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如何使用Dart/FLIFT在CloudFireStore中存储简单矩阵?

google-cloud-firestore dart flutter

ThiagoAM · 技术社区 · 6 年前

假设在Dart中有以下整数矩阵:

final List<List<int>> myMatrix = [
  [1, 0, 0],
  [0, 1, 0],
  [0, 0, 1],
];

然后我尝试将其存储在Cloud Firestore中,如下所示:

await Firestore.instance.collection("anyCollection").add({
    "matrix" : myMatrix,
});

但是,当我运行上面的代码时,模拟器崩溃,我得到以下错误:

*** First throw call stack:
(
    0   CoreFoundation                      0x00007fff23c4f02e __exceptionPreprocess + 350
    1   libobjc.A.dylib                     0x00007fff50b97b20 objc_exception_throw + 48
    2   Runner                              0x000000010e83f8b5 _ZN8firebase9firestore4util16ObjcThrowHandlerENS1_13ExceptionTypeEPKcS4_iRKNSt3__112basic_stringIcNS5_11char_traitsIcEENS5_9allocatorIcEEEE + 581
    3   Runner                              0x000000010e83edf3 _ZN8firebase9firestore4util5ThrowENS1_13ExceptionTypeEPKcS4_iRKNSt3__112basic_stringIcNS5_11char_traitsIcEENS5_9allocatorIcEEEE + 67
    4   Runner                              0x000000010e890589 _ZN8firebase9firestore4util20ThrowInvalidArgumentIJEEEvPKcDpRKT_ + 57
    5   Runner                              0x000000010e959f65 -[FSTUserDataConverter parseData:context:] + 1045
    6   Runner                              0x000000010e<â¦>
Lost connection to device.

我在跑步 cloud_firestore: ^0.13.0+1 pubspec.yaml 文件运行时一切正常 flutter doctor 指挥也是如此。

0 回复 | 直到 6 年前

rsalinas 6 年前

而您可以在Firestore中存储一个数组,如 documentation ,不允许在其中存储另一个数组。

您可以采取一种方法,将数组作为字段存储在文档中,这样实际上就可以将每个数组分开。这是显示在这里 thread 或 this one .

halfer Jatin Pandey 6 年前

以下方法适用于您作为示例给出的矩阵,但您无法直接从Firestore查询矩阵。您必须取出整个矩阵,解析它,然后使用它:

final List<List<int>> myMatrix = [
  [1, 0, 0],
  [0, 1, 0],
  [0, 0, 1],
];

// Encode your matrix into a JSON String to add to Firestore
String jsonMatrix = jsonEncode(myMatrix);

// Decode your Json String into a JSON object
var decodedMatrix = jsonDecode(jsonMatrix);

// Decode JSON object back into your matrix
List<List<int>> newList = List<List<int>>.from(decodedMatrix.map((row){
  return List<int>.from(row.map((value) => int.parse(value.toString())));
}));

// Print to show that the new object is of the same type as the original Matrix
print(newList is List<List<int>>);

ThiagoAM 6 年前

我最终制作了以下帮助程序,将矩阵转换为与Firestore兼容的映射:

class MatrixHelper {

  // Creates a map that can be stored in Firebase from an int matrix.
  static Map<String, dynamic> mapFromIntMatrix(List<List<int>> intMatrix) {
    Map<String, Map<String, dynamic>> map = {};
    int index = 0;
    for (List<int> row in intMatrix) {
      map.addEntries([MapEntry(index.toString(), {})]);
      for (int value in row) {
        map[index.toString()].addEntries(
            [MapEntry(value.toString(), true)]
        );
      }
      index += 1;
    }
    return map;
  }

  // Creates an int matrix from a dynamic map.
  static List<List<int>> intMatrixFromMap(Map<dynamic, dynamic> dynamicMap) {
    final map = Map<String, dynamic>.from(dynamicMap);
    List<List<int>> matrix = [];
    map.forEach((stringIndex, value) {
      Map<String, dynamic> rowMap = Map<String, dynamic>.from(value);
      List<int> row = [];
      rowMap.forEach((stringNumber, boolean) {
        row.add(int.parse(stringNumber));
      });
      matrix.add(row);
    });
    return matrix;
  }

}

它的使用非常简单,要在Firestore中保存,它是这样的:

final List<List<int>> myMatrix = [
  [1, 0, 0],
  [0, 1, 0],
  [0, 0, 1],
];

await Firestore.instance.collection("anyCollection").add({
    "matrix" : MatrixHelper.mapFromIntMatrix(myMatrix),
});

要从Firestore加载矩阵,如下所示:

// Loads the DocumentSnapshot:
final document = await Firestore.instance.collection("anyCollection").document("anyDocument").get();
// Retrieves the Matrix:
final List<List<int>> matrix = MatrixHelper.intMatrixFromMap(document.data["matrix"]);