feature request: support discriminated union type

[tylim88]

currently the library does not support discriminated union, which is a very useful pattern in TS

can we do something like:

		attributes: {
			animal: {
				type: 'discriminated union',
                                 unions:{
                                      fish:{
                                          type:'map',
                                          properties:{
                                                 habitat:{
                                                      type: 'lake'
                                                 }
                                          }
                                      dog:{
                                          type:'map',
                                          properties:{
                                                 habitat:{
                                                      type: 'land'
                                                 }
                                          }
                                     }
                                }
			},
		}

?

[anatolzak]

An existing solution is to use CustomAttributeType along with the TypeScript type of the discriminated union. The only downside is the lack of runtime validation for custom attributes. However, you can specify your own validation callback.

Here is an example of using CustomAttributeType from the documentation:

import { Entity, CustomAttributeType } from "electrodb";

const table = "workplace_table";

type PersonnelRole =
  | {
      type: "employee";
      startDate: number;
      endDate?: number;
    }
  | {
      type: "contractor";
      contractStartDate: number;
      contractEndDate: number;
    };

const person = new Entity(
  {
    model: {
      entity: "personnel",
      service: "workplace",
      version: "1",
    },
    attributes: {
      id: {
        type: "string",
      },
      role: {
        type: CustomAttributeType<PersonnelRole>("any"),
        required: true,
      },
    },
    indexes: {
      record: {
        pk: {
          field: "pk",
          composite: ["id"],
        },
        sk: {
          field: "sk",
          composite: [],
        },
      },
    },
  },
  { table },
);

[tylim88]

hi is custom attribute type possible with top level field?