dynamodb-data-types

A JavaScript utility to help represent DynamoDB data types and records.

New ver 4.0.0 of this library generates DynamoDB UpdateExpression. updateExpr().

Introduction

DynamoDB represents the JavaScript number 1 as {N:'1'}.

This utility helps convert between such representations.

 JavaScript             DynamoDB
------------------------------------------------
-1                {N: '-1'}
'Hello'           {S: 'Hello'}
true              {BOOL: true}
NULL              {NULL: true}
{a:1, b:''}       {M: {a: {N: '1'}, b: {S: ''}}}

Getting Started

wrap, unwrap to convert (marshall) JavaScript data.

const attr = require('dynamodb-data-types').AttributeValue;

const data = {
  id: 10,
  food: ['Rice', 33, null],
  obj: {a:1, b:true},
};

const wrapped = attr.wrap(data); // wrap (marshall) data to use with DynamoDB
/* Returns:
 * {
 *   id:{N:"10"},
 *   food:{L:[{S:"Rice"},{N:"33"},{NULL:true}]},
 *   obj:{M:{a:{N:"1"},b:{BOOL:true}}}
 * } */

attr.unwrap(wrapped); // unwrap (unmarshall) data
/* Returns:
 * {
 *   id: 10,
 *   food: ['Rice', 33, null],
 *   obj: {a:1, b:true},
 * } */

Use wrap1 and unwrap1 for single primitive values,

attr.wrap1(50);         // { N: '50' }
attr.unwrap1({N:'50'}); // 50

updateExpr() for DynamoDB UpdateExpression

Let's say you want to update color in a item or record. DynamoDB UpdateItem API requires you to provide a UpdateExpression as follows:

{
  UpdateExpression: "SET color = :a",
  ExpressionAttributeValues: {":a":{"S":"red"}}}
}

Instead of attribute color, if you want to update year to 2013 then you have to do one more step because year is a reserved keyword:

{
  UpdateExpression":"SET #A = :a",
  ExpressionAttributeValues: {":a":{S:"2013"}},
  ExpressionAttributeNames :{"#A":"year"}}
}

Use this library to generate the above for you as follows:

const { updateExpr } = require('dynamodb-data-types');
updateExpr().set({ name: 'foo' }).expr();

Below is a more comprehensive example:

const { updateExpr } = require('dynamodb-data-types');

updateExpr()             // Call updateExpr()
  .set({ a: 'foo' })     // chain multiple clauses
  .add({ n: 1 })
  .remove('rat', 'bat')
  .set({ sky: 'blue'})
  .delete({ day: ['Mon'] }) // 'day' is a reserved keyword
  .remove('hi')
  .expr(); // In the end expr() returns the UpdateExpression
// After .expr(), we cannot chain any more clauses (set,remove,add,delete)

/* Returns:
{
 * UpdateExpression: "SET a = :a, sky = :b REMOVE rat, bat, hi ADD n :c DELETE #A :d",
 * ExpressionAttributeValues: {":a":{S:"foo"},":b":{S:"blue"},":c":{N:"1"},":d":{SS:["Mon"]}},
 * ExpressionAttributeNames:{"#A":"day"}} // Because 'day' is a reserved keyword
 * } */

UpdateExpression clauses SET, REMOVE, ADD, DELETE

updateExpr().set(), remove(), add(), delete(), are the same clauses defined by DynamoDB UpdateExpression. Each clause is said to contain one or more action. See AWS documentation for more.

updateExpr() handles DynamoDB reserved keywords.

updateExpr() avoids conflict with keywords reserved by DynamoDB. To demonstrate this, the below example uses the conflicting keyword year.

