Retrieve child by auto id value in firebase (TableView) - ios

Question

I have a UI table view and when I swipe the cell I delete the cell, but not the value in firebase. I have searched everywhere but cannot find it. How can I delete the array I swiped on from the cell in my firebase. Below is how I set up my firebase database. The array I'm trying to delete is the corresponding one in the cell e.g. it may be "-L4BMZBIcYMp_f2LDMbp" etc.
Also the code I have to delete the cell and where I would find the array corresponding to the cell
func tableView(_ tableView: UITableView, commit editingStyle: UITableViewCellEditingStyle, forRowAt indexPath: IndexPath) {
let fliper = self.flipList[indexPath.row]
if let itemID = fliper.item{
FIRDatabase.database().reference().child("Flip").child("..I need to find out how to get child auto id").removeValue(completionBlock: { (error, ref) in
if error != nil {
print("Failed! to delete message")
return
}
//one way of updating the table
self.flipList.remove(at: indexPath.row)
self.tableViewFlips.deleteRows(at: [indexPath], with: .automatic)
})
}`

Answer 1

The "key" here is to ensure that when the data is initially loaded from Firebase you keep the node key intact. So for example. say you have a messaging app that has posts. Here's a class that would store the data from Firebase
struct PostStruct {
post_key = ""
post_text = ""
posted_by_uid = ""
}
and then those structs would be used to populate your dataSource array.
Given the above structure:
When your dataSource is initially populated from Firebase, as you read in each post node, create a post struct, populate it with data from Firebase and store it in a dataSource, typically an array.
When you swipe to delete there are about 100 options for handling the actual delete process but here are a couple:
1) Your tableView is backed by an array. If you swipe to delete row 2 (for example), inspect the object (struct) to be deleted, capture the post_key from the stuct, then delete the node from Firebase (since you know the node key) and then query the array for that object key, delete the row in the array and reload your tableView/update the UI.
2) When you swipe to delete a row, inspect the object and obtain the post_key. Then remove the object from Firebase. That would trigger a .childRemoved event (assuming you've attached the corresponding listener). When your app receives that event, determine which object it is (via key or other means) and remove it from the array and reload the tableView.
3) If you swipe to delete row 2, get the struct from row 2 in your dataSource array, read the key from that struct, remove row 2, remove the object from Firebase and reload the tableView.
There are many, many other way to tackle this; your dataSource array could store the actual snapshot data from firebase or it could store a series of key: value pairs with the key being the node key and the value being the data within that node (as a stuct, class, string etc).
Edit:
Some additional info to clarify the above.
Supposed we are using the structure above and firebase has matching nodes like this
root
posts
post_key_0 //created via childByAutoId
post_text: "some post text"
posted_by_uid: "uid_0"
post_key_1 //created via childByAutoId
post_text: "another post"
posted_by_uid: "uid_1"
then to read the posts and populate a dataSource array:
struct PostStruct {
post_key = ""
post_text = ""
posted_by_uid = ""
}
var dataSourceArray = [PostStruct]()
func button0() {
let itemsRef = self.ref.child("items")
itemsRef.observeSingleEvent(of: .value, with: { snapshot in
for child in snapshot.children {
let snap = child as! DataSnapshot
let dict = snap.value as! [String: Any]
let postKey = snap.key
let postText = dict["post_text"] as! String
let postedByUid = dict["posted_by_uid"] as! String
let post = PostStruct(post_key: postKey, post_text: postText, posted_by_uid: ppostedByUid)
self.dataSourceArray.append(post)
}
self.someTableView.reloadData()
})
}
from there it's pretty straightforward.
Assuming we are using option 3), when the user swipes to delete row 2 for example you get that post from the array, row 2
let post = self.dataSourceArray[2]
let postKey = post.post_key
now you know the firebase key so it can then be removed
let thisPostRef = fbRef.child("posts").child(postKey)
thisPostRef.remove()
and finally remove it from the array and refresh the tableView
self.dataSourceArray.remove(at: 2)
self.someTableView.reloadData()
The code would be different if you went with one of the other options but the concepts are similar and can be applied to each.