FromElementFactory.java:109)
at org.hibernate.hql.internal.ast.tree.FromClause.addFromElement(FromClause.java:95)
[/code]

I hope this solution would solve your problem. Still you have not solved, please post your exception trace in the comments section.

You are here because you have just thrown out by your application with this annoying exception : javax.persistence.PersistenceException: org.hibernate.PersistentObjectException: detached entity passed to persist. There are multiple reasons that could cause this exception. But, basic idea behind this exception is that the object which you are trying to persist is not in the persistant state. Note that this exception will be thrown even if you dont have the transaction enabled in your application.

also read:

• Spring + Primefaces + Hibarnate
• Introduction to Spring OXM

One of the complicated issue while working with Hibernate / JPA projects are that differentiating the state of persistent objects. If you no longer required an object, programatically one can detach an entity from the transaction and it will be no longer in the persistence state.

In many cases, the object would have been considered as detached even though you are not intentionally done that.

1. Check if you are trying to persist an entity which has the same id as another entity, and which is already present in the PersistenceContext in your application.
2. Do not set an ID before you save or persist it. Hibernate will look at the Entity you’ve passed and it assumes that because it has its Primary Key populated that it is already in the database.
3. If you are working with Spring MVC application, check that whether you have added <tx:annotation-driven/> in your configuration file. If you are missing this line, transactions would not have been started in your application. This will ultimately throw exception javax.persistence.PersistenceException: org.hibernate.PersistentObjectException: detached entity passed to persist.

If you are still not able to resolve this issue, please write it in the comments section.