I would like to use a variable inside a Firestore reference. I have a sub-collections stored on the database per shop and they all have the format 'menu Shop1' or 'menu Shop2'. I have to store it this way otherwise if I use menu alone, the collectionGroup reference points to all the menus and returns them all at once - which is not what I want.
I'm struggling to pass the name of the shop to the collectionGroup reference.
This does not work:
let shopName = String("Shop1")
let collectionRef = String("menu \(shopName!)")
let ref = db.collectionGroup((collectionRef!))
But then this works:
let ref = db.collectionGroup("menu Shop1")
I have tried all the variations I know and it still wont pass the string. Does anybody know how to fix this? I'm guessing its a small tweek!
I would just concatenate the string like so:
let shopName: String = "Shop1"
let refString: String = "menu " + shopName
let ref = db.collectionGroup(refString)
Don't forget the 'space' after "menu"
You could also simplify further like so:
let shopName: String = "Shop1"
let ref = db.collectionGroup("menu " + shopName)
The argument does not need to be hard coded...
There's no need for specifying 'String'
let shopName = String("Shop1")
Just make it
let shopName = "Shop1"
Then this is not correct if the intention is to actually create a ref to a collection
let collectionRef = String("menu \(shopName!)")
it should be
let shopsCollection = db.collection("shops")
or like this
let shopName = "shop1"
let thisShop = "menu " + shopName
let shopsCollectionGroup = db.collectionGroup(thisShop)
But... I am not sure you're using the collectionGroups correctly to start with based on the names you're using.
A collection group consists of all collections with the same ID, so for example you could have a collection group of 'shops' whereas yours is called 'menu Shop1' which would indicate a single shop. Or from the guide a collectionGroup called 'landmarks' which would include landmarks from multiple cities.
Read though the Collection Group Queries guide again to ensure it's being used correctly.
As a side note, please protect your code by handling optionals properly.
shopName!
is bad news is shopName is nil as it will crash you code. See nil-coelescing operators, guard and if statements.
Related
I would like to query a particular child from the array of color hex codes.
Here's a snapshot of my database structure:
How do I query a particular hex code and obtain the entire array of its parent object?
You cannot query whether a specific value exists in a list. This is one of the many reasons why the Firebase documentation recommends against using arrays in the database.
But in this case (and most cases that I encounter), you may likely don't really need an array. Say that you just care about what colors your user picked. In that case, you can more efficiently store the colors as a set:
palettes
-KSmJZ....A5I
"0x474A39": true
"0xbA9A7C": true
"0xDEDEDF": true
"0x141414": true
"0x323E35": true
I did it in a different way,
made a function that does this:
let databaseRef = FIRDatabase.database().reference()
let HEX1 = hex1.text! as String
let HEX2 = hex2.text! as String
let HEX3 = hex3.text! as String
let HEX4 = hex4.text! as String
let HEX5 = hex5.text! as String
let URL = url.text! as String
// First set
let colorArray1 = [HEX2, HEX3, HEX4, HEX5, URL]
databaseRef.child("palette").child(HEX1).setValue(colorArray1)
// second set
let colorArray2 = [HEX1, HEX3, HEX4, HEX5, URL]
databaseRef.child("palette").child(HEX2).setValue(colorArray2)
// third set
let colorArray3 = [HEX1, HEX2, HEX4, HEX5, URL]
databaseRef.child("palette").child(HEX3).setValue(colorArray3)
// fourth set
let colorArray4 = [HEX1, HEX2, HEX3, HEX5, URL]
databaseRef.child("palette").child(HEX4).setValue(colorArray4)
// fifth set
let colorArray5 = [HEX1, HEX2, HEX3, HEX4, URL]
databaseRef.child("palette").child(HEX5).setValue(colorArray5)
so that when I target any of the 5 hexes, it will bring me back the whole array together with it.
I'm comparing the characters contained within two words. In seeking to accomplish this, Set (aka NSSet) seemed like the way to go to accomplish this task. I've discovered it returns false positives on matches, so I am attempting to use CountedSet (aka NSCountedSet) instead.
I'm able to initialize a Set without issue, but I can't get the CountedSet initializer to work. Here's what I've done...
I start with a String:
// Let's say myTextField.text = "test"
let textFieldCharacters = myTextField.text?.characters
// word is a string from the ENABLE list of words
let wordCharacters = word.characters
Then I dump the characters into an Array:
var wordCharactersArray = [Character]()
for character in wordCharacters {
wordCharacterArray.append(character)
}
var textFieldCharactersArray = [Character]()
for character in textFieldCharacters {
wordCharacterArray.append(character)
}
Then I create a Set from the character arrays:
let textFieldSet = Set<Character>(textFieldCharactersArray)
let wordSet = Set<Character>(wordCharactersArray)
Finally, I test to see if the textFieldSet is a superSet of wordSet with the following:
textFieldSet.isSuperset(of: wordSet)
Going back to my example, if myTextField.text is "test", I'm returning values for word whose characters are a superset of the wordSet, but the counts of the individual elements don't match the character counts of myTextField.text
In researching my issue, I've found CountedSet (fka NSCountedSet), which I think would resolve my issue. It has two method signatures:
public convenience init(array: [AnyObject])
public convenience init(set: Set<NSObject>)
I've tried initializing the 2 sets of characters like so:
let textFieldSet = CountedSet(array: textFieldCharacterArray)
let wordSet = CountedSet(array: wordCharacterArray)
I get the following error for the sets
Cannot convert value of type '[Character]' to expected argument type
'[AnyObject]'.
