@aws/dynamodb-query-iterator

Abstraction for DynamoDB queries and scans that handles pagination and parallel worker coordination

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Amazon DynamoDB Query and Scan Iteration

Apache 2 License

This library provides utilities for automatically iterating over all DynamoDB records returned by a query or scan operation using async iterables. Each iterator and paginator included in this package automatically tracks DynamoDB metadata and supports resuming iteration from any point within a full query or scan.

Paginators

Paginators are asynchronous iterables that yield each page of results returned by a DynamoDB query or scan operation. For sequential paginators, each invocation of the next method corresponds to an invocation of the underlying API operation until all no more pages are available.

QueryPaginator

Retrieves all pages of a DynamoDB query in order.

Example usage

import { QueryPaginator } from '@aws/dynamodb-query-iterator';
import DynamoDB = require('aws-sdk/clients/dynamodb');

const paginator = new QueryPaginator(
    new DynamoDB({region: 'us-west-2'}),
    {
        TableName: 'my_table',
        KeyConditionExpression: 'partitionKey = :value',
        ExpressionAttributeValues: {
            ':value': {S: 'foo'}
        },
        ReturnConsumedCapacity: 'INDEXES'
    }
);

for await (const page of paginator) {
    // do something with `page`
}

// Inspect the total number of items yielded
console.log(paginator.count);

// Inspect the total number of items scanned by this operation
console.log(paginator.scannedCount);

// Inspect the capacity consumed by this operation 
// This will only be available if `ReturnConsumedCapacity` was set on the input
console.log(paginator.consumedCapacity);

Suspending and resuming queries

You can suspend any running query from within the for loop by using the break keyword. If there are still pages that have not been fetched, the lastEvaluatedKey property of paginator will be defined. This can be provided as the ExclusiveStartKey for another QueryPaginator instance:

import { QueryPaginator } from '@aws/dynamodb-query-iterator';
import { QueryInput } from 'aws-sdk/clients/dynamodb';
import DynamoDB = require('aws-sdk/clients/dynamodb');

const dynamoDb = new DynamoDB({region: 'us-west-2'});
const input: QueryInput = {
    TableName: 'my_table',
    KeyConditionExpression: 'partitionKey = :value',
    ExpressionAttributeValues: {
        ':value': {S: 'foo'}
    },
    ReturnConsumedCapacity: 'INDEXES'
};

const paginator = new QueryPaginator(dynamoDb, input);

for await (const page of paginator) {
    // do something with the first page of results
    break
}

for await (const page of new QueryPaginator(dynamoDb, {
    ...input,
    ExclusiveStartKey: paginator.lastEvaluatedKey
})) {
    // do something with the remaining pages
}

Suspending and resuming the same paginator instance is not supported.

ScanPaginator

Retrieves all pages of a DynamoDB scan in order.

Example usage

import { ScanPaginator } from '@aws/dynamodb-query-iterator';
import DynamoDB = require('aws-sdk/clients/dynamodb');

const paginator = new ScanPaginator(
    new DynamoDB({region: 'us-west-2'}),
    {
        TableName: 'my_table',
        ReturnConsumedCapacity: 'INDEXES'
    }
);

for await (const page of paginator) {
    // do something with `page`
}

// Inspect the total number of items yielded
console.log(paginator.count);

// Inspect the total number of items scanned by this operation
console.log(paginator.scannedCount);

// Inspect the capacity consumed by this operation 
// This will only be available if `ReturnConsumedCapacity` was set on the input
console.log(paginator.consumedCapacity);

Suspending and resuming scans

You can suspend any running scan from within the for loop by using the break keyword. If there are still pages that have not been fetched, the lastEvaluatedKey property of paginator will be defined. This can be provided as the ExclusiveStartKey for another ScanPaginator instance:

import { ScanPaginator } from '@aws/dynamodb-query-iterator';
import { ScanInput } from 'aws-sdk/clients/dynamodb';
import DynamoDB = require('aws-sdk/clients/dynamodb');

const dynamoDb = new DynamoDB({region: 'us-west-2'});
const input: ScanInput = {
    TableName: 'my_table',
    ReturnConsumedCapacity: 'INDEXES'
};

const paginator = new ScanPaginator(dynamoDb, input);

for await (const page of paginator) {
    // do something with the first page of results
    break
}

for await (const page of new ScanPaginator(dynamoDb, {
    ...input,
    ExclusiveStartKey: paginator.lastEvaluatedKey
})) {
    // do something with the remaining pages
}

Suspending and resuming the same paginator instance is not supported.

ParallelScanPaginator

Retrieves all pages of a DynamoDB scan utilizing a configurable number of scan segments that operate in parallel. When performing a parallel scan, you must specify the total number of segments you wish to use, and neither an ExclusiveStartKey nor a Segment identifier may be included with the input provided.

