Amazon DynamoDB DataMapper

This library provides a DataMapper class that allows easy interoperability between your application's domain classes and their persisted form in Amazon DynamoDB. Powered by the @block65/dynamodb-data-marshaller and @block65/dynamodb-expressions packages, using DataMapper lets you define each object's persisted representation once and then load, save, scan, and query your tables using the vocabulary of your application domain rather than its representation in DynamoDB.

Getting started

To use the DataMapper with a given JavaScript class, you will need to add a couple properties to the prototype of the class you would like to map to a DynamoDB table. Specifically, you will need to provide a schema and the name of the table:

import {DynamoDbSchema, DynamoDbTable} from '@block65/dynamodb-data-mapper';

class MyDomainModel {
    // declare methods and properties as normal
}

Object.defineProperties(MyDomainModel.prototype, {
    [DynamoDbTable]: {
        value: 'MyTable'
    },
    [DynamoDbSchema]: {
        value: {
            id: {
                type: 'String',
                keyType: 'HASH'
            },
            foo: {type: 'String'},
            bar: {
                type: 'Set',
                memberType: 'String',
            },
            baz: {
                type: 'Tuple',
                members: [
                    {type: 'Boolean'},
                    {type: 'String'},
                ],
            },
        },
    },
});

The schema and table name may be declared as property accessors directly on the class if the value should be determined dynamically:

import {DynamoDbTable} from '@block65/dynamodb-data-mapper';

class MyOtherDomainClass {
    id: number;

    get [DynamoDbTable]() {
        return this.id % 2 === 0 ? 'evens' : 'odds';
    }
}

Next, create an instance of DataMapper and use the MyDomainClass constructor defined above to save and load objects from DynamoDB:

import {
    DataMapper,
    DynamoDbSchema,
    DynamoDbTable,
} from '@block65/dynamodb-data-mapper';
import DynamoDB = require('aws-sdk/clients/dynamodb');

const client = new DynamoDB({region: 'us-west-2'});
const mapper = new DataMapper({client});

class MyDomainModel {
    id: string;
    foo?: string;
    bar?: Set<string>;
    baz?: [boolean, string];
}

Object.defineProperties(MyDomainModel.prototype, {
    [DynamoDbTable]: {
        value: 'MyTable'
    },
    [DynamoDbSchema]: {
        value: {
            id: {
                type: 'String',
                keyType: 'HASH'
            },
            foo: {type: 'String'},
            bar: {
                type: 'Set',
                memberType: 'String',
            },
            baz: {
                type: 'Tuple',
                members: [
                    {type: 'Boolean'},
                    {type: 'String'},
                ],
            },
        },
    },
});

// delete an object
const toDelete = new MyDomainModel();
toDelete.id = 'DELETE_ME';
mapper.delete(toDelete);

// if that's too verbose, you can write the above as a single expression with
// Object.assign:
mapper.delete(Object.assign(new MyDomainModel(), {id: 'DELETE_ME'}));

// fetch an object
const toGet = new MyDomainModel();
toGet.id = 'ID_TO_FETCH';
const fetched = await mapper.get(toGet);

// this should return a rejected promise, as it's fetching an object that does
// not exist
mapper.get(toDelete)
    .catch(err => console.log('I expected this to happen'));

// put something new into the database
const toPut = new MyDomainModel();
toPut.id = 'NEW_RECORD';
toPut.foo = 'bar';
toPut.bar = new Set<string>(['fizz', 'buzz', 'pop']);
toPut.baz = [true, 'quux'];

mapper.put(toPut).then((persisted: MyDomainModel) => {
    // now change the record a bit
    const toUpdate = new MyDomainModel();
    toUpdate.id = persisted.id;
    toUpdate.baz = [false, 'beep'];
    return mapper.update(toUpdate, {onMissing: 'skip'});
});

Supported operations

batchDelete

Deletes any number of items from one or more tables in batches of 25 or fewer items. Unprocessed deletes are retried following an exponentially increasing backoff delay that is applied on a per-table basis.

Returns an async iterable of items that have been deleted (deleted items are yielded when the delete has been accepted by DynamoDB). The results can be consumed with a for-await-of loop. If you are using TypeScript, you will need to include esnext.asynciterable in your lib declaration (as well as enabling downlevelIteration if targeting ES5 or lower). Please refer to the TypeScript release notes for more information.