So I tried initializing the set like this:
let textFieldSet = CountedSet(array: textFieldCharacterArray as! [AnyObject])
Which yields the following error:
'AnyObject' is not a subtype of 'Character'
I've also tried to initialize the CountedSet with a Set, per the method signature, but I get errors when I try to do that, too.
Any suggestions how to initialize a CountedSet would be greatly appreciated.
You are correct that if you need to compare not just the presents of elements but also their count, you should use CountedSet, which is a renaming of NSCountedSet for swift 3.0. The problem you are running into is CountedSet can only accept elements that are objects and Characters are not. As Eric D points out in their comment, the easies way to get around this is by mapping your [Character] to [String] which will bridge to [NSString].
You are not running into this problem using Set, because it is a native Swift collection type that initialize with elements of any type. This is why you can initialize a Set with [Character].
To see the difference:
let word = "helo"
let wordCharacters = Array(word.characters)
let wordSet = Set(wordCharacters)
let wordCharStrings = wordCharacters.map{String($0)}
let wordCountedSet = CountedSet(array: wordCharStrings)
let textField = "hello"
let textFieldCharacters = Array(textField.characters)
let textSet = Set(textFieldCharacters)
let textFieldCharStrings = textFieldCharacters.map{String($0)}
let textFieldCountedSet = CountedSet(array: textFieldCharStrings)
textFieldCountedSet.isSubset(of: wordCountedSet as! Set<NSObject>) // returns false, but if word had two or more l's it would return true
textSet.isSubset(of: wordSet) // returns true
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!
How can I make this:
var originalString = "http://name.domain.com/image.jpg"
becomes this:
originalString = "http://name.domain.com/image_new.jpg"
I could not find any document about the new Range<String.Index> in Swift.
This is not a problem in Obj-C, but without any reference about Range, it suddenly becomes so confusing.
Thanks.
Edit:
Well, thanks for these solutions. However, let me give you more details about this question.
After uploading an image to server, it responds back with a String link, like above, and the image name is a random string.
The server also generates different versions of uploaded image (like Flickr). In order to get these images, I have to append a suffix into image name, it looks like this:
originalString = "http://image.domain.com/randomName_large.jpg" or "http://image.domain.com/randomName_medium.jpg"
So that's why I need to insert a String into another String. My solution is find the first . by scan the link backwardly and append a suffix before it, but the new Range<String.Index> makes it confusing.
There are some nice and useful methods on NSString that you should be able to use:
let originalString: NSString = "http://name.domain.com/image.jpg"
let extension = originalString.pathExtension // "jpg"
let withoutExt = originalString.stringByDeletingPathExtension() // "http://name.domain.com/image"
let imageName = withoutExt.lastPathComponent // "image"
let withoutFilename = withoutExt.stringByDeletingLastPathComponent() // "http://name.domain.com/"
let newString = withoutFilename
.stringByAppendingPathComponent("\(imageName)_new")
.stringByAppendingPathExtension(extension)
I only typed this into the browser (it's untested) but it should give you an idea...
This can be done with String manipulation functions. But what if the string
is
var originalString = "http://images.domain.com/image.jpg"
? You probably do not want to replace the first or all occurrences of the string
"image" here.
A better tool for this purpose might be NSURLComponents, which lets you
modify all components of a URL separately:
var originalString = "http://name.domain.com/image.jpg"
let urlComps = NSURLComponents(string: originalString)!
urlComps.path = "/image_new.jpg"
originalString = urlComps.URL!.absoluteString!
println(originalString) // http://name.domain.com/image_new.jpg
Why not using string interpolation?
var imageName = "image_new"
originalString = "http://images.domain.com/\(imageName).jpg"
Can somebody give me an example of how to make inserting data into an F# record more flexible?
I often see examples using records like this:
type Employee = {mutable name:string; mutable id:string}
let data =
[{name = "Thomas";id = "000"};
{name = "Johny";id = "001"};
{name = "Lucky";id = "002"};
{name = "Don";id = "003"}
]
Can't we start with no data at all and insert the data into the record later?
(What I mean is without declaration of the value of the data like in the example, so for example: the program is running and asking us to insert the data)
Can we doing something like this with record?
If you're talking about specifying values of a record as they become available, then you need to make fields of the record option so that you can represent the fact that value is missing. I'll use immutable records, because this is more common in functional style:
type Employee = { Name:option<string>; ID:option<string> }
Now you can create a record with only ID and add name when the user enters it:
let empty = { Name = None; ID = Some 123 }
let name = // read name from user
let full = { empty with Name = name }
If you're talking about adding items to a list as they become available, then you have several options. The direct one is to write a recursive function that repeatedly reads record and builds a list:
let rec readData i records =
let name = // read name from user
if name <> "" then
// Create new record and add it to our list
let itm = { Name = name; ID = string i }
readData (i + 1) (itm::records)
else
// Return records that we collected so far in the right order
records |> List.rev
Alternatively, you can also use sequence expressions (see for example free Chapter 12 (PDF) of Real-World Functional Programming). If you user interaction involves waiting for events (e.g. mouse click), then you can still use this style, but you'd need to wrap everything in asynchronous workflow and use Async.AwaitEvent.
Are you saw you often saw an example like that?
I'd say that it is not very idiomatic in F# to use mutable records.
Immutability is a rather large subject
to explain in one answer here, but
briefly: immutability means that the
objects you create never change:
they stay the way they were at
creation. In the immutable world, when
you want to 'change' something, you
create a new one, and throw away the
old one.
Anyway, if I understand your question correctly, you are actually talking about mutating data, not the record. So, you could have:
let data = []
let data = {name = "Thomas";id = "000"} :: data
let data = {{name = "Johny";id = "001"} :: data
But in this case, you aren't really 'changing' data, you are just creating a new list each time and pointing data at it.