Using realm I have setup 2 objects: User and Question.
Each User answers a Question, this is stored in a third object like so:
class Answer : Object {
dynamic var user: User?
dynamic var question: Question?
dynamic var answerText = ""
}
What I need to do, is given a user object and a question object, get the related Answer object. In semi-SQL pseudo-code something like:
SELECT FROM Answers WHERE user = User and question = Question
So...How do I achieve this?
Bonus points if there is a way of not having to fetch the question object and instead use the primary key of that object (i have the user object, but only a question id, so i have to resolve the question object first), so something like:
SELECT FROM Answers WHERE user = User and question.id = Question.id
Also because realm doesn't load the entire object into memory until you need it, I don't think it's capable of that.
Note: I've simplified by problem a little. There is a good reason I have the no primary answer id, so please don't tell me to add one.
You will need to change your User model to include an inverse relationship with Answer. This will automatically include all answers where user equals the current user.
Then you will need to query the users, access their answers property and filter that based on the questions.
I have created these skeleton classes so that I can test the query, I know that your User and Question class might be different, so change the primaryKey and question filter to suit your exact class definition.
class User: Object {
let answers = LinkingObjects(fromType: Answer.self, property: "user")
dynamic var userName = ""
override class func primaryKey()->String {
return "userName"
}
}
class Answer : Object {
dynamic var user: User?
dynamic var question: Question?
dynamic var answerText = ""
}
class Question: Object {
dynamic var title = ""
}
let questionId = ""
let questions = realm.object(ofType: User.self, forPrimaryKey: "userName")?.answers.filter("question.id = %#",questionId)
Related
I have a data coming from webservice. I have same models made in my project. To demonstrate the model let me show a little idea of my model
Model1:
class Standard {
var Id = 0
var standardName = ""
var students : [StudentModel] = nil
}
Model2:
class StudentModel {
var Id = 0
var stdName = ""
var Teacher: [TeacherModel] = nil
}
Model3:
class TeacherModel {
var Id = 0
var Name = ""
}
Now what I am facing is as follow :
I have TeacherModel in DB already, but I dont have student model and standard model instance int he Realm, so it is supposed to save coming student and standard data in Realm. and skip or update TeacherModel in Realm. But right now it is crashing on TeachModel data as one Teacher with same things are already saved in Realm.SO i am looking forward to some sort of method in which it update or just skip saving Item if already exist in the Realm.
Note: These models are just to demonstrate my case, where as I know there are many typos and other thing. Also I did not showed any implementation of Realm over my Models. Its just to show you the things to make you understand.
Well you need to have class func primaryKey() -> String? overriden.
override class func primaryKey() -> String? {
return "Id"
}
And then use realm.write(...) or realm.create(...) functions with update parameter set to true.
want some method like which do update the existing followers, and if not exists do add it to DB and link them to user something like
GETS CRASH OVER append in write block, due to duplicate primary key,
also, it works perfectly if no followers has been added in HKUser Table, once it comes to update it crashes
import UIKit
import RealmSwift
class HKUser: Object{
dynamic var full_name = ""
dynamic var email: String?
dynamic var user_id: String?
let followers = List<HKUser>()
override static func primaryKey() -> String? {
return "user_id"
}
}
I want to update the connection of a user in DB also, so I want to do some thing like
//1. updated the userFollower array with required data
let userFollowers:[HKUser] = []
//2. now need to link it with my user object and update it in db
if let user = realmWrapper.sharedInstance.getUser(forID: id) {
try! realm.write {
//want some method like which do update the existing followers,
//and if not exists do add it to db and link them to user something like
//realm.add(user, update: true)
user.followers.append(contentsOf: followers)
/**********
GETS CRASH OVER HERE,
due to duplicate primary key,
it works perfect if no followers has been added in HKUser Table,
once it comes to update it crashes
**********/
}
}
List<T>.append() method save to the Realm implicitly if the objects are unmanaged. That is why the duplicated primary key exception happens.
