在我的应用程序中，我使用房间作为数据库缓存。我正在使用改造库从服务器获取数据，并将数据保存在房间数据库中，并在回收器视图中显示来自房间的相同数据。

问题：每当活动开始时，它都会从服务器获取数据并将其保存在房间数据库中，因为相同的数据在回收器视图中显示多次。

我想要什么：我想知道如何检查房间中已经存在的数据是否不应该在房间中保存多次时间，如果服务器上更新了一些新数据，它应该获取新数据并将其保存到房间数据库中。

这是我到目前为止所做的：

UserDao.java

@Dao
public interface UserDao {

@Insert(onConflict = OnConflictStrategy.REPLACE)
void Insert(User... users);

@Query("SELECT * FROM Users")
LiveData<List<User>> getRoomUsers();

}

User.java

@Entity(tableName = "Users")
public class User {

@PrimaryKey
private String id;

@ColumnInfo(name = "name")
@SerializedName("name")
@Expose
private String name;

@ColumnInfo(name = "age")
@SerializedName("age")
@Expose
private String age;

public User(String id,String name, String age) {
    this.id = id; 
    this.name = name;
    this.age = age;
}

public String getId() {
    return id;
}

public void setId(String id) {
    this.id = id;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public String getAge() {
    return age;
}

public void setAge(String age) {
    this.age = age;
}
}

UserRepository.java

public class UserRepository {

private Context context;
private UserDb userDb;
private LiveData<List<User>> listLiveData;

public UserRepository(Context context) {
    this.context = context;
    userDb = UserDb.getInstance(context);
    listLiveData = userDb.userDao().getRoomUsers();
}

public void getUserList(){

          Retrofit retrofit = RetrofitClient.getInstance();
          ApiService apiService = retrofit.create(ApiService.class);

          Call<List<User>> userList = apiService.getUser();

          userList.enqueue(new Callback<List<User>>() {
              @Override
              public void onResponse(Call<List<User>> call, final Response<List<User>> response) {

                  Completable.fromAction(new Action() {
                          @Override
                          public void run() throws Exception {

                              if(response.body() != null) {

                                  List<User> list = response.body();

                                  for (int i = 0; i < list.size(); i++) {

                                      String names = list.get(i).getName();
                                      String age = list.get(i).getAge();
                                      String id = UUID.randomUUID().toString();


                                      User user = new User(id,names,age);

                                      userDb.userDao().Insert(user);
                                  }

                              }

                          }
                      }).subscribeOn(Schedulers.io())
                        .observeOn(AndroidSchedulers.mainThread())
                        .subscribe(new CompletableObserver() {
                            @Override
                            public void onSubscribe(Disposable d) {

                            }

                            @Override
                            public void onComplete() {

                                Toast.makeText(context,"Data inserted",Toast.LENGTH_SHORT).show();
                            }

                            @Override
                            public void onError(Throwable e) {

                                Toast.makeText(context,e.getMessage(),Toast.LENGTH_SHORT).show();
                            }
                        });


              }

              @Override
              public void onFailure(Call<List<User>> call, Throwable t) {
                  Toast.makeText(context,t.getMessage(),Toast.LENGTH_LONG).show();
              }
          });

}

public LiveData<List<User>> getRoomUsers(){

    return listLiveData;
}
}

UserViewModel.java

public class UserViewModel extends AndroidViewModel {

private UserRepository repo;
private LiveData<List<User>> listLiveData;

public UserViewModel(@NonNull Application application) {
    super(application);

    repo = new UserRepository(application);
    listLiveData = repo.getRoomUsers();

}

public LiveData<List<User>> getListLiveData() {
    return listLiveData;
}
}

MainActivity.java

public class MainActivity extends AppCompatActivity {

UserRepository userRepository;
RecyclerView recyclerView;
UserViewModel userModel;
List<User> userList;
UserAdapter adapter;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Toolbar toolbar = findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    userRepository = new UserRepository(this);
    userModel = ViewModelProviders.of(this).get(UserViewModel.class);

    recyclerView = findViewById(R.id.recyclerView);
    recyclerView.setHasFixedSize(true);
    recyclerView.setLayoutManager(new LinearLayoutManager(this));

    userList = new ArrayList<>();

    adapter = new UserAdapter(userList,this);
    recyclerView.setAdapter(adapter);

    userModel.getListLiveData().observe(this, new Observer<List<User>>() {

        @Override
        public void onChanged(List<User> users) {
            adapter.setUserList(users);
        }
    });

    FloatingActionButton fab = findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Intent i = new Intent(MainActivity.this,AddUser.class);
            startActivity(i);
        }
    });

    userRepository.getUserList();
}

在MainActivity.javauserReposory. getUserList（）从服务器获取数据并将其保存在房间数据库中。

有人请告诉我如何才能得到想要的结果。任何帮助都将不胜感激。

谢谢