retrieve specific data from PraseQuery flutter - flutter

Question

I'm using back4app.com services (Prase SDK) on my flutter project to handle my backend.
in this method I try to query on specific object :
Future<List> getList(String date) async {
final QueryBuilder<ParseObject> parseQuery =
QueryBuilder<ParseObject>(ParseObject('UsersEaten'));
parseQuery
..whereContains('eatenBy', getUsrName!)
..whereEqualTo('eatenDate', date);
final ParseResponse apiResponse = await parseQuery.query();
if (apiResponse.success && apiResponse.results != null) {
List<dynamic>? apiRes = apiResponse.results;
and I've got whole data about this object as a List of Map :
[{"className":"UsersEaten","objectId":"OmrLz358Cb","createdAt":"2021-09-12T11:27:41.824Z","updatedAt":"2021-09-12T11:27:41.824Z","eatenTitle":"egg roll","eatenCal":180,"eatenFat":40,"eatenProtein":30,"eatenCarb":10,"eatenBy":"usr45","eatenDate":"2021-09-12"}, {"className":"UsersEaten","objectId":"lWIeMw54mH","createdAt":"2021-09-12T12:37:21.389Z","updatedAt":"2021-09-12T12:37:21.389Z","eatenTitle":"meat butter","eatenCal":235,"eatenFat":34,"eatenProtein":34,"eatenCarb":9,"eatenBy":"usr45","eatenDate":"2021-09-12"}]
but I dont need whole data I just want a specific Key , Values from this map for example I just need UsersEaten key values, how should I apply this kind of filter in my query???

Answer 1

In case I understand your question right, you want to reduce the amount of keys returned by the server.
This can be achieved using keysToReturn(List<String> keys).
/// Define which keys in an object to return.
///
/// [String] keys will only return the columns of a result you want the data for,
/// this is useful for large objects
void keysToReturn(List<String> keys) {
limiters['keys'] = concatenateArray(keys);
}
So your query might look something like this:
parseQuery
..whereContains('eatenBy', getUsrName!)
..whereEqualTo('eatenDate', date)
keysToReturn(['YOUR_KEY_THAT_SHOULD_BE_RETURNED']);
There is also the exact opposite of this method available, called excludeKeys(List<String> keys).

Answer 2

Create data class I chose the name Example for it
class Example {
String? className;
String? objectId;
String? createdAt;
String? updatedAt;
String? eatenTitle;
int? eatenCal;
int? eatenFat;
int? eatenProtein;
int? eatenCarb;
String? eatenBy;
String? eatenDate;
Example({
this.className,
this.objectId,
this.createdAt,
this.updatedAt,
this.eatenTitle,
this.eatenCal,
this.eatenFat,
this.eatenProtein,
this.eatenCarb,
this.eatenBy,
this.eatenDate,
});
Map<String, dynamic> toMap() {
return {
'className': className,
'objectId': objectId,
'createdAt': createdAt,
'updatedAt': updatedAt,
'eatenTitle': eatenTitle,
'eatenCal': eatenCal,
'eatenFat': eatenFat,
'eatenProtein': eatenProtein,
'eatenCarb': eatenCarb,
'eatenBy': eatenBy,
'eatenDate': eatenDate,
};
}
factory Example.fromMap(Map<String, dynamic> map) {
return Example(
className: map['className'],
objectId: map['objectId'],
createdAt: map['createdAt'],
updatedAt: map['updatedAt'],
eatenTitle: map['eatenTitle'],
eatenCal: map['eatenCal'],
eatenFat: map['eatenFat'],
eatenProtein: map['eatenProtein'],
eatenCarb: map['eatenCarb'],
eatenBy: map['eatenBy'],
eatenDate: map['eatenDate'],
);
}
String toJson() => json.encode(toMap());
factory Example.fromJson(String source) => Example.fromMap(json.decode(source));
}
Unfortunately, I don't know how to use this service back4app.com, but it should look like this
if (apiResponse.success && apiResponse.results != null) {
final maps = jsonDecode(apiResponse.results).cast<Map<String, dynamic>>();
var exampleList = List.generate(maps.length, (i) {
return Example.fromMap(maps[i]);
});
//sum of calories
num sum = 0;
exampleList.forEach((element){sum += element.eatenCal;});
print(sum);
}