Kotlin:How to add arraylist into an Entity in data class

Question

I am trying to make a facebook clone app . And from the very begining ,I will need to define a user class . And I got stuck here , every users ,supose to have followers list and following list .How do it able to make this model ? Could you please take a look my code ,thank you so much in advance ！！

@Entity(tableName="user_table")
@Parcelize
data class User(
    @PrimaryKey(autoGenerate = true)
    val userId : Int=0 ,
    val username :String,
    val email :String,
    val password : String,
    var followers: Array<User>?,
    var followings: Array<User>?,


) : Parcelable

data class UserResponse(val user:User?)

Also ,I attach my node.js model schema :

const mongoose = require('mongoose');

const router = require("express").Router();

const userSchema = new mongoose.Schema({
    username:{
        type:String,
        required : true,
        min:3,
        max:50,
    },

    email:{
        type:String,
        required:true,
        unique:true
    },
    password:{
        type:String,
        required : true,
    },
    profilePicture:{
        type:String,
        default:''
    },
    coverPicture:{
        type : String,
        default:''
    },
    followers:{
        type:Array,
        default :[]
    },
    followings:{
        type:Array,
        default:[]
    },
    isAdmin:{
        type:Boolean,
        default : false
    }

},
{timestamps:true}
);

const User = mongoose.model('User',userSchema);
exports.userSchema = userSchema;
exports.User = User;

Hi Robin ,it didn't appear error ,just appears something like warning like ,it needs to generate hashcode .And after I follow it ,the warning removed .However ,I am not sure if i have writen in the right format,I post it here for asking opinion from you guys .What do you think ?Any problem my code ? Thank you so much ! — Yellow Clock
– Yellow Clock, Commented Dec 2, 2021 at 20:59
I would use List<User>? rather than Array<User>? because they are easier to use and I would probably remove the ? too because the response defaults to an empty list and not null which is okay in Kotlin so List<User> should just suffice — Robin
– Robin, Commented Dec 2, 2021 at 21:04
Probably a good idea would be to separate your network response models from the database entities. Currently the way this is setup, making a change that does not concern the DB will force you to migrate — Robin
– Robin, Commented Dec 2, 2021 at 21:08

Anshul · Accepted Answer · 2021-12-03 03:56:15Z

1

The first thing you should do is to change

var followers: Array<User>?,
var followings: Array<User>?

To

var followers: Array<Int>?,
var followings: Array<Int>?

Int may be the type of your userId or make it to String By doing this you will not be recursively fetching your whole database and looping for getting followers and following.

And if you are using Room to store your data , add TypeConverters.

answered Dec 3, 2021 at 3:56

Anshul

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