A more complete example:

const { wrap } = require('dynamodb-data-types').AttributeValue;
const { updateExpr } = require('dynamodb-data-types');
const { DynamoDBClient, UpdateItemCommand, PutItemCommand } = require('@aws-sdk/client-dynamodb');
const TableName = 'FooTable';
const client = new DynamoDBClient({ region: 'us-east-1' });

const updates = updateExpr()    // Call updateExpr()
      .set({ greet: 'Hello' })  // chain multiple clauses
      .remove('foo', 'city')
      .add({ age: 1 })
      .set({ nick: 'bar' })
      .remove('baz')
      .delete({ year: [2008] }) // 'year' is a reserved keyword
      .add({ amt: 1.5 });

// Use expr() to get the UpdateExpression data structures
const { UpdateExpression,  ExpressionAttributeValues, ExpressionAttributeNames } = updates.expr();

// After .expr(), we cannot chain any more clauses (set,remove,add,delete)

/* Generated data structures:
 * {
 *   UpdateExpression:
 *    'SET greet = :a, nick = :b REMOVE foo, baz ADD age :c, amt :d DELETE #A :e',
 *
 *   ExpressionAttributeValues: {
 *     ':a': { S: 'Hello' },
 *     ':b': { S: 'bar' },
 *     ':c': { N: '1' },
 *     ':d': { N: '1.5' },
 *     ':e': { NS: [Array] }
 *   },
 *
 *   ExpressionAttributeNames: { '#A': 'year' } // Because year is a reserved keyword
 * }
 */

const params = {
  TableName,
  Key: wrap({ id: 10 }),
  UpdateExpression,
  ExpressionAttributeValues,
  ExpressionAttributeNames,
};

/* TIP: For shorter code, use ...updates.expr()
 * const params = {
 *   TableName,
 *   Key: wrap({ id: 10 }),
 *   ...updates.expr()
 * };
 */

client.send(new UpdateItemCommand(params));

updateExpr() avoids creating duplicate values

As demonstrated below, updateExpr() avoids creating duplicates in ExpressionAttributeValue by using === internally.

  /* Different action values across clauses.
   * Hence ExpressionAttributeValues has three items.
   */
  const expr0 = updateExpr()
        .set({ w: 1 })
        .set({ x: 2 })
        .add({ y: 3 })
        .expr();
  // {
  //   UpdateExpression: 'SET w = :a, x = :b ADD y :c',
  //   ExpressionAttributeValues: {
  //     ':a': { N: '1' },
  //     ':b': { N: '2' },
  //     ':c': { N: '3' },
  //   }
  // }


  /* Identical action values across clauses.
   * Hence ExpressionAttributeValues has only one item.
   */
  const expr1 = updateExpr()
        .set({ w: 1 })
        .set({ x: 1 })
        .add({ y: 1 })
        .expr();
  // {
  //   UpdateExpression: 'SET w = :a, x = :a ADD y :a',
  //   ExpressionAttributeValues: {
  //     ':a': { N: '1' }
  //   }
  // }

Roadmap TODO

To avoid duplicate values in ExpressionAttributeValues, apart from doing a strict equality check using '===', allow a deep equality to avoid duplicates.

Below, value is the same array for all actions/clauses. Hence there should be 1 entry in ExpressionAttributeValues.

However there are 3 entries.

It might be a good feature to do a deep equality and ensure 1 entry in ExpressionAttributeValues.

  const expr0 = updateExpr()
        .set({ w: [1, 2, 3] })
        .set({ x: [1, 2, 3] })
        .set({ y: [1, 2, 3] })
        .expr();
  // {
  //   UpdateExpression: 'SET w = :a, x = :b, y = :c',
  //   ExpressionAttributeValues: {
  //     ':a': { NS: ['1', '2', '3'] },
  //     ':b': { NS: ['1', '2', '3'] },
  //     ':c': { NS: ['1', '2', '3'] },
  //   }
  // }

See examples/01-put-and-update-expression.js for full example of generated DynamoDB structures UpdateExpression, ExpressionAttributeValues, ExpressionAttributeNames.

