Visit HATEOAS links of optional entities [duplicate] - spring

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Spring Data ReST ref link omission when null or empty
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Closed 5 years ago.
I developed a Spring Boot, Spring Data REST, Hibernate application that exposes REST endpoints.
A typical response is something like this:
{
"sid": "f6dddaaa-2713-4b92-844b-6f0d3cefad3f",
"createdBy": "admin",
"createdDate": "2018-01-30T15:56:38.417Z",
"lastModifiedDate": "2018-01-30T15:57:53.963Z",
"lastModifiedBy": "admin",
"status": "Annullato",
"number": "51",
"dailyCode": "VS",
"entryDate": "2018-01-30T15:56:00Z",
"exitDate": "2018-01-31T15:56:00Z",
"totalDays": 1,
"standard": true,
"minibus": false,
"schoolTrip": false,
"price": 400,
"fareRow": "Standard",
"fareColumn": "Euro 0 3",
"extSyncCode": null,
"payments": [],
"passengers": 44,
"agency": null,
"paperBlock": null,
"paperReceipt": null,
"payer": null,
"checkedMedia": false,
"checkedLicensePlate": false,
"_links": {
"self": {
"href": "http://localhost:8080/api/v1/tickets/1"
},
"ticket": {
"href": "http://localhost:8080/api/v1/tickets/1{?projection}",
"templated": true
},
"area": {
"href": "http://localhost:8080/api/v1/tickets/1/area"
},
"fareException": {
"href": "http://localhost:8080/api/v1/tickets/1/fareException"
},
"block": {
"href": "http://localhost:8080/api/v1/tickets/1/block"
},
"customer": {
"href": "http://localhost:8080/api/v1/tickets/1/customer"
},
"transitCertificate": {
"href": "http://localhost:8080/api/v1/tickets/1/transitCertificate"
},
"passengersCountry": {
"href": "http://localhost:8080/api/v1/tickets/1/passengersCountry"
},
"refund": {
"href": "http://localhost:8080/api/v1/tickets/1/refund"
},
"fine": {
"href": "http://localhost:8080/api/v1/tickets/1/fine"
},
"hotel": {
"href": "http://localhost:8080/api/v1/tickets/1/hotel"
},
"workShift": {
"href": "http://localhost:8080/api/v1/tickets/1/workShift"
}
}
}
As you can see this entity has a lot of links. These links represent bound entities. Unfortunately some of these entities are optional.
I created a Angular 5 application that consumes my server side API. When I want to display data (let's say the entity shown in the example) I need to get related entities and I've to visit all links. Because not all related entities are mandatories, some of these links return HTTP 404 and the browser display these calls as errors (see the picture).
Is my approach right? Should I visit all these links and consider the 404 response perfectly fine (I think so) even if the browser consided that as an error? Is there a better approach otherwise?

Answer 1

That’s a lot of work to discover a related entity doesn’t exist. HTTP requests are slow. Admittedly they will run in parallel but it still seems inefficient.
Instead, when you load the parent entity, can you check at that time which children entities will be valid? If the child will not be valid then, instead of a link, return null. Or don’t return the value at all.