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I am currently working on a Flutter project where I am trying to create a data class for a User that involves an Image property. In TypeScript, I have a union type Image that can be either a boolean or an array of { quality: string; link: string } objects. Here is the TypeScript example:

type Image = boolean | {
  quality: string;
  link: string
 }[];

type User = {
  id: string;
  name: string;
  image: Image;
};

const user1: User = {
  id: "1",
  name: "John Doe",
  image: false,
};

const user2: User = {
  id: "1",
  name: "John Doe",
  image: [
    {
      quality: "small",
      link: "https://example.com/image1",
    },
    {
      quality: "medium",
      link: "https://example.com/image2",
    },
    {
      quality: "large",
      link: "https://example.com/image3",
    },
  ],
};

Now, I want to create a similar data class for User in Dart to facilitate JSON serialization and deserialization using json_serializable.

How can I represent this union type in Dart while keeping in mind that I want to use json_serializable to generate the serialization/deserialization code for my data class? I want to have a more precise type definition for the Image property to handle both boolean and array cases appropriately.

Any help, code samples, or guidance would be greatly appreciated. Thank you!

rajput-hemant
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  • You can build your own Abstract Data Type hierarchies, but you cannot create union types in Dart (yet?). – Randal Schwartz Jul 30 '23 at 08:24
  • @RandalSchwartz Sorry about that, sir. I'm new to Dart, and I'm having a hard time working with data classes. I can't manage to create union types and make them work for JSON serialization. It would be great if you could give any insight into the same. – rajput-hemant Jul 30 '23 at 11:56

1 Answers1

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To represent the union type Image in Dart and facilitate JSON serialization and deserialization using json_serializable, you can use Dart's Union package.

o use the Union package, you need to define your union type Image as a class that extends Union2 (since it has two possible types: boolean or an array of objects). Then, you can use the @JsonUnion annotation from json_serializable to handle serialization and deserialization correctly.

Aryan Maheshwari
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  • Regarding the package to use, I couldn't find any built-in "Union" package in Dart, so I assume you are referring to an external package. Could you please clarify the name and source of the "Union" package you mentioned in your answer? Furthermore, after doing some research, I couldn't find an annotation like "@JsonUnion" in the json_annotations package either. It's possible that I might have misunderstood your suggestion, or there might be a different approach to handle union types in Dart with JSON serialization. – rajput-hemant Aug 01 '23 at 20:21
  • Also, I'd greatly appreciate it if you could provide me with a working code example or a more detailed step-by-step guide to help me understand how to define the "Image" union type as a class that extends Union2, and the correct way to handle JSON serialization and deserialization in Dart. – rajput-hemant Aug 01 '23 at 20:22