Use with Node.js

Use with AWS SDK for Node.js

npm install dynamodb-data-types

Use in cli

Use with the cli for quick utility

npm install -g dynamodb-data-types
dynamo-dt-attr-wrap '{'hello':'world'}'
dynamo-dt-attr-unwrap '{'hello': {'S': 'world'}}'

Use in the browser

Use with AWS SDK for JS in the Browser

Download the browser version from dist.

See examples/browser and this note

Notes for use in the browser

The browser version of this library (created using browserify) has not been tested. Pull requests to add tests for the browser are welcome (maybe using phantom.js?).

The browser version is available from version 2.1.2 onwards.

File size of the browser version

The browser version of this library is generated using Browserify.

For versions 3.0.0 onwards of this library, browserify is made to exclude Buffer related code. It is less likely for a browser side application to make use of Buffer as a binary type.

If you don't need detailed info about this, skip the next paragraph.

This library uses node's Buffer for recognizing binary types. By default, browserify, includes external Buffer related code, causing the filesize of the browser dist to become 5.4 times larger (6x if you compare min.js files). Version 3.0.0 onwards, browserify is made to exclude Buffer related code because it seems less likely for browser side code to detect Buffer as a binary type. Incase your browser application does require Buffer you might try using dist-with-buffer

Examples

• examples/01-put-and-update-expression.js
• examples/02-binary-image.js
• examples/03-explicit-data-type.js
• examples/04-explicit-preserve-arrays.js
• examples/browser/dynamodb-data-types.html
• examples/depricated-01-put-update.js

Features

Refer to docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_Types.html

DynamoDb-Data-Types supports:

• AttributeValue
• UpdateExpression
• ExpressionAttributeValues
• ExpressionAttributeNames
• AttributeValueUpdate (Deprecated in favour of UpdateExpression)

Supported AttributeValue types

Refer to docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_AttributeValue.html

DynamoDb-Data-Types supports:

• B
• BOOL
• BS
• L
• M
• N
• NS
• NULL
• S
• SS

preserveArrays

(New in version 2.1.0)

Consider the following:

const data = {
  alphabets: ['c', 'a', 'b', 'c']
};

wrap(data) detects alphabets as SS. Being a set SS has two properties unlike those of arrays :

• The order of elements is not preserved.
• Duplicate elements are not allowed.

Starting with version 2.1.0, you can do:

• wrap(data, {types: {alphabets: 'L'} } to explicitly tell wrap to treat it L instead of the auto-detected SS. Similarly for put() and add()
• Alternatively, call preserveArrays() to consider all arrays as type L. This has a global effect.

Read the documentation and examples for more.

Support for BOOL, NULL, M, L

(new in version 2.0.0)

DynamoDb-Data-Types version 2.0.0 introduces support for AttributeValue types BOOL, NULL, M, L.

Use of M for nested data

DynamoDb-Data-Types uses M to nest objects. Consider the following data:

const data = {
  polygon: {
    quadrilateral: {
        sides: 4
    }
  }
}

wrap() maps the above data as:

{
  'polygon': {
    'M': {
      'quadrilateral': {
        'M': {
          'sides': {
            'N': '4'
          }
        }
      }
    }
  }
}

Use of L for arrays

DynamoDb-Data-Types uses L to represent mixed arrays. Consider the following data:

{
  strs: ['abc', 'def'],
  nums: [123, 456],
  mix: [1, 'abc', true, false, null, [1,2,3]]
}

wrap() maps the above data as:

{
  strs: { 
    SS: ['abc','def'] 
  },
  nums: { 
    NS: ['123','456'] 
  },
  mix: {
    'L': [
      { N: '1' },
      { S: 'abc' },
      { BOOL: true },
      { BOOL: false },
      { NULL: true },
      { NS: ['1','2','3'] }
    ]
  }
}

Detecting data types

It is straightforward to detect types N, NS, S, SS, NULL and BOOL. To detect other types - M, L, B, BS - simple rules are applied as explained below.

