Spring, Question regarding Query on Many-to-Many(Association with Extra Columns) in web development - spring

Question

I have 3 class that using Many to Many relationship in Entity level (herbibate)
They are Teams,Users and TeamUsers.
Since I am using hibernate they are all Fetch Lazy
Team:
Users:
TeamUsers:
and we have 3 interface (using by #Autowired in Service or repo layer) which is:
1.TeamRepository extends PagingAndSortingRepository<Team, Integer>
2.UserRepository extends PagingAndSortingRepository<User, Integer>
3.TeamUserRepository extends PagingAndSortingRepository<TeamUsers, Integer>
And here is the core code for many to many relationship mapping:
Team class:
#OneToMany(mappedBy = "team", fetch = FetchType.EAGER)
private Set<TeamUsers> team_users = new HashSet<TeamUsers>();
User class:
#OneToMany(mappedBy = "user", fetch = FetchType.EAGER)
private Set<TeamUsers> team_users = new HashSet<TeamUsers>();
TeamUsers class:
#ManyToOne(fetch = FetchType.EAGER, optional = false)
#JoinColumn(name = "TEAM_ID")
private Team team;
#ManyToOne(fetch = FetchType.EAGER, optional = false)
#JoinColumn(name = "USER_ID")
private User user;
Now, my questions is, what is the best practice to play around this data?
for example:
1. I need all team information and team member from my DB
In restful controller get mapping function, what should I return? should I use TeamUser repository (or maybe one more service layer) to return findAll()? if do so the data will come as object collection of User and Team right(maybe also contain extra column in that table)? Can Json successfully contain that data?
2. I am on webpage and I want to delete a user from a team.
At this timepoint I know the TeamID and UserID from HTML, when I send the Post request to API, should I get User object by UserID, then get Team object by TeamID, then get(Query) TeamUsers object by giving User object and Team Object? or maybe just query by id(from TeamUsers on html) send to API and simply remove this TeamUsers entity?
I'm new to spring and frontend development and I am much apprecaite for your help!

Answer 1

I would suggest the following
If you want to return all the teams and for each team all its users, you should have a TeamService which call findAll method of Team repository this way you will get a list of Teams and for each team a set with its users. And if instead of that you want all of your users and for each one what are its teams you should do the other way, call the findAll method of User repository
Both solutions will serialize to json without problem as long as the objects have its constructor and getter and setter methods
If you want to delete only the relation between user and team you could have a method in your TeamEntity Spring Data repository like this
long deleteByTeamIdAndUserId(long teamId, long userId);
And spring will create a method to perform this action or you can write the query you like just above the method name to be more specific
#Modifying
#Query("delete from TeamUsers t where t.userId=:userId and t.teamId = :teamId")
long deleteByTeamIdAndUserId(long teamId, long userId);