Deserializing a JSON value from an API - curly vs. square brackets - json

Question

I am working to integrate some weather info from an API where I get a return value like this ...
{"coord":{"lon":-85.6,"lat":43.05},"weather":[{"id":803,"main":"Clouds","description":"broken clouds","icon":"04d"}],"base":"stations","main":{"temp":277.33,"pressure":1010,"humidity":65,"temp_min":276.15,"temp_max":279.15},"visibility":16093,"wind":{"speed":5.7,"deg":100,"gust":8.2},"clouds":{"all":75},"dt":1524076680,"sys":{"type":1,"id":1410,"message":0.0043,"country":"US","sunrise":1524048860,"sunset":1524097768},"id":420018526,"name":"Grand Rapids","cod":200}
I have created a built_value and built_collection object to deserialize into. If I build the object "by hand" and serialize it, and JSON encode it ...
var w = new Welcome((b) => b
..id = 420018526
..name = "Grand Rapids"
..weather.add(new Weather((w)=>w
..id = 803
..main = "Clouds"
..description = "broken clouds"
..icon = "04d"
))
..cod = 200
..coord.lat = 43.05
..coord.lon= -85.6
..base = 'stations'
..main.temp = 277.33
..main.pressure = 1010
..main.humidity = 65
..main.temp_min = 276.15
..main.temp_max = 279.15
..visibility = 16093
..wind.speed = 5.7
..wind.deg = 100
..wind.gust = 8.2
..clouds.all = 75
..dt = 1524076680
..sys.type = 1
..sys.id = 1410
..sys.message = 0.0043
..sys.country = "US"
..sys.sunrise = 1524048860
..sys.sunset = 1524097768
);
var ws = serializers.serialize(w);
var wsj = JSON.encode(ws);
I get something like this ...
["Welcome","coord",["lon",-85.6,"lat",43.05],"weather",[["id",803,"main","Clouds","description","broken clouds","icon","04d"]],"base","stations","main",["temp",277.33,"pressure",1010,"humidity",65,"temp_min",276.15,"temp_max",279.15],"visibility",16093,"wind",["speed",5.7,"deg",100,"gust",8.2],"clouds",["all",75],"dt",1524076680,"sys",["type",1,"id",1410,"message",0.0043,"country","US","sunrise",1524048860,"sunset",1524097768],"id",420018526,"name","Grand Rapids","cod",200]
... which looks amazingly similar, but you'll notice that the dart:convert JSON libraries seem to prefer square brackets [ over curly ones {
When I try to deserialze the curly brackets wsjdA = JSON.decode(wJson); I get an error
type '_InternalLinkedHashMap<String, dynamic>' is not a subtype of type 'Welcome' of 'wsjdA' where
_InternalLinkedHashMap is from dart:collection
String is from dart:core
Welcome is from package:ex_models/src/weather.dart
But if I do this goofy thing (to parse out the square brackets for curly and add the first string "Welcome" ...
var wJsonB= '["Welcome",' + wJson
.replaceAll('{', '[')
.replaceAll('}', ']')
.replaceAll(':', ',')
.substring(1);
... it works fine
Am I missing something - is there an easier way to do the JSON/Object deserialization in dart. I'd really like to be able to parse a valid JSON API response into a dart object, in a standard way, without the manual parsing.
I think this may have worked if it weren't for the list of Weather objects within the Root/Welcome object. Because this object contains a list of objects, this is confusing things a bit? This is a BuiltList in my object.
I am already using a built_value object with built_collections and using the dart:convert libraries. Wondering if there is something I am missing?

Answer 1

[] is for lists/arrays, {} is for maps. With built_value you can use properties of type BuiltList and BuiltMap.
JSON.decode(wJson); doesn't return instances of classes, it just makes lists, maps, and separate primitive values out of a JSON string.
built_value has it's own serialization from what JSON.decode(...) returns to concrete instances of classes.
built_value by default has a reduced JSON format that won't be compatible with your JSON. For that you need to register the StandardJsonPlugin (see also https://github.com/google/built_value.dart/issues/171)
For details about serialization with built_value see https://medium.com/dartlang/darts-built-value-for-serialization-f5db9d0f4159.