Amazon DynamoDB

Local emulators. Real API contracts. Part of Mockingbird.

Stateful Amazon DynamoDB emulator for the AWS SDK v3 low-level client and DynamoDBDocumentClient. It preserves DynamoDB attribute types while modelling CRUD, expressions, indexes, pagination, batches, transactions, TTL, streams, and conditional writes without contacting AWS.

#Install

npm install -D @crvouga/mockingbird-service-dynamodb

ESM only. Node 22+ or Bun 1.2+.

#Usage

Point the SDK's endpoint option at the emulator. Fixture SigV4 credentials are accepted.

import { DynamoDBClient } from "@aws-sdk/client-dynamodb"
import { DynamoDBDocumentClient, GetCommand } from "@aws-sdk/lib-dynamodb"
import { createServer } from "@crvouga/mockingbird-service-dynamodb/server"

// Test setup: seed the emulator and point the AWS SDK client your application uses at it.
const emulator = await createServer({
  tables: [
    {
      name: "records",
      keySchema: [{ AttributeName: "pk", KeyType: "HASH" }],
      items: [{ pk: { S: "fixture" }, status: { S: "ready" } }],
    },
  ],
})
const db = DynamoDBDocumentClient.from(
  new DynamoDBClient({
    endpoint: emulator.url,
    region: "us-east-1",
    credentials: { accessKeyId: "fixture", secretAccessKey: "fixture" },
  }),
)

// Application code: ordinary SDK calls.
const { Item } = await db.send(new GetCommand({ TableName: "records", Key: { pk: "fixture" } }))
// Item: { pk: "fixture", status: "ready" }

await emulator.close() // after the test

Supported operations are CreateTable, DescribeTable, GetItem, PutItem, UpdateItem, DeleteItem, Query, Scan, BatchGetItem, BatchWriteItem, TransactGetItems, and TransactWriteItems. The expression subset includes expression name/value aliases, SET/ADD/REMOVE/DELETE, if_not_exists, attribute_exists, attribute_not_exists, begins_with, comparisons, BETWEEN, AND/OR, projection, conditions, limits, cursors, index ordering, and return values.

#Admin and deterministic controls

• Constructor fixtures define tables, indexes, typed items, and TTL attributes.
• GET /__admin/tables, /__admin/items?table=…, and /__admin/streams?table=… inspect local state and ordered INSERT/MODIFY/REMOVE records.
• Advance the shared emulator clock to expire TTL items without sleeps.
• Fault presets are throttled and one-shot unavailable; generic fault rules can model unprocessed batch responses or eventual-read failures.

The shared runtime also provides reset, timeline, request journal, metrics, faults, and namespace isolation through x-mockingbird-namespace, /__admin/ns/<name>, or SigV4 access-key mappings.

#Deliberately not modelled

PartiQL, control-plane operations outside Create/Describe, local/global table replication, IAM policy evaluation, encryption, backups, production capacity accounting, all DynamoDB expression grammar, real asynchronous streams, dashboards, and billing are not modelled.

#API

• DynamoAPI, DynamoAPIOptions, DynamoSeedTable: AWS JSON handler and fixtures.
• AttributeValue, Item, KeySchemaElement, DynamoIndex, DynamoItem, DynamoTable, StreamRecord: typed state.
• createRuntime, DynamoRuntime, DynamoRuntimeOptions: full Mockingbird runtime.
• DYNAMODB_NAMESPACE, DYNAMODB_PRESETS, accessKeyCredential: constants and controls.
• document, operationIds, supportedOperationIds: generated OpenAPI metadata.
• createServer, DynamoServerOptions, DEFAULT_PORT, serveTarget from ./server: Node HTTP adapter and CLI integration.

Official oracle: Amazon DynamoDB API Reference.