HAL clients or examples of accessing HAL API

Question

Question: Any HAL clients or examples of accessing HAL API with admin-on-rest ?

I got started because HAL was mentioned in the first paragraph of the introduction, but now I'm having trouble finding any examples or anyone else using HAL rest client, so I am winding up for now just writing a bunch of simple findAll repositories on top of the already robust existing HAL API.

Answer 1

Adding a more concise answer here that isn't polluted with my thought process now that I've got it all figured out (for anyone's future reference)... Again assuming the HAL API was made with Spring Data Rest.

The four major keys to this integration are:

1. Exposing foreign key attributes in your JPA entities, which is required in several places by admin-on-rest @Column(name="parentEntity", updatable=false, insertable=false) private Integer parentEntityId;
2. Exposing all your entity IDs using RepositoryRestConfiguration.exposeIdsFor( MyEntity.class )
3. Annotate your repositories as @RepositoryRestResource and have them extend PagingAndSortingRepository<MyEntity, Integer>, QueryDslPredicateExecutor<MyEntity> to expose extremely useful search filters by attribute name (e.g. /api/myEntitys?field1=foo&field2=bar).
4. When submitting create and save requests with foreign keys make sure to adjust your params.data to include the linked resource (e.g. 'http://myserver.com/api/myEntitys/19') on top of (or in place of, HAL has no use for it) the foreign key you exposed in 1. (e.g. myEntityId=19)

Other small items of note:

use PATCH instead of PUT when updating (you may be able to use PUT if you are more of a hibernate expert and can map your entities better than I can but I had trouble getting it mapped perfectly and HAL's PATCH will take partial entities)

When submitting GET_LIST and GET_MANY_REFERENCE you get the total number of items and pagination parameters from the 'page' section of the response, and you use 'size' and 'page' query params in your API requests. (so, no need for headers and stuff)

To change the default 'equals' filter for any string entries (from 3. above) to a 'contains' filter, you will have to also extend QuerydslBinderCustomizer<QMyEntity> and provide your own customize method in each of your repositories. For example:

default void customize( QuerydslBindings bindings, QChampion champion ) { bindings.bind( String.class ).first( ( StringPath path, String value ) -> path.contains( value ) ); }

Answer 2

For anyone referencing this in the future, if you happen to be in control of your API through Spring Data Rest you can consider the use of an excerptProjection on every one of your existing repositories that shows an inline version of your entity. This would work if there were absolutely nothing besides admin-on-rest accessing your API.

For my case I am planning on writing a custom projection for every rest resource that has entities and naming it the same thing: "inline". Then in the admin-on-rest restClient, just always asking for the inline projection on every GET_MANY or GET_MANY_REFERENCE request.

This is the best I have at the moment. It's not perfect but for the amount of entities I have it's still many weeks faster than building a CRUD interface from scratch so I highly recommend admin-on-rest.

Answer 3

We don't have any examples for HAL specifically. However, the point of this introduction was that admin-on-rest is backend agnostic.

You can create your own custom rest client by following the documentation. Read the code of existing ones for inspiration.