Takes one parameter:

• An iterable (synchronous or asynchronous) of items to delete. Each item must be an instance of a class with a table name accessible via a property identified with the DynamoDbTable symbol and a schema accessible via a property identified with the DynamoDbSchema symbol.

batchGet

Fetches any number of items from one or more tables in batches of 100 or fewer items. Unprocessed reads are retried following an exponentially increasing backoff delay that is applied on a per-table basis.

Takes two parameters:

• An iterable (synchronous or asynchronous) of items to fetch. Each item must be an instance of a class with a table name accessible via a property identified with the DynamoDbTable symbol and a schema accessible via a property identified with the DynamoDbSchema symbol.

• (Optional) An object specifying any of the following options:

  • readConsistency - Specify 'strong' to perform a strongly consistent read. Specify 'eventual' (the default) to perform an eventually consistent read.

  • perTableOptions - An object whose keys are table names and whose values are objects specifying any of the following options:

    • readConsistency - Specify 'strong' to perform a strongly consistent read. Specify 'eventual' (the default) to perform an eventually consistent read.

    • projection - A projection expression directing DynamoDB to return a subset of the fetched item's attributes. Please refer to the documentation for the @block65/dynamodb-expressions package for guidance on creating projection expression objects.

    • projectionSchema - The schema to use when mapping the supplied projection option to the attribute names used in DynamoDB.

      This parameter is only necessary if a batch contains items from multiple classes that map to the same table using different property names to represent the same DynamoDB attributes.

      If not supplied, the schema associated with the first item associated with a given table will be used in its place.

batchPut

Puts any number of items to one or more tables in batches of 25 or fewer items. Unprocessed puts are retried following an exponentially increasing backoff delay that is applied on a per-table basis.

Returns an async iterable of items that have been put (put items are yielded when the put has been accepted by DynamoDB). The results can be consumed with a for-await-of loop. If you are using TypeScript, you will need to include esnext.asynciterable in your lib declaration (as well as enabling downlevelIteration if targeting ES5 or lower). Please refer to the TypeScript release notes for more information.

Takes one parameter:

• An iterable (synchronous or asynchronous) of items to put. Each item must be an instance of a class with a table name accessible via a property identified with the DynamoDbTable symbol and a schema accessible via a property identified with the DynamoDbSchema symbol.

batchWrite

Puts or deletes any number of items to one or more tables in batches of 25 or fewer items. Unprocessed writes are retried following an exponentially increasing backoff delay that is applied on a per-table basis.

Returns an async iterable of tuples of the string 'put'|'delete' and the item on which the specified write action was performed. The results can be consumed with a for-await-of loop. If you are using TypeScript, you will need to include esnext.asynciterable in your lib declaration (as well as enabling downlevelIteration if targeting ES5 or lower). Please refer to the TypeScript release notes for more information.

Takes one parameter:

• An iterable (synchronous or asynchronous) of tuples of the string 'put'|'delete' and the item on which to perform the specified write action. Each item must be an instance of a class with a table name accessible via a property identified with the DynamoDbTable symbol and a schema accessible via a property identified with the DynamoDbSchema symbol.

delete

Removes an item from a DynamoDB table. Takes two parameters:

• The item to be deleted. Must be an instance of a class with a table name accessible via a property identified with the DynamoDbTable symbol and a schema accessible via a property identified with the DynamoDbSchema symbol.

• (Optional) An object specifying any of the following options:

  • condition - A condition expression whose assertion must be satisfied in order for the delete operation to be executed. Please refer to the documentation for the @block65/dynamodb-expressions package for guidance on creating condition expression objects.

  • returnValues - Specify 'ALL_OLD' to have the deleted item returned to you when the delete operation completes.

  • skipVersionCheck - Whether to forgo creating a condition expression based on a defined versionAttribute in the schema.

get

Fetches an item from a DynamoDB table. If no item with the specified key was found, the returned promise will be rejected with an error. Takes two parameters:

• The item to be fetched. Must be an instance of a class with a table name accessible via a property identified with the DynamoDbTable symbol and a schema accessible via a property identified with the DynamoDbSchema symbol.

  The supplied item will NOT be updated in place. Rather, a new item of the same class with data from the DynamoDB table will be returned.

• (Optional) An object specifying any of the following options:

  • readConsistency - Specify 'strong' to perform a strongly consistent read. Specify 'eventual' (the default) to perform an eventually consistent read.

