toJson() invalid when recursively encode tree data structure - dart

Question

I have a Dart class that I am using as a node class for a tree data structure.
My goal here is to encode objects of this class and its child nodes recursively.
I have a toJson() method that takes the child Nodes List and calls jsonencode on them.
class Node{
String name;
Map<String, String> attributes;
List<Node> children = List<Node>();
Node(this.name, attributes) {
this.attributes = attributes;
this.children = List<Node>();
}
Node.fromJson(Map<dynamic,dynamic> _map) {
this.name = _map['name'];
this.children = new List<Node>();
this.attributes = _map['attributes'][0];
for(var i = 0; i < _map['children'].length;i++){
Node temp = new Node.fromJson(_map['children'][i]);
this.addChild(temp);
}
}
Map<String, dynamic> toJson() => {
'name': name,
'attributes': [attributes],
'children': [
...this.children.map(jsonEncode)
]
};
}
I have a unit test i created to test this functionality:
Node nodeMap = {
"name": "Name",
"attributes": [
{"#htag1": "tagval1"}
],
"children": [
{
"name": "NameChild1",
"attributes": [
{"#htag2": "tagval2"}
],
"children": []
},
{
"name": "NameChild2",
"attributes": [
{"#htag3": "tagval3"}
],
"children": []
}
]
};
UNode unodeInst = new UNode.fromJson(nodeMap);
// Act
var nodeCreate = nodeInst.toJson();
// Assert
expect(nodeCreate, equals(nodeMap));
Here is the output of my unit test
Expected: {
'name': 'Name',
'attributes': [{'#htag1': 'tagval1'}],
'children': [
{
'name': 'NameChild1',
'attributes': [{'#htag2': 'tagval2'}],
'children': []
},
{
'name': 'NameChild2',
'attributes': [{'#htag3': 'tagval3'}],
'children': []
}
]
}
Actual: {
'name': 'Name',
'attributes': [{'#htag1': 'tagval1'}],
'children': [
'{"name":"NameChild1","attributes":[{"#htag2":"tagval2"}],"children":[]}',
'{"name":"NameChild2","attributes":[{"#htag3":"tagval3"}],"children":[]}'
]
}
Which: at location ['children'][0] is '{"name":"NameChild1","attributes":[{"#htag2":"tagval2"}],"children":[]}' which expected a map
As you see its not encoding my object correctly.
I believe this is happening because when i reclusively call jsonencode this method returns a string that is placed into the children array.
I believe part of my problem is that i dont fully understand the d diffrence between jsonencode() and toJson().
It is my understanding that jsonencode() calls toJson().. but jsonencode() returns a string and toJson() returns a Map<String, dynamic>.. so i think what i want here is to call toJson() recursively and not jsonencode.
Does this sound correct?
But i cannot figure out how to do this on a list in this situation.
I have tried the following
...this.children.map(this.toJson())
but i get "The argument type 'Map<String, dynamic>' can't be assigned to the parameter type 'dynamic Function(Node)'"
...this.children.forEach((element) {element.toJson()})
but i get "Spread elements in list or set literals must implement 'Iterable'"
Does this mean i have to implement the Iterable interface in my class?

Answer 1

You're just using the map method incorrectly. Use the following instead.
[
...this.children.map((e) => e.toJson())
]
It's also unnecessary to use spread with a literal list or use this. You can simplify the code to just
children.map((e) => e.toJson()).toList()