Flutter：制作模型以将json保存到sqlite并将数据作为对象返回

Question

我有这个json：

{
"ProductCoreId":0,
"LifeCycle":1,
"OwnerPartyRoleId":0,
"TriggerImages":null,
"TriggerImagesUrl":[
"/Files/Images/Channels/sdp.png"
],
"TriggerChannelIds":[
1287
],
"ActionImages":null,
"ActionImagesUrl":[]
}

您可以看到，我有2个列表TriggerImagesUrl和TriggerChannelIds。现在，我想将此json模型保存到sqlite中，因此我根据json制作了该类模型以保存到数据库中：

class ToolsByChannelIdDbModel {
  int productCoreId;
  int lifeCycle;
  int ownerPartyRoleId;
  Null triggerImages;
  String triggerImagesUrl;
  String triggerChannelIds;

      ToolsByChannelIdDbModel(
          {this.productCoreId,
          this.lifeCycle,
          this.ownerPartyRoleId,
          this.triggerImages,
          this.triggerImagesUrl,
          this.triggerChannelIds});

      ToolsByChannelIdDbModel.fromJson(Map<String, dynamic> json) {
        productCoreId = json['ProductCoreId'];
        lifeCycle = json['LifeCycle'];
        ownerPartyRoleId = json['OwnerPartyRoleId'];
        triggerImages = json['TriggerImages'];
        triggerImagesUrl = json['TriggerImagesUrl'];
        triggerChannelIds = json['TriggerChannelIds'];
      }

      Map<String, dynamic> toJson() {
        final Map<String, dynamic> data = new Map<String, dynamic>();
        data['ProductCoreId'] = this.productCoreId;
        data['LifeCycle'] = this.lifeCycle;
        data['OwnerPartyRoleId'] = this.ownerPartyRoleId;
        data['TriggerImages'] = this.triggerImages;
        data['TriggerImagesUrl'] = this.triggerImagesUrl;
        data['TriggerChannelIds'] = this.triggerChannelIds;
        return data;
      }
    }

由于您现在sqlite不接受列表作为类型，所以我将列表作为json字符串制成，所以我这样保存：

 ToolsByChannelIdDbModel model = ToolsByChannelIdDbModel();
 model.productCoreId = item.productCoreId;
 model.lifeCycle = item.lifeCycle;
 model.ownerPartyRoleId = item.ownerPartyRoleId;
 model.triggerImagesUrl = jsonEncode(item.triggerImagesUrl);
 model.triggerChannelIds = jsonEncode(item.triggerChannelIds);
 db.insert("tools_table", model.toJson());

item.triggerImagesUrl和item.triggerChannelIds是一个列表，我将它们映射到json字符串中以保存到数据库中。到目前为止，一切都很好，并且这些列表已保存到数据库中。当我进行查询并且想要将db.rawQuery的结果解码为我的对象时，就会发生问题。

  Future<List<ToolsByChannelIdDbModel>> getTools(
      int channelId) async {
    List<ToolsByChannelIdDbModel> list = 
    try {
      var result = await DBProvider.db.getToolsById(channelId);
      result.forEach((item) {
        list.add(ToolsByChannelIdDbModel.fromJson(item));
      });
    } catch (e) {
      print(e);
    }
    return list;
  }
}

[await DBProvider.db.getToolsById(channelId);部分工作正常，返回了数据映射，triggerImagesUrl和triggerChannelIds是json字符串，但是当我想通过此部分中的ToolsByChannelIdDbModel.fromJson(item)将映射转换为对象时：

String triggerImagesUrl;字符串triggerChannelIds;

在模型中，我出错了，因为我将这些字段声明为String，但它们是列表。

如何将这些列表存储到数据库中以及如何将它们映射到对象中？

Answer 1

尝试一下：

class ToolsByChannelIdDbModel {
    int productCoreId;
    int lifeCycle;
    int ownerPartyRoleId;
    dynamic triggerImages;
    List<String> triggerImagesUrl;
    List<int> triggerChannelIds;
    dynamic actionImages;
    List<dynamic> actionImagesUrl;

   /* Create instance without ID (database will auto generate one if you specified an 
   id column)*/       

   ToolsByChannelIdDbModel({
    this.lifeCycle,
    this.ownerPartyRoleId,
    this.triggerImages,
    this.triggerImagesUrl,
    this.triggerChannelIds,
    this.actionImages,
    this.actionImagesUrl,
  });

  // Create instance with ID  

  ToolsByChannelIdDbModel.withId({
    this.productCoreId,
    this.lifeCycle,
    this.ownerPartyRoleId,
    this.triggerImages,
    this.triggerImagesUrl,
    this.triggerChannelIds,
    this.actionImages,
    this.actionImagesUrl,
  });

  /* When you want to add object to database you can use .toMap() this will 
    convert ToolsByChannelIdDbModel instance to a Map*/  

  Map<String, dynamic> toMap()
  {
      var tempMap = Map<String, dynamic>();
      if(productCoreId != null)
      { 
          tempMap['productCoreId'] = productCoreId; 
      }
      tempMap['lifeCycle'] = lifeCycle;
      tempMap['ownerPartyRoleId'] = ownerPartyRoleId;
      tempMap['triggerImages'] = triggerImages;
      tempMap['triggerImagesUrl'] = List<dynamic>.from(triggerImagesUrl.map((x) => 
      x));
      tempMap['triggerChannelIds'] = List<dynamic>.from(triggerChannelIds.map((x) => 
      x));
      tempMap['actionImages'] = actionImages;
      tempMap['actionImagesUrl'] = List<dynamic>.from(actionImagesUrl.map((x) => 
      x));

      return tempMap;
  }

  /* Named constructor to create ToolsByChannelIdDbModel instance from a Map that you 
  get from database */     

  ToolsByChannelIdDbModel.fromMap(Map<String, dynamic> map)
  {
      this.productCoreId = map['productCoreId'];
      this.lifeCycle = map['lifeCycle'];
      this.ownerPartyRoleId = map['ownerPartyRoleId'];
      this.triggerImages = map['triggerImages'];
      this.triggerImagesUrl = List<String>.from(map['triggerImagesUrl'].map((x) => 
      x));
      this.triggerChannelIds = List<int>.from(map['triggerChannelIds'].map((x) => 
      x));
      this.actionImages = map['actionImages'];
      this.actionImagesUrl = List<dynamic>.from(map['actionImagesUrl'].map((x) => 
      x));
  }
}

希望这有所帮助！