util-dynamodb convertToAttr throws error when trying to serialize ES6 classes

[trivikr]

Describe the bug
util-dynamodb convertToAttr throws error when trying to serialize ES6 classes
Refs: #1531 (comment)

SDK version number
master

Is the issue in the browser/Node.js/ReactNative?
N/A

To Reproduce (observed behavior)
A unit test is added under unsupported type in PR #1531

Expected behavior
Questionable, as v2 DynamodDB serializes ES6 class objects as maps.

Storing as string using JSON.stringify is more helpful, as class properties can be deserialized using JSON.parse:

• Example StackOverflow discussion: https://stackoverflow.com/a/40201783
• MDN: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify

JSON.stringify will also store Date (ref: #1534) in ISO 8601 format as follows:

> const now = new Date();
> const serialized = JSON.stringify(now);
> const past = new Date(JSON.parse(serialized));
> now.getTime() === past.getTime()
true

[russell-dot-js]

IMO it might be nice if we expose an interface similar to the Go dynamo SDK

export interface DynamoSerializable {
  toDynamoDB: () => any;
}

Then in document client, prior to converting to attribute values:

function isDynamoSerializable<T>(value: T): T is DynamoSerializable {
  return !!((T as DynamoSerializable).toDynamoDB);
}

const valueToConvert = isDynamoSerializable(value) ?
  value.toDynamoDB() :
  value;

const attrs = convertToAttr(valueToConvert);

[trivikr]

The comment by @russell-dot-js seems to be a better solution where user provides us with serialization function for class objects.

Verified by using serialize and deserialize methods from class-transformer in the code below:

import { deepStrictEqual } from "assert";
import { serialize, deserialize } from "class-transformer";
import { AttributeValue } from "@aws-sdk/client-dynamodb";

interface DynamoSerializable {
  toDynamoDB: () => AttributeValue;
}

class UserClass implements DynamoSerializable {
  constructor(private firstName: string, private lastName: string) {}

  toDynamoDB() {
    return { S: serialize(this) };
  }
}

const userFromStr = (str: string) => deserialize(UserClass, str);

const userClassObj = new UserClass("firstName", "lastName");
const serialized = userClassObj.toDynamoDB();
const deserializedObj = userFromStr(serialized.S);

deepStrictEqual(userClassObj, deserializedObj); // doesn't throw AssertionError

EDIT: modified DynamoSerializable.toDynamoDB() to return AttributeValue

[trivikr]

As originally suggested by @russell-dot-js, since toDynmaoDB() will be called from marshall function which is util-dynamodb, we can enforce returning NativeAttributeValue instead, as follows:

import { deepStrictEqual } from "assert";
import { serialize, deserialize } from "class-transformer";
import { NativeAttributeValue } from "@aws-sdk/util-dynamodb";

interface DynamoSerializable {
  toDynamoDB: () => NativeAttributeValue;
}

class UserClass implements DynamoSerializable {
  constructor(private firstName: string, private lastName: string) {}

  // returns string which is NativeAttributeValue
  toDynamoDB() {
    return serialize(this);
  }
}

const userFromStr = (str: string) => deserialize(UserClass, str);

const userClassObj = new UserClass("firstName", "lastName");
const serialized = userClassObj.toDynamoDB();
const deserializedObj = userFromStr(serialized);

deepStrictEqual(userClassObj, deserializedObj);

[russell-dot-js]

The comment by @russell-dot-js seems to be a better solution where user provides us with serialization function for class objects.

Verified by using serialize and deserialize methods from class-transformer in the code below:

import { deepStrictEqual } from "assert";
import { serialize, deserialize } from "class-transformer";
import { AttributeValue } from "@aws-sdk/client-dynamodb";

interface DynamoSerializable {
  toDynamoDB: () => AttributeValue;
}

class UserClass implements DynamoSerializable {
  constructor(private firstName: string, private lastName: string) {}

  toDynamoDB() {
    return { S: serialize(this) };
  }
}

const userFromStr = (str: string) => deserialize(UserClass, str);

const userClassObj = new UserClass("firstName", "lastName");
const serialized = userClassObj.toDynamoDB();
const deserializedObj = userFromStr(serialized.S);

deepStrictEqual(userClassObj, deserializedObj); // doesn't throw AssertionError

EDIT: modified DynamoSerializable.toDynamoDB() to return AttributeValue

@trivikr I dig it, but just keep in mind that most consumers will not be using ES6 classes for their DTO's, most JS teams tend to use native JS objects over classes. For us, at least, we only use ES6 classes when necessary, e.g. to use Typescript decorators. But we only use them when we must, not because we want to (they're quite despisable IMHO).

I think we can generally solve everything by allowing consumers to pass custom parse/transform functions to the document client, while implementing this interface will solve some problems, it might be a bit niche and redundant with the other solution in place.

[trivikr]

I think we can generally solve everything by allowing consumers to pass custom parse/transform functions to the document client, while implementing this interface will solve some problems, it might be a bit niche and redundant with the other solution in place.

@russell-dot-js Did you mean something like the premarshall configuration suggested in #1533?

[trivikr]

Update: we're exploring serializing of ES6 classes and more using premarshalling at #1533 (comment)

[trivikr]

As discussed in #1533 (comment), we'll be adding support to marshall all Objects by passing a configuration (say marshallObjects) in marshall function.

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