I'm using JPA and Hibernate for my Spring Project.
I created my db/entities and for some specific API I would like to improve my queries.
I think that for these, only for these specific scenarios, I need to use some joins. So, in practically, I need to have a different fetch mode (from LAZY to EAGER).
Is there a way to specify the fetch mode into my JPA repository for a specific method? Or have I to write the JPQL queries (or Criteria queries)?
You can use Named entity graphs to control fetch mode in any level of the object graph.
Related
I have a CRUD based application, which uses Spring Boot REST Services and JPA. For JPA we have POJO objects mapped to RBMS - PostgreSQL.
Some of my pages require data to be fetched using joins of multiple POJO objects. I just wanted to know what is a good architectural practice to do the same. Following are some of the options i have been informed of, but not sure what are the pros and cons of each especially for a large data volume application.
Use Transient Variables in POJOs and use JPA joins
Use additional Spring View Objects to combine POJOs
Write native/HQL to join tables/POJOs
Any insight would be helpful. If any more details required from me, would be glad to provide.
I think it's better to go with Entity Mappings.
This will enable you to easily fetch the parent and its nested entities using either JPA methods or using hibernate.
You can also specify the fetch type to actually control the behaviour of this fetch.
In case, you are looking for any complex joins or fetch patterns, Entity Graphs and HQL will be very useful.
I would like to know why we are using spring jpa specifications in spring boot application. I could see something like specifications (classname).and , .or these kind of operations what exactly it is?
Spring JPA specifications allow you to define a predicate (a part of WHERE clause of a query).
This helps you create complex queries in an object oriented style, allow you to create reusable predicates that you may use in different queries without repeating yourself, and it can help you create dynamic queries that can be constructed at runtime.
One example of a good use case for specifications is a search page with optional filtering criteria (think any eCommerce website). Using JPA specifications you can define a predicate for each filter and at runtime you can include in your query only the predicates that are related to the filters that the user has applied.
I have to use SOQL queries within a Spring Data Repository, Is there a way to do so by using #Query annotation ? If not is there a alternative way ?
As far as I know salesforce doesn't expose the table structures. Rather they expose their objects and you can write queries on them. spring-data-jpa is used on top of an entity framework like hibernate. Unless you have entity objects mapped to actual database tables, spring-data-jpa is not useful.
The best way would be to use a query builder like jooq and construct SOQL queries easily using query builders.
JPA #NamedQuery is translated to SQL only once when application is deployed and generated SQL is cached.
EntityManager.createQuery translates query every time our method is called.
What Spring-data-jpa is doing with query defined in #Query annotation? Is it translated to SQL once during deployment (like NamedQuery) or translated every time (like dynamic query) ?
Spring Data JPA calls EntityManager.createQuery(…) for every invocation of a query method annotated with #Query. The reason for that is quite simple: the Query instances returned by the EntityManager are not thread-safe and actually stateful as they contain bound parameter information.
That said, most of the JPA persistence provider perform some kind of text-based query caching anyway so that they basically build the actual SQL query once for a certain JPQL query and reuse the former on subsequent invocations.
As an interesting side note, when we started building the support for #Query in 2008 we looked into possibilities to rather register the manually declared queries as named queries with JPA. Unfortunately there wasn't - and up until today - there's no way to manually register a named query programmatically via the JPA.
We are using the Spring Data JPA for database access. Our repositories contain basic query methods. What we want to do now is to use the Specification-Interface (criteria API) combined with complex query methods (like findByName(Specification spec)). The problem is that these two ways block each other out (since there are two where queries now). Is there any way to do this, like telling JPA to combine the two where parts with AND? The reason we want to do this is because some parts of the where query are essential for every query. They should be defined in the name of the query method. The Specification only should contain individual criterias for individual use-cases.
Or is there any other way to solve this?
Currently this is not supported. Please feel free to raise a JIRA issue if you think this would be a worthwhile enhancement.