How to get an array of objects with spring #RequestParam in ManyToMany relationship? - spring

Question

I have an entity Movies and an entity Genres in a relationship many to many.
#ManyToMany
#JoinTable(name = "movies_genres", joinColumns = #JoinColumn(name = "movies_id"), inverseJoinColumns = #JoinColumn(name = "genres_id"))
private Set<Genres> genresSet = new HashSet<>();
In a rest controller class, I want to do this:
#GetMapping("/search-movies")
public Iterable<Movies> search(
#RequestParam(value = "genresSet", required = false) Set<Genres> genresSet,
#RequestParam(value = "synopsis", required = false) String synopsis,
#RequestParam(value = "title", required = false) String title,
#RequestParam(value = "runtime", required = false) Integer runtime
)
I use axios on front-end to send params to the back-end and genresSet is array of objects, for example
[
{ id: 1, name: 'action'},
{ id: 2, name: 'crime'},
{ id: 3, name: 'comedy'}
]
I thought that Spring would automatically convert array of objects into set of genres, but it gives me null.
How to get values of genres in form of a set of values?
To recap, the user enters more than one genre, where each genre is represented as an object, so front-end sends array of genre objects and back-end needs to bind that array to the set of genres, where set of genres is a many to many property of Movie entity.

Answer 1

You can rethink your parameters and change Set<Genres> either to Set<Integer> or Set<String>. Because you need just ids or just names of genres to use them in search query, you don't need to pass the whole Genres object.
#GetMapping("/search-movies")
public Iterable<Movies> search(
#RequestParam(value = "genresIds", required = false) Set<Long> genresIds,
// ... other parameters without changes
would accept
"genresIds": [1, 2, 3]
or
#GetMapping("/search-movies")
public Iterable<Movies> search(
#RequestParam(value = "genresNames", required = false) Set<String> genresNames,
// ... other parameters without changes
would accept
"genresNames": ['action', 'crime', 'comedy']

Answer 2

Another way you could accomplish this is to create a wrapper class for the Set. For example:
public class GenresWrapper {
Set<Genres> genresSet;
// ... accessors
}
Then your controller method would look like this:
#GetMapping("/search-movies")
public Iterable<Movies> search(
#ModelAttribute GenresWrapper genres,
// ... other parameters
)
Or you could wrap all the request parameters in a single wrapper object.
This answer is based on another SO answer.