Thus far I have referred to this repo as a reference for how to structure my repositories in my Spring project which leverages QueryDSL.
The only "shortcoming" of this example for me is that it does not outline how I might write a Repository which uses a chain of more than one OneToMany relationships. Using this repository as an example/reference, they have a "Customer" repository and for each Customer there are many "Address". I'm unsure how I would use give or take the same patterns they are using, but for a Class which had a OneToMany relationship with Customers. Meaning, how would I handle a Repository for "CustomerGroup" which has a OneToMany relationship with "Customers" which in turn has a one to many relationship with "Addresses".
Some patterns have occurred to me, but not seem elegant/optimal so I'm looking for anyone with experience or insight as to what might be a nice way of solving this problem.
I very much appreciate any help!
Do you mean in order to write WHERE statements based on the relations?
For example if you want to retrieve all customer groups that contain a customer from a specific country, you can simply call
QCustomerGroup.customerGroup.customer.any().addresses.any().country.eq("Germany")
To make this working to need to add
#OneToMany
private Address addresses;
to the Customer entity.
Related
I've been researching this for a while and still couldn't find a satisfactory answer for my problem.
I have an entity on my postgres DB (product) that has a ManyToOne relationship with another entity (Dun).
Each product may have N duns.
On my PUT endpoint, the desired behavior would be:
Every time I update a product, it replaces all the duns with the ones provided on the endpoint.
Is there any way to handle it automatically by Hibernate/JPA?
In order to make it easier to test and explain the issue, I've uploaded a project on Github on the following link https://github.com/brunapereira/jpaexample
If there's no way to handle it automatically by JPA, what's the best way to solve it with code?
Thanks in advance,
First, you need to remove Duns by product id, then get the product by id, add the new duns then save back.
I have two entities Library and Books which are associated by Hibernate #OneToMany in a spring boot project. Fetching books in a particular library through the getter functions renders a LazyInitialisationException. The solution that I could find was making a query in the Books entity and fetching all the books corresponding to the library-id of the library. So, I was thinking why is oneToMany relationship required if we can just store a key corresponding to library in the Books table.
Simply storing a key doesn't provide any consistency assurances. Also, using defined OneToMany or ManyToOne you can also define the cascade types (you would only need to save the parent entity and then all the children would automatically be saved, in a single transaction).
The quick way to fix your problem would be to use FetchType EAGER, but I would recommend fixing whatever you have misconfigured.
So i have 5 tables as Users,Orders,Products,Ingredients and nutrients,
Each is connected to adjacent table via #ManyToOne annotation.
What i am stuck at is how to find product details of a particular user for a particular order and similarly finding ingredients for a particular product for a particular order for a particular user and similarly for nutrients.
I know i have to declare custom crud methods according to a given syntax and i did so but still the method is not working.
Here is the link to the git repository
https://github.com/Guneet007/API.git
You can use Specification/Querydsl for defining custom criteria. Because we should use more than 3 parameters with AND suffix.
One more issue I have found in your code is that your property name not match with your method findByProductId() it should be findByProduct(Product product). Look same for others too.
https://spring.io/blog/2011/04/26/advanced-spring-data-jpa-specifications-and-querydsl/
Suppose if I have 3 entities - User, Skills, Department
and I have repositories corresponding to all of them - UserRepository, SkillRepository, DepartmentRepository.
I understand that the relation mapping between entities i.e. one-one many-many should be specified in the respective entity classes. The question is I want to use all of the 3 entities in a query. How would I do it? A single repository is associated with only one entity right? So, how/where would I write it?
As there are many different ways to specify queries with Spring Data JPA there are various answers to this.
Maybe you don't have to. If entity A references B and you just want to get the Bs with your A you simply use your ARepository to load As and use object navigation to get your Bs. You might read up on eager and lazy loading for more information about how to control this.
If you want referenced entities in the where condition you can use property paths in your query method names: https://docs.spring.io/spring-data/jpa/docs/current/reference/html/#repositories.query-methods.query-property-expressions
If you are using #Query annotations you can do (almost) whatever you want with JPQL. Among others, you may as well navigate properties to use them in where clauses.
In general, you'd put that query in the matching repository based on the primary entity returned.
I am trying to achieve one to many relationship. I know how to do basic one to many relationship between requestor id and userid.
My question is How to refer gtlUserId(resourceRequestTable) to gtlUserId (User table) as by default spring is mapping gtlUserId (resourceRequestTable) to userId in user table
It has some Ways.
I think you should give a specific way during all project !
As My experience each many to one must be a Drop Down in Client side .
However in your Table ResourceTypeEntity should be drop down inside ResourceRequesTable when value of option is Id[primary Key].
Also Your table not seems good design why two many to one map to same table? it may cause 3NF problem in DB also pay attention Cascade it when Parent Table related to other Parent is not good Design ,Keep it simple with uni Direction Many to One And force user to delete manually parent is better ,CaseCade Delete when Parent has related to other table will make exception handling and testing too hard.
please take a look https://examples.javacodegeeks.com/enterprise-java/spring/mvc/spring-mvc-dropdown-box-example/