Fetching data from Azure Cosmos DB in Flutter? - azure

Question

I wrote a function to fetch data using query from Azure Cosmos Database in Flutter/Dart, however it's giving error :
response.body: {"code":"BadRequest","message":"Message: {\"Errors\":[\"The input content is invalid because the required properties - 'æ©; ' - are missing\"]}\r\nActivityId: f75a0c6e-2c8d-4f13-a020-6e3c13fa5458, Request URI: /apps/f4533d11-81e3-4512-b639-0f0475c10611/services/401c9130-a85e-46a6-8311-c2dc8e5070d6/partitions/b5d2a58d-1304-414b-92c7-10e7fa95f679/replicas/131768862196689298p, RequestStats: , SDK: Microsoft.Azure.Documents.Common/2.0.0.0"}
I/flutter ( 5284): response.status: 400
Here is my piece of code
final response = await http.post(
endpointResource,
// Query
body: query,
// Post new message
headers: {
HttpHeaders.AUTHORIZATION: authToken,
HttpHeaders.CONTENT_TYPE: "application/query+json",
//'content-type': 'application/json',
'Accept': 'application/json',
//c.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
'x-ms-version': '2017-02-22',
'x-ms-date': date,
'x-ms-documentdb-isquery': 'true',
'x-ms-query-enable-crosspartition': 'true',
'x-ms-documentdb-query-enable-scan': 'true',
},
);
What should I do to get data back?

Answer 1

I managed to translate a code snippet from a working example in Javascript to Dart.
import 'dart:io';
import 'dart:convert';
import 'dart:async';
import 'dart:core';
import 'package:crypto/crypto.dart';
import 'package:hex/hex.dart';
class Cosmos{
String documentDBMasterKey;
Cosmos({this.documentDBMasterKey});
Future queryCosmos({url, method, body}) async{
String auth;
String documentDBMasterKey = this.documentDBMasterKey;
print("mastKey: $documentDBMasterKey");
method = method.trim(); //GET, POST, PUT or DEL
url = url.trim();
String utcString = HttpDate.format(DateTime.now());
print('RFC1123time: $utcString');
print('request url = ' + url);
String strippedurl =
url.replaceAllMapped(RegExp(r'^https?://[^/]+/'), (match) {
return '/';
});
print('stripped Url: $strippedurl');
List strippedparts = strippedurl.split('/');
int truestrippedcount = strippedparts.length - 1;
print('$truestrippedcount');
String resourceId;
String resType;
if (truestrippedcount % 2 != 0){
print('odd');
resType = strippedparts[truestrippedcount];
print('$resType');
if (truestrippedcount > 1){
int lastPart = strippedurl.lastIndexOf('/');
resourceId = strippedurl.substring(1, lastPart);
print('ResourceId: ' + resourceId);
}
}
else{
print('even');
resType = strippedparts[truestrippedcount -1];
print('resType: $resType');
strippedurl = strippedurl.substring(1);
print('strippedurl $strippedurl');
resourceId = strippedurl;
print('ResourceId: ' + resourceId);
}
String verb = method.toLowerCase();
String date = utcString.toLowerCase();
Base64Codec base64 = const Base64Codec();
var key = base64.decode(documentDBMasterKey); //Base64Bits --> BITS
print('key = ${HEX.encode(key)}');
print('masterKey = $documentDBMasterKey');
String text = (verb ?? '').toLowerCase() + '\n' +
(resType ?? '').toLowerCase() + '\n' +
(resourceId ?? '') + '\n' +
(date ?? '').toLowerCase() + '\n' +
'' + '\n';
print('text: $text');
var hmacSha256 = Hmac(sha256, key);
List<int> utf8Text = utf8.encode(text);
var hashSignature = hmacSha256.convert(utf8Text);
String base64Bits = base64.encode(hashSignature.bytes);
//Format our authentication token and URI encode it.
var masterToken = "master";
var tokenVersion = "1.0";
auth = Uri.encodeComponent('type=' + masterToken + '&ver=' + tokenVersion + '&sig=' + base64Bits);
print('auth= $auth');
Map<String, String> headers = {
'Accept': 'application/json',
'x-ms-version': '2016-07-11',
'Authorization': auth,
'x-ms-date': utcString,
'x-ms-documentdb-isquery' : 'true',
'Content-Type' : 'application/query+json',
'x-ms-documentdb-query-enablecrosspartition' : 'true',
};
Future<String> readResponse(HttpClientResponse response) {
final completer = Completer<String>();
final contents = StringBuffer();
response.transform(utf8.decoder).listen((data) {
contents.write(data);
}, onDone: () => completer.complete(contents.toString()));
return completer.future;
}
HttpClientRequest request;
HttpClient httpClient = new HttpClient();
if (method=='GET'){
request = await httpClient.getUrl(Uri.parse(url));
}
else if(method=='POST'){
request = await httpClient.postUrl(Uri.parse(url));
}
else if(method=='PUT'){
request = await httpClient.putUrl(Uri.parse(url));
}
else if(method=='DEL'){
request = await httpClient.deleteUrl(Uri.parse(url));
}
headers.forEach((key, value) {
request.headers.set(key,value);
});
if(body != null) {
request.add(utf8.encode(json.encode(body)));
}
HttpClientResponse aresponse = await request.close();
httpClient.close();
String aresponseString = await readResponse(aresponse);
return jsonDecode(aresponseString);
}
}
Just instantiate the class with your Cosmos Master Key:
Cosmos cosmos = Cosmos( documentDBMasterKey:'{your_cosmos_db_master_key}');
Query Cosmos Db by calling queryCosmos method. Pass 'url', 'method' and an optional 'body' as parameters:
// GET Example
() async {
Map<String, dynamic> get_dbs = await cosmos.queryCosmos(
url: 'https://{your_base_url}.documents.azure.com:443/dbs', method: 'GET');
print(get_dbs);
}
// POST Example (Query)
() async {
final Map<String, dynamic> body = {
"query":
"SELECT * FROM Faults f WHERE f.FaultId = #faultId",
"parameters": [
{"name": "#faultId", "value": 306000}
]
};
Map<String, dynamic> get_fault = await cosmos.queryCosmos(
url:
'https://{your_base_url}.documents.azure.com:443/dbs/{your_db}/colls/{your_collection}/docs',
method: 'POST',
body: body);
print('Get fault $get_fault');
}
Original code (JavaScript - Download to Postman and check pre-req script): https://github.com/MicrosoftCSA/documentdb-postman-collection
My code (dart): https://github.com/fvarela/cosmos_db_dart

Answer 2

I've created a Dart library to fetch data from a CosmosDB. For example to fetch documents from a collection you can just call this function:
import 'package:cosmosdb/cosmosdb.dart';
void main() {
final cosmosDB = CosmosDB(
masterKey: '<YOUR_MASTER_KEY>',
baseUrl: '<YOUR_BASE_URL>',
);
// get all documents from a collection
final documents = cosmosDB.documents.list('<YOUR_DATABASE>', '<YOUR_COLLECTION>');
print(documents);
}
GitHub: https://github.com/jonasfranz/cosmosdb
Package: https://pub.dev/packages/cosmosdb