Question: Possible to serialize & deserialize a field of type Map<String, dynamic> ?

[jimmyff]

Hey, I've attempted to create a class that will cache the output from an external API. I'd like the output from the api to be stored as a generic json: Map/BuilMap<String, dynamic> however the serializer complains about that. I know I could json encode the data and just store it as a string, but then i'd loose the nice perk that I can query the data field if it's stored in firestore as a Map/Object.

Is this kind of thing possible I do I need to break this in to two documents and handle them both individually?

//...
abstract class CachedFile implements Built<CachedFile, CachedFileBuilder> {
  static Serializer<CachedFile> get serializer => _$cachedFileSerializer;

  DateTime get created;
  DateTime get updated;

  BuiltMap<String, dynamic> get data;

//...

with serializer:

      ..addBuilderFactory(
          const FullType(BuiltMap, [FullType(String), FullType(dynamic)]),
          () => MapBuilder<String, dynamic>())

The above fails with Bad state: No serializer for '_Map<String, dynamic>'. when I try to serialize.

[jimmyff]

I think the issue is the data that I'm serializing, contains maps, lists etc. That's why I'm getting the _Map error. So I guess the question is there a way to make the dynamic part work, I'm guessing not

[ahmednfwela]

from my experience it works just fine, can you share your serializer configuration ?

[jimmyff]

Oh interesting - thanks @ahmednfwela -I had given up thinking it wasn't possible.

final Serializers serializers = (_$serializers.toBuilder()
      ..addPlugin(StandardJsonPlugin())
      ..addBuilderFactory(
          const FullType(BuiltMap, [FullType(String), FullType(dynamic)]),
          () => MapBuilder<String, dynamic>())
    )
    .build();

Could you possibly share how your class & seriazliers look to get it working?

[jimmyff]

Even just trying this fails for me:

      final json = <String, dynamic>{
        'name': 'foobar',
        'age': 99,
        'timestamp': {'value': true},
        'lists': [1, 2, 42],
      };

      final serialized = serializers.serialize(
          BuiltMap<String, dynamic>.from(json),
          specifiedType:
              const FullType(BuiltMap, [FullType(String), FullType(dynamic)]));

with Bad state: No serializer for '_Map<String, bool>'.

[ahmednfwela]

@jimmyff can you try using BuiltMap<String, JsonObject?> instead of dynamic ?

[jimmyff]

@jimmyff can you try using BuiltMap<String, JsonObject?> instead of dynamic ?

Ohh interesting, thanks! I've got this working:

    test('serializing and deserializing json maps', () {
      final json = <String, dynamic>{
        'name': 'foobar',
        'age': 99,
        'timestamp': {'value': true},
        'lists': [1, 2, 42],
      };

      final serialized = serializers.serialize(
          BuiltMap<String, JsonObject>.from(
              json.map((key, value) => MapEntry(key, JsonObject(value)))),
          specifiedType: const FullType(
              BuiltMap, [FullType(String), FullType(JsonObject)]));

      final deserialized = BuiltMap<String, JsonObject>(serializers.deserialize(
          serialized,
          specifiedType: const FullType(
              BuiltMap, [FullType(String), FullType(JsonObject)])));

      final unpacked =
          deserialized.map((key, value) => MapEntry(key, value.value)).asMap();

      expect(unpacked, equals(json));
    });

It's quite verbose with having to pack and unpack the maps with JsonObject's -is there a more elegant way of doing this?

I'll try to get this working on my class now. Thanks again

[jimmyff]

hmm, maybe the whole map should just be type JsonObject!

[ahmednfwela]

be careful you don't hit this bug if you have possible null values in your map #1242

the proper way in your example:

test('serializing and deserializing json maps', () {
  final json = <String, dynamic>{
    'name': 'foobar',
    'age': 99,
    'timestamp': {'value': true},
    'lists': [1, 2, 42],
    'nullable': null,
  };

  final serialized = serializers.serialize(
      BuiltMap<String, JsonObject?>.from(
          json.map((key, value) => MapEntry(key, value == null ? null : JsonObject(value)))),
      specifiedType: const FullType(
          BuiltMap, [FullType(String), FullType.nullable(JsonObject)]));

  final deserialized = BuiltMap<String, JsonObject?>(serializers.deserialize(
      serialized,
      specifiedType: const FullType(
          BuiltMap, [FullType(String), FullType.nullable(JsonObject)])));

  final unpacked =
      deserialized.map((key, value) => MapEntry(key, value?.value)).asMap();

  expect(unpacked, equals(json));
});

[ahmednfwela]

hmm, maybe the whole map should just be type JsonObject!

yes I suggest changing the property in your class to be BuiltMap<String, JsonObject?> altogether, to avoid packing/unpacking

[jimmyff]

Thanks for the null issue-noted! I'm wondering if the field can just be type JsonObject rater than a map. A bit like this:

    test('serializing and deserializing JsonObject', () {
      final json = <String, dynamic>{
        'name': 'foobar',
        'age': 99,
        'timestamp': {'value': true},
        'lists': [1, 2, 42],
      };

      final serialized = serializers.serialize(JsonObject(json),
          specifiedType: const FullType(JsonObject));

      final deserialized = serializers.deserialize(serialized,
          specifiedType: const FullType(JsonObject)) as JsonObject;

      final unpacked = BuiltMap<String, dynamic>(deserialized.value).asMap();

      expect(unpacked, equals(json));
    });

Anyway, thanks for all your help @ahmednfwela

[ahmednfwela]

@jimmyff if the data field can accept any json value (strings/numbers/lists/objects/...) then it needs to be JsonObject? if it only accepts json objects, it needs to be Map<String, JsonObject?>

[jimmyff]

@ahmednfwela Ah yes, good point, I loose typing benefits by going for the less verbose code!

[ahmednfwela]

personally I would write extension methods on Map<String,dynamic> to help pack/unpack the BuiltMap object

[jimmyff]

Ahh thats a really good idea. I'll have a play with that too thanks