For any a given value val, wrap() detects the AWS Data types as follows:

BOOL, NULL, N, S

How wrap() detects them (psuedo-code):

IF val is typeof boolean
    THEN detect as type BOOL
ELSE IF val is null
    THEN detect as type NULL
ELSE IF val is typeof number or if val instanceof Number
    THEN detect as type N
ELSE IF val is typeof string or if val is instanceof String
    THEN detect as type S

B

How wrap() detects type B (psuedo-code):

IF val is instanceof Buffer
    THEN detect as type B

There maybe other types which should get detected as B. Please let me know if you have suggestions.

M

How wrap() detects type M (psuedo-code):

IF (val is none of: BOOL, NULL, N, S, B)
    AND (typeof val === 'object')
        THEN detect as type M
ELSE
    wrap() ignores val

NS, SS, BS, L

When wrap() sees an Array, here's what it does (psuedo-code):

IF val is an Array
    IF (every element in Array is type N)
        THEN detect as type NS
    ELSE IF (every element in Array is type S)
        THEN detect as type SS
    ELSE IF (every element in Array is type B)
        THEN detect as type BS
    ELSE 
        detect as type L

API - Reference documentation

Global settings

preserveArrays()

If preserveArrays() is called, all arrays found in the object being wrapped are given type L. In other words, arrays will no longer get detected as NS, SS or BS but specified as L.

This is useful to preserve duplicates and the order of elements in arrays.

const ddt = require('dynamodb-data-types');
ddt.preserveArrays();

This function is designed to be called once - It has a global effect.

If this is not needed on a global level, a similar effect can be achieved using options parameter passed to wrap(), wrap1() and put() and add().

Similarly, the global behaviour of preserveArrays() may be overridden using the options object passed to wrap(), wrap1() and put() and add().

AttributeValue

AWS API Reference - AttributeValue

• wrap
• unwrap
• wrap1
• unwrap1

updateExpr() for DynamoDB Update

AWS API Reference - Update

• UpdateExpression
• ExpressionAttributeValues
• ExpressionAttributeNames

See updateExpr() above for detailed usage examples.

AttributeValueUpdate (Depricated)

Deprecated! Use updateExpr() instead.

To use AttributeValueUpdate (Depricated) see README-deprecated

AttributeValue

wrap(item[, options])

Wrap (marshall) JavaScript data into DynamoDB's AttributeValue data type.

Arguments

• @param {Object} item The object to wrap.
• @param {Object} options
• @return {Object} A DynamoDB AttributeValue.

Options

• types: An object containing attribute names and explicit type for that attribute. Currently explicit type can only be specified if the detected type is an array. Possible values are 'NS', 'SS', 'BS', 'L'

Example of an options object:

// Any property named 'randomList' found in the object (at any depth) is
// specified as 'NS'. This explicit type can be assigned only if `randomList` is
// detected as an array.

// Similarly if 'orderedList' is an array, it gets specified as type 'L'

{
  types: {
     randomList: 'NS', 
     orderedList: 'L'
  }
}

Example

const attr = require('dynamodb-data-types').AttributeValue;
attr.wrap({name: 'Foo', age: 50});
// {'name':{'S':'Foo'},'age':{'N':'50'}}

attr.wrap({alphabets: ['a', 'b', 'c']});
// {'alphabets':{'SS': ['a','b','c']}}

attr.wrap({alphabets: ['a', 'b', 'c']}, {types: {alphabets:'L'}});
// {'alphabets':{'L': [{'S':'a'},{'S':'b'},{'S': 'c'}]}}

unwrap(attributeValue)

Unwrap (unmarshall) DynamoDB AttributeValue to appropriate JavaScript types.

Arguments

• @param {Object} attributeValue The DynamoDB AttributeValue to unwrap.
• @return {Object} Unwrapped object with properties.

Example

const attr = require('dynamodb-data-types').AttributeValue;
attr.unwrap({'name':{'S':'Foo'},'age':{'N':'50'}});
// {name: 'Foo', age: 50}

wrap1(value [, options])

Wrap a single value into DynamoDB's AttributeValue.

