wait for Future in for loop - sql

Question

I'm having a future which is a result of an sql query, in it I'm looping over each returned row to add it to a list with a map to encode it to a json format later.
In this loop I'm executing another query depending on the result in each row of the outer query and add those rows again to a map.
Future<Results> mysqlAllTags = mysqlCon.query(query).then((results){
// Make new list as a part of the JsonObject
json.tags = new List();
// Loop throught the row of the result from Mysql data
return results.forEach((row){
// Create Map to put the word, value, rating and id into the JsonObject
Map data = new Map();
// Put the Mysql data into the Map
data["word"] = row.word.toString();
data["value"] = row.value.toString();
data["rating"] = row.rating.toString();
data["id_tag"] = row.id_tag.toString();
data["replacing"] = null;
// Add the Map to the userPages list
json.tags.add(data);
}).then((e){
for(var tag in json.tags){
//Map dataReplacing = getReplacing(userId, row.id_tag.toString());
String replacingTags = getReplacingSQL(tag['id_tag'].toString());
mysqlCon.query(replacingTags).then((result){
result.forEach((row1){
Map map = new Map();
map["word"] = row1.word.toString();
map["value"] = row1.value.toString();
map["id_tag"] = row1.id_replacing_tag.toString();
tag["replacing"] = map;
}).then((e){
print("then inner for called");
return null;
});
print("then inner for called");
return null;
});
}
print("outer for returned");
// Send the data in UTF8 to the client
result = Helpers.formatJsonAndEncodeUtf8('OK', session:_session, data: [json]);
return null;
}).catchError((error){
result = Helpers.formatJsonAndEncodeUtf8('ERROR 856284555 (Could not load tags)', session:_session);
});
}).catchError((error){
result = Helpers.formatJsonAndEncodeUtf8('ERROR 2346644555 (Could not load tags)', session:_session);
});
return Future.wait([mysqlAllTags]).then((e){
print("future returned");
return result;
});
The result looks like this:
outer for returned
=== TO CLIENT ===
{"status":[{"message":"OK","csrfToken":"99"}],"data":[{"tags":[{"word":"Melon","value":"11.0","rating":"1","id_tag":"37","replacing":null},........}]}
=================
future returned
then inner for called
then inner for called
then inner for called
then inner for called
then inner for called
then inner for called
then inner for called
then inner for called
How can I wait until all Futures in my for loop are finished?

Answer 1

I solved it by adding the result declaration in the Future.wait(futures).then() function. Thank you Günter Zöchbauer for your input.
Future<Results> mysqlAllTags = mysqlCon.query(query).then((results){
// Make new list as a part of the JsonObject
json.tags = new List();
// Loop throught the row of the result from Mysql data
return results.forEach((row){
// Create Map to put the word, value, rating and id into the JsonObject
Map data = new Map();
// Put the Mysql data into the Map
data["word"] = row.word.toString();
data["value"] = row.value.toString();
data["rating"] = row.rating.toString();
data["id_tag"] = row.id_tag.toString();
data["replacing"] = null;
// Add the Map to the userPages list
json.tags.add(data);
}).then((e){
var futures = []; // added
for(var tag in json.tags){
print("row ");
print(json.tags);
//Map dataReplacing = getReplacing(userId, row.id_tag.toString());
String replacingTags = getReplacingSQL(tag['id_tag'].toString());
// added `futures.add(...)`
futures.add(mysqlCon.query(replacingTags).then((result) {
result.forEach((row1){
Map map = new Map();
map["word"] = row1.word.toString();
map["value"] = row1.value.toString();
map["id_tag"] = row1.id_replacing_tag.toString();
tag["replacing"] = map;
}).then((e){
print("then inner for called");
return null;
});
print("then inner for called");
return null;
}));
}
print("outer for returned");
// Send the data in UTF8 to the client
return Future.wait(futures).then((e){
result = Helpers.formatJsonAndEncodeUtf8('OK', session:_session, data: [json]);
}); // added
}).catchError((error){
result = Helpers.formatJsonAndEncodeUtf8('ERROR 856284555 (Could not load tags)', session:_session);
});
}).catchError((error){
result = Helpers.formatJsonAndEncodeUtf8('ERROR 2346644555 (Could not load tags)', session:_session);
});
return Future.wait([mysqlAllTags]).then((e){
print("future returned");
return result;
});

Answer 2

I'm not sure if this fixes all issues, it's not easy to see in such code what exactly returns a future. (I added comments where I added something)
Future<Results> mysqlAllTags = mysqlCon.query(query).then((results){
// Make new list as a part of the JsonObject
json.tags = new List();
// Loop throught the row of the result from Mysql data
return results.forEach((row){
// Create Map to put the word, value, rating and id into the JsonObject
Map data = new Map();
// Put the Mysql data into the Map
data["word"] = row.word.toString();
data["value"] = row.value.toString();
data["rating"] = row.rating.toString();
data["id_tag"] = row.id_tag.toString();
data["replacing"] = null;
// Add the Map to the userPages list
json.tags.add(data);
}).then((e){
var futures = []; // added
for(var tag in json.tags){
print("row ");
print(json.tags);
//Map dataReplacing = getReplacing(userId, row.id_tag.toString());
String replacingTags = getReplacingSQL(tag['id_tag'].toString());
// added `futures.add(...)`
futures.add(mysqlCon.query(replacingTags).then((result) {
result.forEach((row1){
Map map = new Map();
map["word"] = row1.word.toString();
map["value"] = row1.value.toString();
map["id_tag"] = row1.id_replacing_tag.toString();
tag["replacing"] = map;
}).then((e){
print("then inner for called");
return null;
});
print("then inner for called");
return null;
}));
}
print("outer for returned");
// Send the data in UTF8 to the client
result = Helpers.formatJsonAndEncodeUtf8('OK', session:_session, data: [json]);
return Future.wait(futures); // added
}).catchError((error){
result = Helpers.formatJsonAndEncodeUtf8('ERROR 856284555 (Could not load tags)', session:_session);
});
}).catchError((error){
result = Helpers.formatJsonAndEncodeUtf8('ERROR 2346644555 (Could not load tags)', session:_session);
});
return Future.wait([mysqlAllTags]).then((e){
print("future returned");
return result;
});