dynamo-converters

A collection of converter functions to get good old JavaScript key/value objects into a DynamoDB friendly schema and back again.

Functionality

Amazon's official aws-sdk for JavaScript uses a relatively verbose data structure to put, update or delete items stored inside a DynamoDB table. This is necessary to cover all possible use cases. But most of the time a much simpler data structure does the job as well. This little package is made for those cases.

If you think the official SDK is too verbose but this package does not cover all your needs you might want to take a look at dynamodb-data-types by kayomarz.

Getting Started

This package is available on npm and can be installed as usual:

npm install dynamo-converters

You can then use dynamo-converters by importing it:

import { addValue, dataToItem, deltaToUpdateParams, itemToData } from 'dynamo-converters';

Documentation

dynamo-converters does provide three functions:

item : dataToItem( data )

This function takes a plain JavaScript object as input and returns a structured item which can then be used with the official SDK.

const data = {
    object: {
        nothing: undefined,
        number: 2,
        string: 'lorem ipsum'
    }
};

console.log(dataToItem(data));

// {
//     object: {
//         M: {
//             number: { N: '2' },
//             string: { S: 'lorem ipsum' }
//         }
//     }
// }

Please have a look at the unit tests for more examples.

This function is similar to the marshall() function provided by the @aws-sdk/util-dynamodb package but it preserves the property types.

dataToItem({ a: 0 });
// {
//     a: {
//         N: string;
//     };
// }

marshall({ a: 0 });
// {
//     [key: string]: any;
// }

updateParams : deltaToUpdateParams( delta )

This function takes a plain JavaScript object as input and returns all necessary update params which can then be used with the official SDK.

deltaToUpdateParams() also takes care of reserved words and populates the expressionAttributeNames property of the returned object if needed. If the delta contains no reserved word this property will be missing.

const delta = {
    nothing: undefined,
    object: {
        number: 2,
        string: 'lorem ipsum'
    }
};

console.log(deltaToUpdateParams(delta));

// {
//     ExpressionAttributeNames: {
//         '#object': 'object'
//     },
//     ExpressionAttributeValues: {
//         ':object': {
//             M: {
//                 number: {
//                     N: '2'
//                 },
//                 string: {
//                     S: 'lorem ipsum'
//                 }
//             }
//         }
//     },
//     UpdateExpression: 'REMOVE nothing SET #object = :object'
// }

The addValue() function can be used to define an ADD action.

const delta = {
    counter: addValue(3)
};

console.log(deltaToUpdateParams(delta));

// {
//     ExpressionAttributeNames: {
//         '#counter': 'counter'
//     },
//     ExpressionAttributeValues: {
//         ':counter': {
//             N: '3'
//         }
//     },
//     UpdateExpression: 'ADD #counter = :counter'
// }

Please have a look at the unit tests for more examples.

data : itemToData( item )

This function takes a structured item returned by the official SDK and turns it into a plain JavaScript object.

const item = {
    object: {
        M: {
            number: { N: '2' },
            string: { S: 'lorem ipsum' }
        }
    }
};

console.log(itemToData(item));

// {
//     object: {
//         number: 2,
//         string: 'lorem ipsum'
//     }
// }

Please have a look at the unit tests for more examples.

This function is similar to the unmarshall() function provided by the @aws-sdk/util-dynamodb package but it preserves the property types.

itemToData({ a: { N: '1' } });
// {
//     a: number;
// }

unmarshall({ a: { N: '1' } });
// {
//     [key: string]: any;
// }