Dynameh

DynamoDB on Node more easier

Dynameh works with the existing DynamoDB JavaScript API and its objects rather than wrapping them and hiding the details. The goal is to make the existing API easier to work with where naturally possible, without ever limiting its power. Obscure and rarely used flags are still accessible while common operations are quicker to write.

Dynameh makes it easier to:

• build request objects
• unwrap response objects
• run large batch requests
• run requests concurrently that can't be run in batch
• implement optimistic locking
• configure Date serialization

Installation

Dynameh is your typical NPM package.

npm install --save dynameh

Usage

import * as dynameh from "dynameh";
// or
const dynameh = require("dynameh");

See the documentation for details on each module and its methods.

A Simple Example

This example is written using async/await which is available in TypeScript and Babel.

import * as aws from "aws-sdk";
import * as dynameh from "dynameh";

// Initialize the DynamoDB client.
const dynamodb = new aws.DynamoDB({
    apiVersion: "2012-08-10",
    region: "us-west-1"
});

// Set up the table schema.
const tableSchema = {
    tableName: "motorcycles",
    primaryKeyField: "id",
    primaryKeyType: "string"
};

async function updateMotorcycleHorsePower(motorcycleId, bhp) {
    // Fetch the item from the database.
    const getRequest = dynameh.requestBuilder.buildGetInput(tableSchema, motorcycleId);
    const getResult = await dynamodb.getItem(getRequest).promise();
    let motorcycle = dynameh.responseUnwrapper.unwrapGetOutput(getResult);
    
    if (!motorcycle) {
        // Item not found, create it.
        motorcycle = {
            id: motorcycleId
        };
    }
    
    // Update the horse power stat.
    motorcycle.bhp = bhp;
    
    // Put the updated object in the database.
    const putRequest = dynameh.requestBuilder.buildPutInput(tableSchema, motorcycle);
    await dynamodb.putItem(putRequest).promise();
}

updateMotorcycleHorsePower("sv-650", 73.4);

TableSchema

The key to easy building of requests in Dynameh is the TableSchema. This simple object defines all the extra information Dynameh needs to build requests.

For a table called MyTable with a primary key id that is a number...

{
  "tableName": "MyTable",
  "primaryKeyField": "id",
  "primaryKeyType": "number"
}

For a table called MyAdvancedTable with a primary key id that is a string, a range key date that is a number, and a version field version...

{
  "tableName": "MyAdvancedTable",
  "primaryKeyField": "id",
  "primaryKeyType": "string",
  "sortKeyField": "date",
  "sortKeyType": "number",
  "versionKeyField": "version"
}

Optimistic Locking

Optimistic locking is a strategy for preventing changes from clobbering each other. For example two processes read from the database, make unrelated changes, and then both write to the database but the second write overwrites the first (clobbers).

Enable optimistic locking by setting the versionKeyField on your TableSchema. In the second TableSchema example that field is version. The versionKeyField will be automatically incremented on the server side during a put request. If the value for versionKeyField sent does not match the current value in the database then the contents have changed since the last get and the optimistic lock has failed. In that case you should get the latest version from the database and replay the update against that.

import * as aws from "aws-sdk";
import * as dynameh from "dynameh";

// Initialize the DynamoDB client.
const dynamodb = new aws.DynamoDB({
    apiVersion: "2012-08-10",
    region: "us-west-1"
});

// Set up the table schema.
const tableSchema = {
    tableName: "motorcycles",
    primaryKeyField: "id",
    primaryKeyType: "string",
    versionKeyField: "version"
};

async function updateMotorcycleHorsePower(motorcycleId, bhp) {
    // Fetch the item from the database.
    const getRequest = dynameh.requestBuilder.buildGetInput(tableSchema, motorcycleId);
    const getResult = await dynamodb.getItem(getRequest).promise();
    let motorcycle = dynameh.responseUnwrapper.unwrapGetOutput(getResult);
    
    if (!motorcycle) {
        // Item not found, create it.
        // Note that we don't need to set the version on create.
        motorcycle = {
            id: motorcycleId
        };
    }
    
    // Update the horse power stat.
    motorcycle.bhp = bhp;
    
    // Put the updated object in the database.
    const putRequest = dynameh.requestBuilder.buildPutInput(tableSchema, motorcycle);
    try {
        await dynamodb.putItem(putRequest).promise();
    } catch (err) {
        if (err.code === "ConditionalCheckFailedException") {
            // If this is the error code then the optimistic locking has failed
            // and we should redo the update operation (done here with recursion).
            updateMotorcycleHorsePower(motorcycleId, bhp);
        } else {
            throw err;
        }
    }
}

updateMotorcycleHorsePower("sv-650", 73.4);

Date Serialization

Date serialization can be configured by setting dateSerializationFunction on your TableSchema. It's a function that takes in a Date and returns a string or number. By default Dates are serialized as ISO-8601 strings.

For example...

const tableSchema = {
    tableName: "MyTable",
    primaryKeyField: "id",
    primaryKeyType: "number",
    dateSerializationFunction: date => date.toISOString()   // same as default
}