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
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 .
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
I'm writing a library that wraps the JpaRepository interface of Spring Data Jpa because I want to add the same criteria automatically to all JpaRepository DB calls (something like and where t > something).
For example findById function of JpaRepository under the hood will be translated to find by id and where t > something
Is it possible? and if so, how do I do it?
Thanks!
A long time ago this was planned, but the team came to the conclusion that it really doesn't seem possible to do it properly. So No, the feature does not exist. See here for details: https://jira.spring.io/browse/DATACMNS-293
There is Hibernates #Where and #Filter though.
I am planning to use PagingAndSortingRepository interface methods and wanted to understand how do we specify what query to run on calling the method such as findAll?
I'm assuming JPA, but other stores work the same or in case of annotating the entity model similar.
Normally you don't. Spring Data figures out these queries on your behalf. If you want a different query to be executed than the one Spring Data picks, you have the usual choices for custom methods in Spring Data:
If you only need to change table or column names you can annotate your entity model.
provide a #Query annotation.
provide a complete custom annotation.
Actually, I'm new on spring Boot but I've been using Spring for a little while. With spring, I used to handle my database(MySQL) through a generic DAO with hibernate/JPA. However all the tutorials I found on spring Boot use spring data jpa making, therefore, configurations easier.
Thus I would like to know whether it is or not a good idea to keep using my old generic DAO, as it allows me to have the full control and to customize my data access as I want. If yes, how can I proceed? If not, what can be the disadvantages?
The DAO pattern is the same as the Repository Pattern that Spring Data supports. At least, it should be. You have one DAO (=Repository) class per entity that provides methods to query or manipulate that entity.
whether It is or not a good idea to keep using my old generic DAO, as
it allows me to have the a full control and to customize my data
access as I want.
Spring Data is flexible enough to allow full control over your queries. You have the following options (code examples copied from the Spring Data reference):
Using method names: You can simply name your repository methods like this to let Spring Data auto-generate a query for you:
List<User> findByEmailAddressAndLastname(String emailAddress, String lastname);
Using custom queries per annotation: Provide a custom JPAQL query within a #Query annotation
#Query("select u from User u where u.emailAddress = ?1")
User findByEmailAddress(String emailAddress);
Using named queries: define a named JPAQL query within an xml file and reference it within the #Query annotation
<named-query name="User.findByLastname">
<query>select u from User u where u.lastname = ?1</query>
</named-query>
#Query(name="User.findbyLastname")
List<User> findByLastname(String lastname);
Implement a repository method yourself: provide part of the implementation of a Spring Data repository yourself by accessing the Hibernate session (or that of another JPA provider) yourself.
So, to answer your question: yes, use Spring Data JPA, especially on new projects! It does so much work for you and you can still control queries as you wish (which should only be necessary for complicated queries, and even for those I would suggest using programmatic Specifications).
Spring Data JPA will make your life as a developer easier. The DAO pattern is very similar to the Repository Pattern. The advantage of using Spring Data JPA is that you’ll be writing a lot less code. Spring Data JPA works a lot like Spring Integration Gateways, where you define an interface, and Spring provides the implementation at run time.