iterate trough map<List<dataModel>> in Dart Flutter - flutter

Question

I have 2 datamodels. the userDataModel and the PostDataModel.
Users may have multiple posts
so I would like to have the following fetching structure:
Map<userDataModel,List<PostDataModel>> = data
Can I iterate through data using indexes? (user index and then posts indexes ?)
something like for(user, data in data){}
or something like data[0][0]
In the end, I would like to have a listView of all the posts, one user at the time
I also would like to know how to print the data since printing data only returns instances.

Answer 1

First, using the structure you provided, Map<userDataModel,List<PostDataModel>>, you have to have two nested loops. To be able to iterate through all of them you will need to have some code like the following:
void main() {
var data = Map<UserDataModel, List<PostDataModel>>();
data.forEach((user, posts) {
for (var post in posts) {
print(post.name);
print(user.id);
}
});
}
class UserDataModel {
int id;
}
class PostDataModel {
String name;
}
However, since, as you mentioned, your posts belong to users, I would put the PostDataModel inside the UserDataModel. Then, your data will eventually look a little different:
void main() {
var data = List<UserDataModel>();
data.add(UserDataModel(1, [PostDataModel("one"),PostDataModel("two")]));
data.add(UserDataModel(2, [PostDataModel("three"),PostDataModel("four")]));
for (var user in data) {
for (var post in user.posts) {
print(user);
print(post);
}
}
}
class UserDataModel {
int id;
UserDataModel(this.id, this.posts);
List<PostDataModel> posts;
#override
String toString() {
var result = "";
result += "Id: $id\n";
var count = 0;
for(var post in posts) {
result += "Post $count, $post";
}
return result;
}
}
class PostDataModel {
String name;
PostDataModel(this.name);
#override
String toString() {
return "Name: $name\n";
}
}
It depends on your backend structure but I would suggest the second way.
As an answer to the second part of your question, look at the method toString. If you override it, you can customize the way your class is displayed when, for example, you use print(userDataModel. I created those classes as for example, so customize them for your own classes.
In fact, with the last example, you can access your posts by data[0].posts[0] as you requested.

Answer 2

I guess you could do something like
var data = userDataModel.map((user) => postDataModel.map((post) { post.useriD == user.userId ? post : null}).toList()).toList();

Answer 3

One possible solution is to iterate over the Map and over the List in a nested forEach:
data.forEach((user, posts) {
print(user);
posts.forEach((post) {
print(post);
});
print('---'); // end of the user's posts
});