How to work with Firebase Asynchronously? Database reading giving odd results - swift

Question

I have written the following function to search through my Firebase database and I have also looked into using debug statements and tested with breakpoints to see this function is pulling the correct data and it is. But when I return the array at the end, the array is empty. As far as I understand this is due to the asynchronous nature of firebase. The function is getting to the end before the data is being added to the array. How do I fix this so it can work as intended, I want to return an array of items which I can then use for other functions.
static func SearchPostsByTags(tags: [String]) -> [Post]{
var result = [Post]()
let dbref = FIRDatabase.database().reference().child("posts")
dbref.observeSingleEvent(of: .value, with: { snap in
let comps = snap.value as! [String : AnyObject]
for(_, value) in comps {
let rawTags = value["tags"] as? NSArray
let compTags = rawTags as? [String]
if compTags != nil {
for cTag in compTags! {
for tag in tags {
if (tag == cTag) {
let foundPost = Post()
foundPost.postID = value["postID"] as! String
foundPost.title = value["title"] as! String
result.append(foundPost)
}
}
}
}
}
})
return result
}
}

Answer 1

You are returning your array before the async call ends. You should fill your array inside the async call and call then another method, which provides the results.
static func SearchPostsByTags(tags: [String]) {
let dbref = FIRDatabase.database().reference().child("posts")
dbref.observeSingleEvent(of: .value, with: { snap in
let comps = snap.value as! [String : AnyObject]
var result = [Post]()
for(_, value) in comps {
let rawTags = value["tags"] as? NSArray
let compTags = rawTags as? [String]
if compTags != nil {
for cTag in compTags! {
for tag in tags {
if (tag == cTag) {
let foundPost = Post()
foundPost.postID = value["postID"] as! String
foundPost.title = value["title"] as! String
result.append(foundPost)
}
}
}
}
}
// Call some func to deliver the finished result array
// You can also work with completion handlers - if you want to try have a look at callbacks / completion handler section of apples documentation
provideTheFinishedArr(result)
})
}