flutter sqlite query makes null column into null string

Question

In the sqlite table i have null columns. I made a query to get all data from specific column and map its data into List<Map<String, dynamic>>:

List<Map<String, dynamic>> maps = List();
final db = await database;
var result = await db.query('tools_table', where: 'LifeCycle <> 2');
result.forEach((val) {
  maps.add(val);
});

but null column converted into the "null" and when i want to deserialize list of map into object :

ToolsModel.fromJson(Map<String, dynamic> json) {
...
    if (json['triggerImagesUrl'] != null) {
      triggerImagesUrl = List<String>();
      var job = jsonDecode(json['triggerImagesUrl']);
      job.forEach((v) {
        triggerImagesUrl.add(v);
      });
    }

I got error because json['TriggerUrl'] is nut null, it is "null" and var job = jsonDecode(json['TriggerUrl']); job be a null and job.forEach cause e exception.

Why null column is converted to the "null" and how can i prevent of this action ?

Can you share the schema and the insertion query?

Sanjay Sharma
– Sanjay Sharma

2020-05-03 10:31:50 +00:00
Commented May 3, 2020 at 10:31 — Sanjay Sharma
– Sanjay Sharma, Commented May 3, 2020 at 10:31
paste.ubuntu.com/p/fM7X32PPKb @snj

Cyrus the Great
– Cyrus the Great

2020-05-03 10:54:30 +00:00
Commented May 3, 2020 at 10:54 — Cyrus the Great
– Cyrus the Great, Commented May 3, 2020 at 10:54
Is TriggerUrl changed to TriggerImagesUrl?

Sanjay Sharma
– Sanjay Sharma

2020-05-03 11:00:12 +00:00
Commented May 3, 2020 at 11:00 — Sanjay Sharma
– Sanjay Sharma, Commented May 3, 2020 at 11:00
yes i changed @snj

Cyrus the Great
– Cyrus the Great

2020-05-03 11:00:43 +00:00
Commented May 3, 2020 at 11:00 — Cyrus the Great
– Cyrus the Great, Commented May 3, 2020 at 11:00
please share JSON response too. It can also be the issue

Sanjay Sharma
– Sanjay Sharma

2020-05-03 11:00:48 +00:00
Commented May 3, 2020 at 11:00 — Sanjay Sharma
– Sanjay Sharma, Commented May 3, 2020 at 11:00

Sanjay Sharma · Accepted Answer · 2020-05-03 11:47:41Z

1

Try this in dart pad

import 'dart:convert';
void main() {
  List<String> urls = null;
  var d = jsonEncode(urls);
  print(d  is String);
  print(jsonDecode(d) is String);
}

You'll get following output

true
false

So jsonEncode(urls) returns null string if urls is null.
Change this

Map<String, Object> mapToCacheActivatedToolItem(LogData.Data item) {
    var newMap = {
      "TriggerImagesUrl": item.triggerImagesUrl == null ? null : jsonEncode(urls)
    };
    return newMap;
  }

edited May 3, 2020 at 11:47

answered May 3, 2020 at 10:59

Sanjay Sharma

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