  • projection - A projection expression directing DynamoDB to return a subset of the fetched item's attributes. Please refer to the documentation for the @block65/dynamodb-expressions package for guidance on creating projection expression objects.

put

Inserts an item into a DynamoDB table. Takes two parameters:

• The item to be inserted. Must be an instance of a class with a table name accessible via a property identified with the DynamoDbTable symbol and a schema accessible via a property identified with the DynamoDbSchema symbol.

• (Optional) An object specifying any of the following options:

  • condition - A condition expression whose assertion must be satisfied in order for the put operation to be executed. Please refer to the documentation for the @block65/dynamodb-expressions package for guidance on creating condition expression objects.

  • returnValues - Specify 'ALL_OLD' to have the overwritten item (if one existed) returned to you when the put operation completes.

  • skipVersionCheck - Whether to forgo creating a condition expression based on a defined versionAttribute in the schema.

query

Retrieves multiple values from a table or index based on the primary key attributes. Queries must target a single partition key value but may read multiple items with different range keys.

This method is implemented as an async iterator and the results can be consumed with a for-await-of loop. If you are using TypeScript, you will need to include esnext.asynciterable in your lib declaration (as well as enabling downlevelIteration if targeting ES5 or lower). Please refer to the TypeScript release notes for more information.

Takes three parameters:

• The constructor function to use for any results returned by this operation. Must have a prototype with a table name accessible via a property identified with the DynamoDbTable symbol and a schema accessible via a property identified with the DynamoDbSchema symbol.

• The condition that specifies the key value(s) for items to be retrieved by the query operation. You may provide a hash matching key properties to the values they must equal, a hash matching keys to ConditionExpressionPredicates, or a fully composed ConditionExpression. If a hash is provided, it may contain a mixture of condition expression predicates and exact value matches:

  import {between} from '@block65/dynamodb-expressions';
  
  const keyCondition = {
      partitionKey: 'foo',
      rangeKey: between(10, 99),
  };

  The key condition must target a single value for the partition key.

  Please refer to the documentation for the @block65/dynamodb-expressions package for guidance on creating condition expression objects.

• (Optional) An object specifying any of the following options:

  • filter - A condition expression that DynamoDB applies after the Query operation, but before the data is returned to you. Items that do not satisfy the filter criteria are not returned.

    You cannot define a filter expression based on a partition key or a sort key.

    Please refer to the documentation for the @block65/dynamodb-expressions package for guidance on creating condition expression objects.

  • indexName - The name of the index against which to execute this query. If not specified, the query will be executed against the base table.

  • limit - The maximum number of items to return.

  • pageSize - The maximum number of items to return per page of results.

  • projection - A projection expression directing DynamoDB to return a subset of any fetched item's attributes. Please refer to the documentation for the @block65/dynamodb-expressions package for guidance on creating projection expression objects.

  • readConsistency - Specify 'strong' to perform a strongly consistent read. Specify 'eventual' (the default) to perform an eventually consistent read.

  • scanIndexForward - Specifies the order for index traversal: If true, the traversal is performed in ascending order; if false, the traversal is performed in descending order.

  • startKey - The primary key of the first item that this operation will evaluate.

Query metadata

The iterator returned by query will keep track of the number of items yielded and the number of items scanned via its count and scannedCount properties:

const iterator = mapper.query(
    MyClass, 
    {partitionKey: 'foo', rangeKey: between(0, 10)}
);
for await (const record of iterator) {
    console.log(record, iterator.count, iterator.scannedCount);
}

Pagination

If you wish to perform a resumable query, you can use the .pages() method of the iterator returned by query to access the underlying paginator. The paginator differs from the iterator in that it yields arrays of unmarshalled records and has a lastEvaluatedKey property that may be provided to a new call to mapper.query to resume the query later or in a separate process:

const paginator = mapper.query(
    MyClass,
    {partitionKey: 'foo', rangeKey: between(0, 10)},
    {
        // automatically stop after 25 items or the entire result set has been
        // fetched, whichever is smaller
        limit: 25
    }
).pages();

for await (const page of paginator) {
    console.log(
        paginator.count,
        paginator.scannedCount,
        paginator.lastEvaluatedKey
    );
}

const newPaginator = mapper.query(
    MyClass,
    {partitionKey: 'foo', rangeKey: between(0, 10)},
    {
        // start this new paginator where the previous one stopped
        startKey: paginator.lastEvaluatedKey
    }
).pages();

scan

Retrieves all values in a table or index.

This method is implemented as an async iterator and the results can be consumed with a for-await-of loop. If you are using TypeScript, you will need to include esnext.asynciterable in your lib declaration (as well as enabling downlevelIteration if targeting ES5 or lower). Please refer to the TypeScript release notes for more information.