To avoid this, you can add or update the unmanaged objects before appending to the List. Then you append the objects to the List.
try! realm.write {
...
realm.add(followers, update: true) // Add or update the objects first
user.followers.append(contentsOf: followers)
...
}
Maybe it's not the case (not enough code in your question to tell) but it looks like you prepare the userFollowers array in step 1 to contain ALL the current followers for that specific user.
If this is the case then you'll end up re-adding all the existing followers not only the new ones, hence the duplicate keys.
I've been learning iOS development for the past three weeks, I'm currently following a course on Udemy so far so good.
However I'm following one of the lectures whereby we build an Instagram Clone.
The instructor is using three arrays which are as follows:
var usernames = [""] // Stores all usernames
var userIds = [""] // Stores all Id's of the given usernames
var isFollowing = [false] // Stores where or not you're following that user
To me trying to keep track of what userId goes with what username using two arrays is basically an accident waiting to happen so I decided to set off and find a more feasible approach. I reverted back to my .Net days and decided to create a list so I went and created a class as follows:
class Users{
var Username : NSString = ""
var UserId : NSString = ""
var Following : Bool = false
}
Now inside my ViewController I make a call to Parse which returns me a list of users and I'm basically trying to loop through the response, and add them to the list class as shown here:
var t = [Users]() // After googling the web, this seems to be the syntax for a list declaration ?
let u = Users()
for object in users{
if let o = object as? PFUser {
u.Username = o.username!
u.UserId = o.objectId!
u.Following = o.IsFollowing!
self.t.append(u)
}
}
print(self.t)
Now when I print this to the console I see the following:
ParseStarterProject_Swift.Users
As I have one user at present, however when I try to loop through T and display the username in the console it doesn't display anything.
for x in t {
print(x.Username)
}
Your basic intuition is correct, it's better to have an array of custom objects, not multiple arrays.
Regarding making it more Swifty, consider your Users type. You might want something like:
struct User {
let username: String
let userId: String
let following: Bool
}
Note,
property names should start with lowercase letter;
Users should probably be called User, as it represents a single user;
we don't generally initialize values to default values like that, but rather specify them in the initializer;
we probably use String not NSString;
if a property cannot change, you'd use let, not var;
properties begin with lower case letters;
Then you can do something like:
var t = [User]()
for object in users {
if let o = object as? PFUser {
t.append(User(username: o.username!, userId: o.objectId!, following: o.IsFollowing!)
}
}
print(t)
Clearly, with all of those ! forced unwrapping operators, you'd want to be confident that those fields were populated for all of those properties.
Using struct is nice because (a) it's a value type; (b) you get the initializer for free; and (c) you can just print them. If you really wanted User to be a reference type (a class), you'd do something like:
class User {
let username: String
let userId: String
let following: Bool
init(username: String, userId: String, following: Bool) {
self.username = username
self.userId = userId
self.following = following
}
}
And if you wanted to be able to just print them, you'd define it to conform to CustomStringConvertible:
extension User: CustomStringConvertible {
var description: String { return "<User; username = \(username); userId = \(userId); following = \(following)>" }
}
With the class, you can feel free to change that description computed property to show it in whatever format you want, but it illustrates the idea.
You are correct in considering that keeping track of what userId goes with what username using two arrays is dangerous, you in the correct direction with your approach.
First, I would just like to suggest that you use correct naming convention:
Classes should be singular (except in very specific cases).
Variable/property names should begin with lowercase.
This would mean that your user class should look like this:
class User {
var username : NSString = ""
var userId : NSString = ""
var following : Bool = false
}
I will keep your existing naming use for the next part. The main problem with your code is that the variable "u" is a object which you create only once and then modify it. You should be creating a new "Users" object for each user instead of modifying the original. If you don't do this you will just have an array with the same user multiple times. This is how your code would look now:
var t = [Users]()
for object in users {
if let o = object as? PFUser {
let u = Users()
u.Username = o.username!
u.UserId = o.objectId!
u.Following = o.IsFollowing!
self.t.append(u)
}
}
print(self.t)
Next you mention that when you print to console you see the text: ParseStarterProject_Swift.Users, that is because Swift does not automatically print a pretty text with the content of your object. In order for it to print something more detailed, your "Users" object would need to implement the CustomStringConvertible. You can see a more detailed answer about that here: how-can-i-change-the-textual-representation-displayed-for-a-type-in-swif.
