findAll(ListU ..) in spring jpa is called by passing UUID's list of size n, when sql logs are enabled i found n number of sql getting logged ,which i assume DB is being called n times(size of list) to fetch records.
can it be possible to call DB only once to fetch all the records at once so that performance can be improved
Spring Data uses an IN close for this method except when your entity has a composite key. That is already just one query.
So the multiple queries you see is most likely your JPA implementation deciding to return a proxy with just the id and then lazy loading the attributes by demand. See the documentation of the implementation you are using for how to prevent/control that.
Related
I'm using Spring Data JPA to expose REST APIs. In my application, there are two types of tables available(current and archival) and structure of the current and archival tables are exactly similar and data will be moved for current table to archival table over the period of time for performance reasons. I'm having repository classes to retrieve the data from current and archival table separately and Pagination is also implemented for repositories.
Now I got a requirement to fetch the eligible records from both tables based on criteria and apply pagination at single shot. Is it possible with Spring Data JPA
You can keep the latest version in both tables and when you search for data you just do a regular search.
Another option would be to create a view over the two tables.
I also think Hibernate Envers was able to do that though I never tried it.
I'm using Spring boot 2.3, Spring Data REST, Spring HATEOAS, Hibernate.
Let's think to a simple use case like an user creating an invoice in a web client, or a inventory list for a warehouse. When the user submit the form, could be sent hundreds or rows and these rows can have links to other entities.
In the case of the invoice, for example, each row can have a product reference that will be passed to the sever as a link.
That link is translated by Spring into an entity using Repository. My point is that for every row, a query to get the product runs.
This means that everything will be really slow during insert (n+1 select problem).
Probably I missed somthing in the logic, but I didn't see concrete examples that focus on how to handle a big quantity of translations link -> entity.
Do you have any hint about it?
Is your point about many entities that will be created if linked entities will be returned to server? Hibernate (as well as spring) has lazy loading mechanism - https://blog.ippon.tech/boost-the-performance-of-your-spring-data-jpa-application/, so only necessary entities will be populated. Please, correct me if I miss understand your questions.
I have a database and in that database there are many tables of data. I want to fetch the data from any one of those tables by entering a query from the front-end application. I'm not doing any manipulation to the data, doing just retrieving the data from database.
Also, mapping the data requires writing so many entity or POJO classes, so I don't want to map the data to any object. How can I achieve this?
In this case, assuming the mapping of tables if not relevant, you don't need to use JPA/Hibernate at all.
You can use an old, battle tested jdbc template that can execute a query of your choice (that you'll pass from client), will serialize the response to JSONObject and return it as a response in your controller.
The client side will be responsible to rendering the result.
You might also query the database metadata to obtain the information about column names, types, etc. so that the client side will also get this information and will be able to show the results in a more convenient / "advanced" way.
Beware of security implications, though. Basically it means that the client will be able to delete all the records from the database by a simple query and you won't be able to avoid it :)
I am working on a Java 8 / Spring Boot 2 application and I have noticed that the security module of my app internally uses the findByEmail method of my UserRepostiory (which is a standard Spring Data JPA Repository). When I enabled Hibernate SQL logging, I discovered that these queries are performed multiple times within the same session (security uses it 3-4 times and then my business code uses it some more times). Each time the query hits the database.
This surprised me, as I expected it to be cached in the Hibernate's first level cache. After reading up about it a little bit more, I found out that the first level cache only caches the result of the findById query, not others.
Is there anyway that I can cache the result of the findByEmail query in the first level cache? (I don't want the cache to be shared between sessions, I don't want to use the 2nd level cache, as I think it should be invalidated right after the current session ends).
Yes, you can cache the results of a query on a unique property if you annotate the property with the #NaturalId annotation. If you then use the dedicated API to execute the query, the results will be stored in the 1st level cache. An example:
User user = entityManager
.unwrap(Session.class)
.bySimpleNaturalId(User.class)
.load("john#example.com");
I am looking to retrieve a large dataset with a JpaRepository, backed by Oracle
table. The choices are to return a collection (List) or a Page of the entity and then step through the results. Please note - I have to consume every record in this set, exactly once. This is not a "look-for-the-first-one-from-a-large-dataset-and-return" operation.
While the paging idea is appealing, the performance will be horrible (n^2) because for each page queried, oracle will have to pull up previous n-1 pages, making the performance progressively worse as I get deeper in the result set.
My understanding of the List alternative is that the entire result-set will be loaded in memory. For oracle JPA spring does not have a backing result-set.
So here are my questions
Is my understanding of the way List works with Spring Data correct? If it's not then I will just use List.
If I am correct, is there an alternative that streams Oracle/JPA result-sets?
Is there a third way that I am not aware of.
Pageable methods in SDJ call additional select count(*) from ... every request. I think this is reason of the problem.
To avoid it you can use Slice instead of Page as return parameter, for example:
Slice<User> getAllBy(Pageable pageable);
Or you can use even List of entities with pagination:
List<User> getAllBy(Pageable pageable);
Additional info