How to save this nested class in Isar DB Flutter - flutter

Question

I have the following 4 classes. In this, only the ProductGroup is saved, ProductVariant, ProductSize and ProductColor are not stored. Please help me with this.
product_group.dart
#Collection()
class ProductGroup {
late Id id;
#Index(caseSensitive: false)
late String productGroupName;
final productVariants = IsarLinks<ProductVariant>();
ProductGroup();
ProductGroup.fromJson(Map<String, dynamic> json) {
id = json['Id'];
productGroupName = json['PG'];
if (json['Ps'] != null) {
json['Ps'].forEach((variant) {
productVariants.add(ProductVariant.fromJson(variant));
});
}
}
Map<String, dynamic> toJson() {
final Map<String, dynamic> data = <String, dynamic>{};
data['Id'] = id;
data['PG'] = productGroupName;
data['Ps'] = productVariants.map((variant) => variant.toJson()).toList();
return data;
}
}
product_variant.dart
#Collection()
class ProductVariant {
late Id id;
late String variantName;
final productSizes = IsarLinks<ProductSize>();
ProductVariant();
ProductVariant.fromJson(Map<String, dynamic> json) {
id = json['Id'];
variantName = json['St'];
if (json['Ss'] != null) {
json['Ss'].forEach((v) {
productSizes.add(ProductSize.fromJson(v));
});
}
}
Map<String, dynamic> toJson() {
final Map<String, dynamic> data = <String, dynamic>{};
data['Id'] = id;
data['St'] = variantName;
data['Ss'] = productSizes.map((v) => v.toJson()).toList();
return data;
}
}
product_size.dart
#Collection()
class ProductSize {
late Id id;
late String size;
final productColors = IsarLinks<ProductColor>();
ProductSize();
ProductSize.fromJson(Map<String, dynamic> json) {
id = json['Id'];
size = json['S'];
if (json['Cs'] != null) {
json['Cs'].forEach((v) {
productColors.add(ProductColor.fromJson(v));
});
}
}
Map<String, dynamic> toJson() {
final Map<String, dynamic> data = <String, dynamic>{};
data['Id'] = id;
data['S'] = size;
data['Cs'] = productColors.map((color) => color.toJson()).toList();
return data;
}
}
product_color.dart
#Collection()
class ProductColor {
late Id id;
late String colorName;
late String colorHexCode;
ProductColor();
ProductColor.fromJson(Map<String, dynamic> json) {
id = json['Id'];
colorName = json['C'];
colorHexCode = json['CC'];
}
Map<String, dynamic> toJson() {
final Map<String, dynamic> data = <String, dynamic>{};
data['Id'] = id;
data['C'] = colorName;
data['CC'] = colorHexCode;
return data;
}
}
I am parsing the json and saving it in Isar
convertJsonToIsar() async {
try {
// For testing purposes, loading Json from assets, in Prod, Json will be fetched from server
final String response = await rootBundle.loadString('assets/pr_dump.json');
final data = await json.decode(response);
List<ProductGroup> productGroupList = [];
data.forEach((item) {
productGroupList.add(ProductGroup.fromJson(item));
});
Isar _isar = getIsar();
_isar.writeTxnSync(() {
_isar.productGroups.putAllSync(productGroupList, saveLinks: true);
});
} catch (e) {
// Handle Error
print('Caught Error');
print(e.toString());
return 0;
}
}
Only the ProductGroup is stored, ProductVariant, ProductSize and ProductColor are not stored. Please help me with this.