Appending to Array in Deeply Nested Dictionary of Arrays - arrays

Question

I am having the following problem in Swift. First, I declare a data structure, like this:
var books = [String : Dictionary<String, Dictionary<String, Dictionary<String, Array<Dictionary<String, String>>>>>]()
I later initialize the var like this:
books = [
"Fiction" : [
"Genre Fiction" : [
"Mystery" : [
"Classics" : [
["Title" : "Ten Little Indians",
"Author" : "Agatha Christie",
"read" : "no"],
["Title" : "A Study in Scarlet",
"Author" : "Arthur Conan Doyle",
"read" : "no"],
]
]
]
]
]
Note that the compiler does not complain about it. Later, I create a new dictionary which I would like to append to that innermost array, like this:
var bookDict = Dictionary<String, String>()
bookDict = ["title" : dict.valueForKey("title") as! String,
"author": dict.valueForKey("author") as! String,
"read" : dict.valueForKey("read") as! String ]
books["category"]["genre"]["focus"]["set"].append(bookDict)
However, I get a compiler error that "Cannot invoke append with an argument list of type (Dictionary < String, String>)". This is confusing to me because the books data structure is declared such that that innermost array is an array of Dictionary< String, String>.
What am I missing?

Answer 1

It's not clear during compile time if the key is really present in the dictionary so dictionaries always return optional values. You have to check this optionals:
if let category = books["Fiction"] {
if let genre = category["Genre Fiction"] {
if let focus = genre["Mystery"] {
if var set = focus["Classics"] {
set.append(bookDict)
}
}
}
}
Or you can do it also like this:
books["Fiction"]?["Genre Fiction"]?["Mystery"]?["Classics"]?.append(bookDict)