I've a SQL Query which returns one to many mapping data, for example I've JOB table along with multiple one to one dependent tables and a Warning Table with one-many mapping.
JOB 1 can have n number of warnings to it.
Right now we are handling it from Java logic but Is it possible to achieve it using JPA Native Query?
I see the same scenario's mentioned before How to map native sql results to oneToMany field with SqlResultSetMapping in JPA
This is the exact thing I'm looking for ? Will the Entity take care when used with native Query?
Related
I am reading data from a table using Spring JPA.
This Entity object has one-to-many relationship to other six tables.
All tables together has 20,000 records in them.
I am using below query to fetch data from DB.
SELECT * FROM A WHER ID IN (SELECT ID FROM B WHERE COL1 = '?')
A table has relationship to other 6 tables.
Spring JPA is taking around 30 seconds of time to read this data from DB.
Any idea to improve the data fetch time here.
I am using native Queries here and i am looking for query rewriting that will optimize the data fetch time.
Please suggest thanks.
You might need consider below to identify the root cause:
Check if you are ending up with n+1 query issue. Your query might end up calling n queries for each join table, where n is no. of associations with the join table. You can check this by setting spring.jpa.show-sql=true
If you see the issue as n+1 then you need set appropriate FetchMode, refer https://www.baeldung.com/hibernate-fetchmode for detailed explanation of using different FetchModes.
If it is not n+1 query issue you might need to check the performance of the genarated queries using EXPLAIN command. Usually IN clause on a non indexed columns have performance impact.
So set spring.jpa.show-sql=true and check queries generated and run to debug and optimize your code or query.
I use Spring Data JPA (hibernate) generated queries for fetching data from my Sqlserver. Now i am getting performance related issues in my system.
Load findByLoadId(Integer loadId);
This is the query i am using to get data. This query returns 25 cell data but i only use 5 data from that.
can i use direct native query like
select id,date,createdBy,createdOn,loadName from Load where
loadId=:loadId
but if native query is suggestable then I am having question like Does ORM frameWork reduce performence by getting unneeded data from Database?
By "data cell" I assume that you are referring to database table columns, and not to records. The answer to your question is that yes, ORM frameworks might tend to just do a SELECT * under the hood, which can result in unwanted information being sent across the network to your application. If the JPA repository interface is behaving this way, you may switch to either an explicit JPA query (e.g. using the #Query annotation), or even a native query. Then, just select the columns you want. The issue here is that ORM frameworks map object templates (e.g. classes) to entire database tables. So, the concept of entity implicitly includes every database column. If you go with the option of selecting only certain columns, you may need to do some juggling on the Java side. Note that if the use a JPA query, your code would still, in theory, be database independent.
I'm getting NonUniqueObjectException in hibernate.
There is one Item class, I saved list of Item objects using session.save of hibernate.
Now in the same transaction, I'm trying to update same Items using raw sql query which has join with another table. This gives me NonUniqueObjectException. The two tables I'm joining are unrelated as entities for hibernate, that is, there is no foreign key relation.
So I have 2 questions:
First, is there any way of using hql for writing inner join queries in hibernate.
Second, how to avoid NonUniqueObjectException.
One of the things that is working is that I clear the session before making any raw sql query. Any better approach is welcomed.
I am stuck with an issue. I have 3 tables that are associated with a table in one to many relationship.
An employee may have one or more degrees.
An employee may have one or more departments in past
An employee may have one or more Jobs
I am trying to fetch results using named query in a way that I fetch all the results from Degree table and Department table, but only 5 results from Jobs table. Because I want to apply pagination on Jobs table.
But, all these entities are in User tables as a set. Secondly, I don't want to change mapping file because of other usages of same files and due to some architectural restrictions.
Else in case of mapping I could use BatchSize annotation in mapping file, which I am not willing to do.
The best approach is to write three queries:
userRepository.getDegrees(userId);
userRepository.getDepartments(userId);
userRepository.getJobs(userId, pageIndex);
Spring Data is very useful for pagination, as well as simplifying your data access code.
Hibernate cannot fetch multiple Lists in a single query, and even for Sets, you don't want to run a Cartesian Product. So use queries instead of a single JPQL query.
I was reading the Hibernate HQL tutorial and found that HQL doesn't support INSERT INTO..VALUES.. but INSERT INTO..SELECT.. i.e. HQL only support insert from another table.
Suppose I want to insert same values in one table and that data is not from any other table i.e. the values are not in any other table.Then how can I do that in HQL?
Also, would like to know the rational behind such restrictions in HQL?
You don't need to use hql to insert if the data is from another table.
Simply get a reference to your entity, get a hold of a Hibernate session, and call save().
According to http://docs.jboss.org/hibernate/orm/4.0/devguide/en-US/html/ch04.html#d0e2116
Pseudo-syntax for INSERT statements
INSERT INTO EntityName properties_list select_statement
Only the INSERT INTO ... SELECT ... form is supported. You cannot specify explicit values to insert.
Hibernate is an ORM framework (Object-Relational Mapping).
Its job is that you give objects (Entities) to it and he manages the storage (through Session.save(), IIRC).
So, you do not use the HQL to insert new records, but use the ORM methods.
And (this is a guess) on the other hand, since loading entities from a table, copying them to other entities and storing them one by one is slow, HQL provides a shortcut to the SQL in the DB just for that specific operation for performance purposes.
You can use session.save(object) to insert data into tables.