Arguments

• @param {String|Number|Array}
• @param {Object} options Same as options for wrap().
• @return {Object} DynamoDB AttributeValue.

Example

const attr = require('dynamodb-data-types').AttributeValue;
attr.wrap1(50);    // {'N':'50'}
attr.wrap1('50');  // {'S':'50'}

unwrap1(attributeValue)

Unwrap a single DynamoDB's AttributeValue to a value of the appropriate JavaScript type.

Arguments

@param {Object} attributeValue The DynamoDB AttributeValue. @return {String|Number|Array} The JavaScript value.

Example

const attr = require('dynamodb-data-types').AttributeValue;
attr.unwrap1({'N':'50'});  // 50
attr.unwrap1({'S':'50'});  // '50'

Older versions of DynamoDb-Data-Types

Read this only if you need DynamoDb-Data-Types version 1.0.0 or below.

If you are already using version 1.0.0 or 0.2.7 you may continue to do so.

If you are using DynamoDb-Data-Types version 1.0.0 or 0.2.7, wrapping / unwrapping B and BS will not work when used with AWS SDK 1.x.x but should automagically work with AWS SDK 2.x.x. although it has not been tested. This is related to automatic conversion of base64 done by AWS SDK version 2.x. See AWS Upgrading Notes (1.x to 2.0).

Change log

Note: Change log dates are yyyy-mm-dd.

Version 4.0.1

2022-10-25

• fix updateExpr().remove() so that it handles reserved keywords. This fixes issue #18 (github)

Version 4.0.0

• Introduce updateExpr() to generate DynamoDB UpdateExpression used to update an item.

2021-12-19

Version 3.0.3

• Update code examples and docs

Functionally, this version is identical to the previous 3.0.2

Version 3.0.2

• Update the lodash version (used for tests).

Functionally, this version is identical to the previous 3.0.1

Version 3.0.1

• Expose as a CLI utility thanks to @bneigher (github.com/bneigher).

Functionally, apart from the CLI utility, this version is identical to the previous 3.0.0

Version 3.0.0

• For Node users, version 3.0.0 is identical to 2.1.6
• For browser side version of this library
  • In version 3.0.0 onwards Buffer related code has been excluded.
  • Filesize of the min.js version is now 6.5KB. Earlier it was 40KB.

Version 2.1.2 - 2.1.6

• Added/fixed tests to imporve coverage.
• Reviewed docs.

Source code of versions 2.1.2 to 2.1.6 are identical to 2.1.1.

Version 2.1.2

This version is identical to 2.1.1 with no changes to code. It only includes a JS build for the browser plus a few more tests.

• Use browserify to create a dist for use in the browser.
• Updated tests, use travis-ci, coverage, istanbul, .jshintrc.

Version 2.1.1

2015-12-18

• Replace functions deprecated by Node.

Version 2.1.0

2015-08-17

• Call preserveArrays() to use type L for array types; this preserves order of array elements and allows duplicate array elements both of which are not possible using sets SS, NS or BS
• If not required on a global scale (calling preserveArrays), explicity set array types by passing opts to wrap(), add(), put()

Version 2.0.1

2015-02-15

• Fixed README
• Committed modified package.json (just realised it wasn't committed)

Version 2.0.0

2015-02-15

• Implemnted M
• Implemented L
• Added example to put and get binary data (examples/02-binary-image.js)

Version 1.0.0

2015-02-11

Note: There are no source code changes in version 1.0.0. Functionally, 1.0.0 is identical to 0.2.7.

• Bumped from version 0.2.7 to version 1.0.0.
• Update documentation especially with regard to B and BS data types.
• Added development deps into pacakge.json instead of tests/package.json (It should have been this way to begin with)

version 0.2.7

2014-01-29

version 0.2.6

2013-11-15

version 0.2.5

2013-11-11

License

License