Android room database delete is not working?

Question

I made some simple project for test, but i'm having some trouble with delete. It won't work. I can add contact normally, but when I try to delete it, nothing happens and i don't have any erros. Here is my code:

Entity

@Entity
public class Contact {

    @PrimaryKey(autoGenerate = true)
    private int id;

    @ColumnInfo(name = "contact_name")
    private String contactName;

    @ColumnInfo(name = "contact_number")
    private String contactNumber;

    @ColumnInfo(name = "contact_image")
    @Nullable
    private String contactImage;

...

My Dao:

@Dao
public interface ContactDao {

    @Query("SELECT * FROM Contact")
    LiveData<List<Contact>> getContacts();

    @Query("SELECT * FROM Contact WHERE id = :contact_id")
    Contact getContactById(int contact_id);

    @Insert
    void addContact(Contact contact);

    @Delete
    void deleteContact(Contact contact);
}

ViewModel:

public class ContactViewModel extends AndroidViewModel {

    private LiveData<List<Contact>> contacts;
    private ContactsDatabase contactsDatabase;

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

        contactsDatabase = ContactsDatabase.getINSTANCE(this.getApplication());
        contacts = contactsDatabase.contactDao().getContacts();
    }

    public LiveData<List<Contact>> getContacts() {
        return contacts;
    }

    public void deleteContact(Contact contact) {
        new deleteAT(contactsDatabase).execute(contact);
    }

    private class deleteAT extends AsyncTask<Contact, Void, Void> {

        private ContactsDatabase contactsDatabase;

        deleteAT(ContactsDatabase db) {
            this.contactsDatabase = db;
        }

        @Override
        protected Void doInBackground(Contact... contacts) {
            contactsDatabase.contactDao().deleteContact(contacts[0]);
            return null;
        }
    }
}

Any solutions ?

Answer 1

In some cases it might be better to add a custom delete by-id instead of using the auto-generated delete by-object.

In this case it'd be

    @Query("DELETE FROM Contact WHERE id = :contact_id")
    void deleteContactById(int contact_id);

See https://stackoverflow.com/a/47554641/6513193 for more info.