Example usage

import { ParallelScanPaginator } from '@aws/dynamodb-query-iterator';
import DynamoDB = require('aws-sdk/clients/dynamodb');

const paginator = new ParallelScanPaginator(
    new DynamoDB({region: 'us-west-2'}),
    {
        TableName: 'my_table',
        TotalSegments: 4,
        ReturnConsumedCapacity: 'INDEXES'
    }
);

for await (const page of paginator) {
    // do something with `page`
}

// Inspect the total number of items yielded
console.log(paginator.count);

// Inspect the total number of items scanned by this operation
console.log(paginator.scannedCount);

// Inspect the capacity consumed by this operation 
// This will only be available if `ReturnConsumedCapacity` was set on the input
console.log(paginator.consumedCapacity);

Suspending and resuming parallel scans

You can suspend any running scan from within the for loop by using the break keyword. If there are still pages that have not been fetched, the scanState property of interrupted paginator can be provided to the constructor of another ParallelScanPaginator instance:

import { 
    ParallelScanInput,
    ParallelScanPaginator,
} from '@aws/dynamodb-query-iterator';
import DynamoDB = require('aws-sdk/clients/dynamodb');

const client = new DynamoDB({region: 'us-west-2'});
const input: ParallelScanInput = {
    TableName: 'my_table',
    TotalSegments: 4,
    ReturnConsumedCapacity: 'INDEXES'
};

const paginator = new ParallelScanPaginator(client, input);

for await (const page of paginator) {
    // do something with the first page of results
    break
}

for await (const page of new ParallelScanPaginator(
    client,
    input,
    paginator.scanState
)) {
    // do something with the remaining pages
}

Suspending and resuming the same paginator instance is not supported.

Iterators

Iterators are asynchronous iterables that yield each of record returned by a DynamoDB query or scan operation. Each invocation of the next method may invoke the underlying API operation until all no more pages are available.

QueryIterator

Retrieves all records of a DynamoDB query in order.

Example usage

import { QueryIterator } from '@aws/dynamodb-query-iterator';
import DynamoDB = require('aws-sdk/clients/dynamodb');

const iterator = new QueryIterator(
    new DynamoDB({region: 'us-west-2'}),
    {
        TableName: 'my_table',
        KeyConditionExpression: 'partitionKey = :value',
        ExpressionAttributeValues: {
            ':value': {S: 'foo'}
        },
        ReturnConsumedCapacity: 'INDEXES'
    },
    ['partitionKey']
);

for await (const record of iterator) {
    // do something with `record`
}

// Inspect the total number of items yielded
console.log(iterator.count);

// Inspect the total number of items scanned by this operation
console.log(iterator.scannedCount);

// Inspect the capacity consumed by this operation 
// This will only be available if `ReturnConsumedCapacity` was set on the input
console.log(iterator.consumedCapacity);

ScanIterator

Retrieves all records of a DynamoDB scan in order.

Example usage

import { ScanIterator } from '@aws/dynamodb-query-iterator';
import DynamoDB = require('aws-sdk/clients/dynamodb');

const iterator = new ScanIterator(
    new DynamoDB({region: 'us-west-2'}),
    {
        TableName: 'my_table',
        ReturnConsumedCapacity: 'INDEXES'
    },
    ['partitionKey', 'sortKey']
);

for await (const record of iterator) {
    // do something with `record`
}

// Inspect the total number of items yielded
console.log(iterator.count);

// Inspect the total number of items scanned by this operation
console.log(iterator.scannedCount);

// Inspect the capacity consumed by this operation 
// This will only be available if `ReturnConsumedCapacity` was set on the input
console.log(iterator.consumedCapacity);

ParallelScanIterator

Retrieves all pages of a DynamoDB scan utilizing a configurable number of scan segments that operate in parallel. When performing a parallel scan, you must specify the total number of segments you wish to use, and neither an ExclusiveStartKey nor a Segment identifier may be included with the input provided.

Example usage

import { ParallelScanIterator} from '@aws/dynamodb-query-iterator';
import DynamoDB = require('aws-sdk/clients/dynamodb');

const iterator = new ParallelScanIterator(
    new DynamoDB({region: 'us-west-2'}),
    {
        TableName: 'my_table',
        TotalSegments: 4,
        ReturnConsumedCapacity: 'INDEXES'
    },
    ['partitionKey']
);

for await (const record of iterator) {
    // do something with `record`
}

// Inspect the total number of items yielded
console.log(iterator.count);

// Inspect the total number of items scanned by this operation
console.log(iterator.scannedCount);

// Inspect the capacity consumed by this operation 
// This will only be available if `ReturnConsumedCapacity` was set on the input
console.log(iterator.consumedCapacity);

If you find any bugs or have a feature request, please open an issue on github!

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