I have a java class that implements serializable and the class begins with :
#NamedQueries( {
#NamedQuery(....)
#NamedQuery(....)
...
..})
My question is at what stage these queries are going to be executed because i see no direct call to these queries by their name
Project is using JPA. I think IBM implementation of JPA...surely not hibernate.
Thank you
Each named query has a name and the query is executed by invoking EntityManager.createnamedQuery().
If the name of the query is based on a constant, you can search the usages of the constant in your project or if it's just a string, you can a text search in your project.
If you don't find any usages, there's a chance that those queries are not used at all, unless there's another framework that is invoking them (by doing something like convention over configuration).
Related
CRUD operations using Spring Boot + JPA + Hibernate + PostgreSQL
Please am new in this topic. Am trying to create a CRUD Api. Everything is ok but i cant get the UPDATE method using the JpaRepository. I dont have error when i build my project.
I try to code a specific createCustomer method into my customerRepository but still not working
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But when i run it with maven i get this error:
Spring data Repository work mostly with method names. It creates query based on the method name. For example in your Repository interface you have a method findByUserId. This will work even if you have not written any query. How ?
spring-data will formulate the query to fetch the field specified after findBy (UserId in your case). But at compile time, it checks whether you are providing a valid field So that it can prepare a proper query. It does so by checking your entity class (Customer in your case) for this field.
Note : keep in mind that field in Entity is called userId but method name in Repository is called UserId.
The reason save, delete methods are working because you are extending JPARepository class(which in-turn extends other classes), which has these methods. So it works out of the box.
But when you write some method which is not there in any of the super class, then spring-data will try to formulate the query on its own as I specified earlier. So when you write a method like updateCustomer which is not in any of the super classes, then it tries to find in the entity class a field with name updateCustomer and it fails since it cannot find and hence the exception.
So if you want to declare or do something like this, you can do this by annotating such method with #Query(....) and providing the right query inside it.
#Query(update customer set ..........)
Customer updateCustomer(Customer customer)
Hope its clear.
I am devloping Spring MVC + spring-data-jpa + Hibernate example. I'm using simple Repository (by extending JpaRepository<T, ID extends Serializable>) pattern to perform querying on DataSource(DS) and get the result. Even I can write any custom query as per my business needs.
While doing research, I find the "querydsl-sql" API. This API uses plugins and need to use QueryDslPredicateExecutor<T> like (by
extending JpaRepository<T, ID extends Serializable>,
QueryDslPredicateExecutor<T>)
. But on high level it look to me that this API also does the same thing that Repository API does.
Could someone please suggest / guide what is the difference between two methods? One use simple Repository and another uses QueryDslPredicateExecutor
List<Customer> findByCustomerNumberAndCustomerId(Integer customerNumber, Integer customerId);
Querydsl method
#Query("select c from Customer c where c.customerNumber=:customerNumber and c.customerId=:customerId")
List<Customer> findByCustomerNumberAndCustomerId(#Param("customerNumber")
Integer customerNumber, #Param("customerId") Integer customerId);
Your Querydsl method example is actually a spring-data repository method.
The difference is that QueryDsl offers a simple and beautiful way to create dynamic queries to database. I.e. it allows to create SQL "on the fly".
This is useful when for example you need to retrieve a collection of entities with a complex filter. E.g. by name, date, cost etc. And resulting SQL should contain only conditions which specified in filter.
Spring data allows to achieve this without Querydsl using built-in Specifications API but Querydsl way is simpler and even more IDE-friendly.
More on this:
https://spring.io/blog/2011/04/26/advanced-spring-data-jpa-specifications-and-querydsl/
When is the implementation for repositories generated by Spring Data? At compile time or runtime? Can I see the implementation repository implementation generated by Spring Data?
tl;dr
No, for a very simple reason: there's no code generation going on. The implementation is based on proxies and a method interceptor delegating the call executions to the right places.
Details
Effectively, a method execution can be backed by 3 types of code:
The store specific implementation of CrudRepository. Have a look for types named Simple(Jpa|Mongo|Neo4|…)Repository (see the JPA specific one here). They have "real" implementations for all of the methods in CrudRepository and PagingAndSortingRepository.