Lastly, you mention that when you loop trough "t" and display the username in the console it does not display anything. This is caused by one of two things:
Because there are no users being returned from parse, so the "t" array is actually empty. Try print(t.count) to see how many objects are in the array.
Because your "Users" object declares an empty string "" as the default username and the username is not being set correctly when getting the data from the parse. Which means that it IS actually printing something, just that it is an empty string. Try defining a different default value like var username : NSString = "Undefined" to see if it prints something.
Good luck learning swift!
New to Parse backend and coding all together.
Looking to create a "Favorite" function in my app so that users can save products that they like for later by tapping a simply UIButton.
I'm simply trying to figure out how to save the toUser (user whose product post is being favorited) and the fromUser (user who is doing the favoriting) in Parse.
Here is my code:
#IBAction func tagProductButton(sender: AnyObject) {
var favoritePost = PFObject(className: "Tag")
favoritePost["tagger"] = PFUser.currentUser()
favoritePost["productId"] = ??
favoritePost["userTagged"] = ??
favoritePost.saveInBackground()
}
"tagger" = toUser
"userTagged" = fromUser
Thank you in advance! remember, I've only been coding for about a month now
You should set the columns product and userTagged (from the Tag table) as Pointers if they are not already. Don't just use the ID as a String. You will need a reference to the Product (parse object) being tagged, so your code could look something like:
favoritePost["product"] = product
favoritePost["userTagged"] = product["user"]
You may not really need the userTagged field on the Tag table, since the user tagged is probably already attached to the product, but this may may other searches easier.
I'm developing an application for iOS using Swift and chose Realm as a database solution for it. I asked one question about Realm and now I have another.
Suppose we have a schema like this:
class Person: Object {
dynamic var id: String = NSUUID().UUIDString
dynamic var name: String?
dynamic var cars: Car?
class Car: Object {
dynamic var name: String?
I have one class (Person) that contains any number of objects of another class (Car). Car that are "linked" with the Person has some properties in context of that Person (and they can be different for same Car for different Persons or for two similar Cars for one Person). Using List<...>() we can not store such properties for each Item, am I right?
If we use Car only for one Person and only once we can create another class that includes only additional properties for Cars and links them with ID of Person plus ID of Car. But it does't work if we have two similar Cars with different additional properties.
So, how I see the solution. Have one table (class) stores ID of Person, ID of one Car and additional properties for this Car. For another Car for the same Person it has the same Person ID, Car ID (same or not) and another additional properties for this instance of a Car.
There is a problem (and a question that I mean). Having that structure I want to query all Cars from that table with their additional properties that have Person ID equals to some_id. How should I do this? Or maybe what another structure (maybe using List<...>) I should have to achieve such kind of behavior?
What is FastList exactly ?
If you want Items to have a property of Lists collection.
You have to redefine your Realm model. something like this.
class Car:Object{
dynamic var createDate: NSDate = NSDate()
}
class Person:Object{
let cars = List<Car>()
}
and query by predicate like this
let realm = Realm()
var ownedCarsFilterByDate = realm.objects(Person).filter("ANY cars.createDate = '\(date)'")
Edited to updated question
Your solution is to create table class, which has 'Person' , 'Car' and 'Context Attribute'.
Your model would be like this
class PersonAndCarRelation:Object{
dynamic var person: Person?
dynamic var car: Car?
dynamic var contextAttribute = ""
}
and you can query all cars associated with person
let personID = "123456789"
let personAndCarArray = realm.objects(PersonAndCarRelation).filter("person.id == \(personID)")
for personAndCar in personAndCarArray{
let personName = personAndCar.person.name
let carName = personAndCar.car.name
let context = personAndCar.contextAttribute
println("I am \(personName). I have a \(carName) with \(context)")
}