I want to learn more about Spring JPA and what happens under the hood when a native JPA query (using PostgreSQL) is defined and called in a Repository class. I have tried searching online but all posts are related to defining and using native queries.
I am more interested to learn about what happens when my SpringBoot application calls a method that is annotated with #Query. I am mainly looking into this to try and understand the performance of executing such a query within Java.
Can anyone point me to a resource which goes in depth on what exactly happens under the hood when using Spring JPA?
Can anyone point me to a resource which goes in depth on what exactly happens under the hood when using Spring [DATA] JPA?
The authoritative source for this kind of information is the source.
Let me point you to some places of interest.
Basically the following happens:
find and extract the query from the annotation.
possibly create a count query from that.
replace spell expression with parameters.
add ordering if applicable.
prepare the query with the EntityManager.
register parameters.
add pagination limits.
execute the query.
transform result.
Output log to view what SQL query really generated and executed
For example, in application.properties:
logging.level.org.springframework.data.jpa=debug
logging.level.org.hibernate=debug
SpringBoot log reference
Check the source code of spring-data-jpa here:
https://github.com/spring-projects/spring-data-jpa/blob/master/src/main/java/org/springframework/data/jpa/repository/query/JpaQueryExecution.java
Related
I am new in Spring data JPA and when I am searching I also read Spring Data JPA #Modifying Annotation and why do we have to use #Modifying annotation for queries in Data Jpa.
After reading the accepted answer on SO page, I am confused. Now, could you pls clarify me about the following issues?
1. Should we still need to use #Modifying Annotation in the last version(s) of Spring Data JPA? If so, could you explain how should I use properly (any annotation for proper usage)?
2. I am also wondering if the similar issue is valid for #Transactional annotation? Should we also need to use it for the create, update and delete methods in Spring Boot service methods? If so, could you also give a proper usage examples for an example scenario?
from what i understand from the references, yes you have to use #Modifying for an Insert/create/delete ddl query. And you have to use #Modifying(clearAutomatically=true, flushAutomatically=true) if you are doing more update/modifying operations before or after another update/modifying operations. In the given SO he clearly stated whats happening if you are not using those two flags.
#Transactional should use for the service method/ business method. if you execute set of selections, updates, deletion in one business logic, those will be grouped and one persistence context will be used for them. so your micro query changes are visible to other micro queries with in the transaction(there can be many micro queries in your business logic code). Even if you use those above flags without using #transaction those changes wont visible to other micro queries as its work in different transaction level and which will fail your business logic .
After making some search on the web, I think that when using Spring Data JPA Named Queries, we need some extra implementation or definitions comparing to the derived or dynamic queries in Spring Data JPA. In this scene, I am really wondering that do we really need to use Spring Data JPA Named Queries?
Spring Data derived queries are intended (and useful) only for very simple queries. Those queries where you look at the name that you would naturally give such a method and would immediately know how to implement it in SQL or JPQL.
As soon as a query gets a little more complex we shouldn't use derived queries anymore, and often we can't even if we wanted to. For example query derivation doesn't have a way to control the precedence between AND and OR.
For all other queries we need to explicitly code the query one way or the others. And if you don't want your queries mixed with your repository, a named query is a very viable alternative.
I am looking for a way to call function that returns ref cursor without using entity.
I found a way by using CollableStatement. if my spring boot app does not have any other entity to be handled, does it make sense not using jpa at all? and just use java.sql? meaning just connect and execute collablestatement query?
If there is any better way or my understanding is incorrect, please guide.
Thanks!
I don't think it makes sense to use JPA in your case.
JPA is mainly about CRUD functionality and it seems you are not using any of that.
I recommend to take a look at Springs JdbcTemplate, it probably fits your needs much better.
I want to implement a search function with five optional variables and in every combination, so a switch/case is not a possible way. So i can't use the build in spring boot functions, because they are not dynamic (correct me if i'm wrong).
I know there is the #query annotation in the crudrepository, but there is no way to write a query with optional parameters?
I tried to write my own database access with jpa, without the help of spring boot CrudRepository.
I read in the manual this should work:
#Autowired
#PersistenceContext
private EntityManager em;
#Transactional
public List<Persons>searchPersons(params...){}
But here is the problem, my EntityManager is always null and i have no idea why. I searched some hours and found nothing.
Maybe you guys know a way to write a dynamic SQL query in Spring Boot.
Is there a way in the CrudRepository to define optional parameters for the query?
Btw i use a postgreSQL database.
Many thanks for your help.
You might want to have a look at Specifications.
See the documentation here
For that to work, your repository interface needs to implement JpaSpecificationExecutor.
You can use a custom repository (create your own interface, write one Impl class for it and extend your repository by that interface.
You should then have:
PersonRepositoryCustom
PersonRepositoryCustomImpl
Next, you implement a query, using the EntityManager autowired into your repository. You can do this by using JPQL or the JPA 2.1 Criteria API.
For each parameter, have a condition to add it to the query itself, as well as the prepared statement parameters. That way, you can build a dynamic query.
The following thread is related:
Best way to create JPA query that might contain a parameter or might not
I know this question is old but to anyone coming here interested in implementing dynamic SQL queries, check out these two blog posts, they are great.
Implementing dynamic SQL queries using Spring Data JPA
Specification and Criteria API
Writing dynamic SQL queries using Spring Data JPA repositories and
EntityManager
I'm using Spring's JDBC support to run SQL queries and updates on an Oracle database. I'd like to insert a row and then get the key that it was assigned (using an Oracle sequence). In normal JDBC code, I would include a RETURNING INTO clause and then register an output parameter (well described here)
However, I would like to just use Spring to handle all my JDBC work for me. For non-insert SQL statements, I'm currently using a MapSqlParameterSource object and registering all my input parameters. Can I also register an output parameter like this and have it returned to me? I looked over the Chapter 11 portion of the Spring docs, and I saw there was support for an output parameter if I'm using stored procedures, but I would like to avoid doing that if possible. Thanks.
I don't think the Spring JDBC support API provides explicit support for OUT parameters, so you may need to step back a bit and use the more general query API provided by JdbcTemplate:
Object execute(PreparedStatementCreator psc, PreparedStatementCallback action)
This lets you perform arbitrary JDBC operations within the scope of a Spring-managed connection and PrepatedStatement. The downside is that the handling and tidyup of things like ResultSets becomes your problem.
Check out this code - it may do what you want, not sure if Oracle supports this syntax though.
getReturnedGeneratedKeys() Spring JDBC Excample