Query methods are effectively executed by QueryExecutorMethodInterceptor.doInvoke(…) (see here). It's basically a 3-step-process to find the delegation target and invoke it. The actual execution is done in classes named (Jpa|Mongo|Neo4j…)QueryExecution (see this one for example).
Custom implementation code is called directly, also from QueryExecutorMethodInterceptor.
The only thing left is the query derivation, which consists of two major parts: method name parsing and query creation. For the former, have a look at PartTree. It takes a method name and a base type and will return you a parsed AST-like structure or throw an exception if it fails to resolve properties or the like.
The latter is implemented in classes named PartTree(Jpa|Mongo|Neo4j|…)Query and delegates to additional components for actually creating the store specific query. E.g. for JPA the interesting bits are probably in JpaQueryCreator.PredicateBuilder.build() (see here).
How can I use the tools to generate DAOs?
In fact, instead of passing through the hbm files, I need to configure hibernate tools to generate the DAO and the annotations.
See Hibernate Tools - DAO generation and How generate DAO with Hibernate Tools in Eclipse?
First let me assume DAO as POJO/Entity beans. Basically you can accomplish your task either through forward or reverse engineering. In case of forward engineering, probably you can look into AndroMDA tool. In case If u wish to accomplish it through reverse engineering Click here ..
Hope this will be helpful.
Welcome. You got to write all your data access logic by your hand (if I’m not wrong). Hiberante let you interact with database in three ways.
Native SQL which is nothing but DDL/plain SQL query. This can be used very rarely in hibernate projects even though this is faster than below mentioned options. Reason is simple “One of the key advantage of hibernate or any other popular ORM framework over JDBC Is you can get rid of database specific queries from your application code!”
HQL stands for hibernate query language which is proprietary query language of hibernate. This looks similar to native SQL queries but the key difference is object/class name will be used instead of table name and public variable names will be used instead of column names. This is more Object oriented approach. Some interesting things will be happening in background and check if you are keen!
Criteria API is a more object oriented and elegant alternative to Hibernate Query Language (HQL). It’s always a good solution to an application which has many optional search criteria.
You can find lots of examples on internet. Please post your specific requirements for further clarification on your problem.
Cheers!
I'm working on my first Scala application, where we use an ActiveRecord style to retrieve data from MongoDB.
I have models like User and Category, which all have a companion object that uses the trait:
class MongoModel[T <: IdentifiableModel with CaseClass] extends ModelCompanion[T, ObjectId]
ModelCompanion is a Salat class which provide common MongoDB crud operations.
This permits to retrieve data like this:
User.profile(userId)
I never had any experience with this ActiveRecord query style. But I know Rails people are using it. And I think I saw it on Play documentation (version 1.2?) to deal with JPA.
For now it works fine, but I want to be able to run integration tests on my MongoDB.
I can run an "embedded" MongoDB with a library. The big deal is that my host/port configuration are actually kind of hardcoded on the MongoModel class which is extended by all the model companions.
I want to be able to specify a different host/port when I run integration tests (or any other "profile" I could create in the future).
I understand well dependency injection, using Spring for many years in Java, and the drawbacks of all this static stuff in my application. I saw that there is now a scala-friendly way to configure a Spring application, but I'm not sure using Spring is appropriate in Scala.
I have read some stuff about the Cake pattern and it seems to do what I want, being some kind of typesafe, compile-time-checked spring context.
Should I definitely go to the Cake pattern, or is there any other elegant alternative in Scala?
Can I keep using an ActiveRecord style or is it a total anti-pattern for testability?
Thanks
No any static references - using Cake pattern you got 2 different classes for 2 namespaces/environments, each overriding "host/port" resource on its own. Create a trait containing your resources, inherit it 2 times (by providing actual information about host/port, depending on environment) and add to appropriate companion objects (for prod and for test). Inside MongoModel add self type that is your new trait, and refactor all host/port references in MongoModel, to use that self type (your new trait).
I'd definitely go with the Cake Pattern.
You can read the following article with show an example of how to use the Cake Pattern in a Play2 application:
http://julien.richard-foy.fr/blog/2011/11/26/dependency-injection-in-scala-with-play-2-it-s-free/