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A schema-based data mapper for Amazon DynamoDB.
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README.md

Amazon DynamoDB DataMapper For JavaScript

Apache 2 License

This repository hosts several packages that collectively make up an object to document mapper for JavaScript applications using Amazon DynamoDB.

Getting started

The @aws/dynamodb-data-mapper package provides a simple way to persist and load an application's domain objects to and from Amazon DynamoDB. When used together with the decorators provided by the @aws/dynamodb-data-mapper-annotations package, you can describe the relationship between a class and its representation in DynamoDB by adding a few decorators:

import {
    attribute,
    hashKey,
    rangeKey,
    table,
} from '@aws/dynamodb-data-mapper-annotations';

@table('table_name')
class MyDomainObject {
    @hashKey()
    id: string;

    @rangeKey({defaultProvider: () => new Date()})
    createdAt: Date;

    @attribute()
    completed?: boolean;
}

With domain classes defined, you can interact with records in DynamoDB via an instance of DataMapper:

import {DataMapper} from '@aws/dynamodb-data-mapper';
import DynamoDB = require('aws-sdk/clients/dynamodb');

const mapper = new DataMapper({
    client: new DynamoDB({region: 'us-west-2'}), // the SDK client used to execute operations
    tableNamePrefix: 'dev_' // optionally, you can provide a table prefix to keep your dev and prod tables separate
});

Supported operations

Using the mapper object and MyDomainObject class defined above, you can perform the following operations:

put

Creates (or overwrites) an item in the table

const toSave = Object.assign(new MyDomainObject, {id: 'foo'});
mapper.put(toSave).then(objectSaved => {
    // the record has been saved
});

get

Retrieves an item from DynamoDB

mapper.get(Object.assign(new MyDomainObject, {id: 'foo', createdAt: new Date(946684800000)}))
    .then(myItem => {
        // the item was found
    })
    .catch(err => {
        // the item was not found
    })

NB: The promise returned by the mapper will be rejected with an ItemNotFoundException if the item sought is not found.

update

Updates an item in the table

const myItem = await mapper.get(Object.assign(
    new MyDomainObject,
    {id: 'foo', createdAt: new Date(946684800000)}
));
myItem.completed = true;

await mapper.update(myItem);

delete

Removes an item from the table

await mapper.delete(Object.assign(
    new MyDomainObject,
    {id: 'foo', createdAt: new Date(946684800000)}
));

scan

Lists the items in a table or index

for await (const item of mapper.scan(MyDomainObject)) {
    // individual items will be yielded as the scan is performed
}

// Optionally, scan an index instead of the table:
for await (const item of mapper.scan(MyDomainObject, {indexName: 'myIndex'})) {
    // individual items will be yielded as the scan is performed
}

query

Finds a specific item (or range of items) in a table or index

for await (const foo of mapper.query(MyDomainObject, {id: 'foo'})) {
    // individual items with a hash key of "foo" will be yielded as the query is performed
}

Batch operations

The mapper also supports batch operations. Under the hood, the batch will automatically be split into chunks that fall within DynamoDB's limits (25 for batchPut and batchDelete, 100 for batchGet). The items can belong to any number of tables, and exponential backoff for unprocessed items is handled automatically.

batchPut

Creates (or overwrites) multiple items in the table

const toSave = [
    Object.assign(new MyDomainObject, {id: 'foo', completed: false}),
    Object.assign(new MyDomainObject, {id: 'bar', completed: false})
];
for await (const persisted of mapper.batchPut(toSave)) {
    // items will be yielded as they are successfully written
}
batchGet

Fetches multiple items from the table

const toGet = [
    Object.assign(new MyDomainObject, {id: 'foo', createdAt: new Date(946684800000)}),
    Object.assign(new MyDomainObject, {id: 'bar', createdAt: new Date(946684800001)})
];
for await (const found of mapper.batchGet(toGet)) {
    // items will be yielded as they are successfully retrieved
}

NB: Only items that exist in the table will be retrieved. If a key is not found, it will be omitted from the result.

batchDelete

Removes multiple items from the table

const toRemove = [
    Object.assign(new MyDomainObject, {id: 'foo', createdAt: new Date(946684800000)}),
    Object.assign(new MyDomainObject, {id: 'bar', createdAt: new Date(946684800001)})
];
for await (const found of mapper.batchDelete(toRemove)) {
    // items will be yielded as they are successfully removed
}

Operations with Expressions

Aplication example
import {
    AttributePath,
    FunctionExpression,
    UpdateExpression,
} from '@aws/dynamodb-expressions';

const expr = new UpdateExpression();

// given the anotation bellow
@table('tableName')
class MyRecord {
    @hashKey()
    email?: string;

    @attribute()
    passwordHash?: string;

    @attribute()
    passwordSalt?: string;

    @attribute()
    verified?: boolean;

    @attribute()
    verifyToken?: string;
}

// you make a mapper operation as follows
const aRecord = Object.assign(new MyRecord(), {
    email,
    passwordHash: password,
    passwordSalt: salt,
    verified: false,
    verifyToken: token,
});
mapper.put(aRecord, { 
    condition: new FunctionExpression('attribute_not_exists', new AttributePath('email') 
}).then( /* result handler */ );

Table lifecycle operations

createTable

Creates a table for the mapped class and waits for it to be initialized:

mapper.createTable(MyDomainObject, {readCapacityUnits: 5, writeCapacityUnits: 5})
    .then(() => {
        // the table has been provisioned and is ready for use!
    })
ensureTableExists

Like createTable, but only creates the table if it doesn't already exist:

mapper.ensureTableExists(MyDomainObject, {readCapacityUnits: 5, writeCapacityUnits: 5})
    .then(() => {
        // the table has been provisioned and is ready for use!
    })
deleteTable

Deletes the table for the mapped class and waits for it to be removed:

await mapper.deleteTable(MyDomainObject)
ensureTableNotExists

Like deleteTable, but only deletes the table if it exists:

await mapper.ensureTableNotExists(MyDomainObject)

Constituent packages

The DataMapper is developed as a monorepo using lerna. More detailed documentation about the mapper's constituent packages is available by viewing those packages directly.

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