Question

我已经实现了将返回的JSON数据存储在本地数据库（SQFlite）中的代码。我只想存储is_deleted参数为0的那些数据。我不确定如何实施。任何解决方案都会有很大帮助。

这是JSON：

"subject": [
        {
            "univ_spec_sub_id": "53",
            "univ_year_sem_id": "18",
            "sem_id": "2",
            "university_id": "5",
            "master_course_id": "36",
            "subject_name": "Programming and Problem Solving",
            "subject_desc": "99",
            "info": "Programming and Problem Solving using Python",
            "no_units": "6",
            "is_deleted": "0",
            
        },
        {
            "univ_spec_sub_id": "59",
            "univ_year_sem_id": "18",
            "sem_id": "2",
            "university_id": "5",
            "master_course_id": "37",
            "subject_name": "Basic Electrical Engineering",
            "subject_desc": "99",
            "info": "",
            "no_units": "100",
            "is_deleted": "0",
            
        },
        {
            "univ_spec_sub_id": "61",
            "univ_year_sem_id": "18",
            "sem_id": "2",
            "university_id": "5",
            "master_course_id": "38",
            "subject_name": "Engineering Mathematics II",
            "subject_desc": "99",
            "info": "",
            "no_units": "6",
            "is_deleted": "0",
            
        },
        {
            "univ_spec_sub_id": "65",
            "univ_year_sem_id": "18",
            "sem_id": "2",
            "university_id": "5",
            "master_course_id": "39",
            "subject_name": "Engineering Graphics",
            "subject_desc": "99",
            "info": "",
            "no_units": "6",
            "is_deleted": "1",
        }
    ],

我已经实现了以下代码，以将返回的JSON存储到本地数据库中。

Future<Semdata> semdata(String url, {Map body} ) {
    return http.post(url,
          body:body).then((http.Response response){
      if (response.statusCode < 200 || response.statusCode > 400 || json == null) {
      throw new Exception("Error while fetching data");
    }
    //JsonDecoder().convert(response.body);
    var extractdata = json.decode(response.body);
    List subdata = extractdata["subject"];
    Map<String, dynamic> decodedData = json.decode(response.body);

    
    for(Map<String, dynamic> subjectMap in decodedData['subject']){
      print(subjectMap["subject"]["is_deleted"]);
      if(subjectMap["subject"]["is_deleted"]== "0"){
        db.savesubject(subjectMap);
      }
      // db.savesubject(subjectMap);
      
    }
    return Semdata.fromJson(json.decode(response.body));
    
    });
          
  }

Answer 1

（重写我的回答，因为我认为我全都错了，我想我对json.decode（response.body）的多个相同调用感到困惑。）

这里我假设您还没有启动数据库...

一种解决方案是创建一个包含所有主题字段的表。在这里，我假设univ_spec_sub_id是主键（唯一）。

var db =
    await openDatabase(path, version: 1, onCreate: (db, version) async {
  await db.execute('''
CREATE TABLE Subject (
    univ_spec_sub_id TEXT PRIMARY KEY,
    univ_year_sem_id TEXT,
    sem_id TEXT,
    university_id TEXT,
    master_course_id TEXT,
    subject_name TEXT,
    subject_desc TEXT,
    info TEXT,
    no_units TEXT,
    is_deleted TEXT);
  ''');
});

接收数据时，应对其进行解码，并保留带有'is_deleted'=='0'的项目，并在事务中将其添加到数据库中

// Decode the body
var responseData = jsonDecode(response.body) as Map;

// Only keep data with 'is_deleted' == '0' in a list
var subjects = (responseData['subject'] as List)
    .map((raw) => (raw as Map)?.cast<String, dynamic>())
    .where((map) => map['is_deleted'] == '0');

// Save subjects in a transaction
if (subjects.isNotEmpty) {
  await db.transaction((txn) async {
    for (var subjects in subjects) {
      await txn.insert('Subject', subjects);
    }
  });
}

将JSON保存在本地数据库中

1 个答案: