Recently I found no obvious behaviour when using ‘select new/constructor expression’ in jpa/hibernate. It uses kind of lazy loading for each entity in each row in result set what is not efficient. Test example First case we issue a query using select new technique: This issues one query to fetch only ids of e1 and e2 and then more queries
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Tag: orm
Update statement is no query?
How do I define the update statement in the orm.xml. I have it as a named-query and everything works, but my teacher said that an update statement isn’t a query. I have tried a native query, but that wasn’t working. ORM-Type: Update Statement: Answer The term “query” is used rather ambiguously. Some people interpret it literally as “asking for information”,
Java ORM vs multiple entities
I have a class Health Check – as part of the class I record how many parasites are seen (enum NONE, SOME, MANY) and also the location of the parasites (enum HEAD, FEET, BODY). Two ways this could be done: METHOD 1 Health Check Parasite Or I could have: METHOD 2 Would method 1 require @Entity on parasite class and
NamedQuery returning entities with null fields
defined entity with namedquery as SELECT mdl FROM tbl_slots mdl where mdl.test_date between :dt and :dt order by mdl.test_time asc if used * instead of mdl in query, JPA gives error unexpected token: * if mentioned the column names in select statement it returns entities with respective fields populated with expected values [{ “srNo”: 1, “testDate”: “2021-Dec-30”, “testTime”: “09:00-10:00”, },{
auto changing data with Hibernate
I have problem with Hibernate. I have next method: This method should assign user on task and send message to kafka consumer with TaskBeforeUpdate and TaskAfterUpdate. But I have problem when I try to assign user, my BeforeUpdateTask change all his fields to TaskAfterUpdate. And this dont work, but i dont know why he is change all values. Answer The
JOOQ: How to resolve foreign keys as objects?
Say I have a table that references another table, in this case “TestScenarios” references “TestSchemas”. So each TestScenario HAS-A TestSchema. I autogenerated DAOs, however, when fetching …
How to remove child objects from a @ManyToMany relation with lots of children in JPA and Hibernate
Let’s say I have two entities: Organization and User. Every user can be a member of many organizations and every organization can have many users. @Entity public class User { @ManyToMany Set&…
Android Room Persistence Library : What is the best way to implement a many to many relation?
I used to use Realm and I am currently testing Room in order to compare both tools. I am trying to implement the following many to many relation : Here my Entity classes : The Person : @Entity(…
What is the solution for the N+1 issue in JPA and Hibernate?
I understand that the N+1 problem is where one query is executed to fetch N records and N queries to fetch some relational records. But how can it be avoided in Hibernate?
How to map an immutable collection with JPA and Hibernate
I am using JPA 2.1 and Hibernate as a JPA implementation, and I want to load a relationship as an immutable collection. Let’s take an example of an Employer parent entity that has an employees child collection. What can be done to instruct JPA to load an immutable employees collection? Answer You can use the @Immutable Hibernate specific annotation: Another
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