MockDb

The MockDb class wires up a local JSON data store to replicate some key behaviors of DynamoDB for testing purposes.

MockDb is not a database in any meaningful sense, nor does it express anything like the full range of DynamoDB's features! It's just a limited test fixture, to which I add features as I need them.

The current feature set includes:

• query & querySync - Depending on the options passed, these methods behave like either a DynamoDB query or scan operation, including limited return sets with page keys.

• All methods exist in synchronous & asynchronous versions. Async methods run with a normally-distributed delay.

That's it!

MockDB depends on entity-tools to define entity properties, indexable properties, and records. This package also provides the sort function used internally by MockDb.query.

Usage

You'll almost certainly run MockDb as a dev dependency. To install:

npm i -D @karmaniverous/mock-db
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Then you can run:

import type { Entity } from '@karmaniverous/entity-tools';

import { MockDb, type QueryOptions } from '.';

// Specify the data type.
interface User extends Entity {
  partition: string;
  id: number;
  name: string;
}

// Create some data.
const users: User[] = [
  { partition: 'a', id: 4, name: 'Alice' },
  { partition: 'b', id: 3, name: 'Bob' },
  { partition: 'a', id: 2, name: 'Charlie' },
  { partition: 'a', id: 1, name: 'Dave' },
];

// Create a new instance of MockDb.
const mockDb = new MockDb(users);

// Perform a "scan" synchronously across partitions with a filter.
const scanResult = mockDb.querySync({
  filter: ({ id }) => id > 2,
  sortOrder: [{ property: 'id' }],
});

console.log(scanResult);

// {
//   count: 2,
//   items: [
//     { partition: 'b', id: 2, name: 'Bob' },
//     { partition: 'a', id: 3, name: 'Alice' }
//   ],
//   pageKey: undefined
// }

// Perform an asynchronous, paged, sorted "query" within a partition.
const queryOptions: QueryOptions<User> = {
  hashKey: 'partition',
  hashValue: 'a',
  indexComponents: ['partition', 'id'],
  limit: 2,
  sortOrder: [{ property: 'id' }],
};

let queryResult = await mockDb.query(queryOptions, 100);

console.log(queryResult);

// {
//   count: 2,
//   items: [
//     { partition: 'a', id: 1, name: 'Dave' },
//     { partition: 'a', id: 2, name: 'Charlie' }
//   ],
//   pageKey: { partition: 'a', id: 2 }
// }

// Use the returned pageKey to get the next page.
queryResult = await mockDb.query(
  {
    ...queryOptions,
    pageKey: queryResult.pageKey,
  },
  100,
);

console.log(queryResult);

// {
//   count: 1,
//   items: [ { partition: 'a', id: 4, name: 'Alice' } ],
//   pageKey: undefined
// }
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See the API Documentation for more details.

Got questions or suggestions? Start a discussion!

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