Takes two parameters:

• The constructor function to use for any results returned by this operation. Must have a prototype with a table name accessible via a property identified with the DynamoDbTable symbol and a schema accessible via a property identified with the DynamoDbSchema symbol.

• (Optional) An object specifying any of the following options:

  • filter - A condition expression that DynamoDB applies after the scan operation, but before the data is returned to you. Items that do not satisfy the filter criteria are not returned.

    You cannot define a filter expression based on a partition key or a sort key.

    Please refer to the documentation for the @block65/dynamodb-expressions package for guidance on creating condition expression objects.

  • indexName - The name of the index against which to execute this query. If not specified, the query will be executed against the base table.

  • limit - The maximum number of items to return.

  • pageSize - The maximum number of items to return per page of results.

  • projection - A projection expression directing DynamoDB to return a subset of any fetched item's attributes. Please refer to the documentation for the @block65/dynamodb-expressions package for guidance on creating projection expression objects.

  • readConsistency - Specify 'strong' to perform a strongly consistent read. Specify 'eventual' (the default) to perform an eventually consistent read.

  • segment - The identifier for this segment (if this scan is being performed as part of a parallel scan operation).

  • startKey - The primary key of the first item that this operation will evaluate.

  • totalSegments - The number of segments into which this scan has been divided (if this scan is being performed as part of a parallel scan operation).

Scan metadata

The iterator returned by scan will keep track of the number of items yielded and the number of items scanned via its count and scannedCount properties:

const iterator = mapper.scan(MyClass);
for await (const record of iterator) {
    console.log(record, iterator.count, iterator.scannedCount);
}

Pagination

If you wish to perform a resumable scan, you can use the .pages() method of the iterator returned by scan to access the underlying paginator. The paginator differs from the iterator in that it yields arrays of unmarshalled records and has a lastEvaluatedKey property that may be provided to a new call to mapper.scan to resume the scan later or in a separate process:

const paginator = mapper.scan(
    MyClass,
    {
        // automatically stop after 25 items or the entire result set has been
        // fetched, whichever is smaller
        limit: 25
    }
).pages();
for await (const page of paginator) {
    console.log(
        paginator.count,
        paginator.scannedCount,
        paginator.lastEvaluatedKey
    );
}

const newPaginator = mapper.scan(
    MyClass,
    {
        // start this new paginator where the previous one stopped
        startKey: paginator.lastEvaluatedKey
    }
).pages();

parallelScan

Retrieves all values in a table by dividing the table into segments, all of which are scanned in parallel.

This method is implemented as an async iterator and the results can be consumed with a for-await-of loop. If you are using TypeScript, you will need to include esnext.asynciterable in your lib declaration (as well as enabling downlevelIteration if targeting ES5 or lower). Please refer to the TypeScript release notes for more information.

Takes three parameters:

• The constructor to use for any results returned by this operation. Must have a prototype with a table name accessible via a property identified with the DynamoDbTable symbol and a schema accessible via a property identified with the DynamoDbSchema symbol.

• The total number of parallel workers to use to scan the table.

• (Optional) An object specifying any of the following options:

  • filter - A condition expression that DynamoDB applies after the scan operation, but before the data is returned to you. Items that do not satisfy the filter criteria are not returned.

    You cannot define a filter expression based on a partition key or a sort key.

    Please refer to the documentation for the @block65/dynamodb-expressions package for guidance on creating condition expression objects.

  • indexName - The name of the index against which to execute this query. If not specified, the query will be executed against the base table.

  • pageSize - The maximum number of items to return per page of results.

  • projection - A projection expression directing DynamoDB to return a subset of any fetched item's attributes. Please refer to the documentation for the @block65/dynamodb-expressions package for guidance on creating projection expression objects.

  • readConsistency - Specify 'strong' to perform a strongly consistent read. Specify 'eventual' (the default) to perform an eventually consistent read.

  • startKey - The primary key of the first item that this operation will evaluate.

Scan metadata

The iterator returned by parallelScan will keep track of the number of items yielded and the number of items scanned via its count and scannedCount properties:

const iterator = mapper.parallelScan(MyClass, 4);
for await (const record of iterator) {
    console.log(record, iterator.count, iterator.scannedCount);
}

Pagination

If you wish to perform a resumable parallel scan, you can use the .pages() method of the iterator returned by parallelScan to access the underlying paginator. The paginator differs from the iterator in that it yields arrays of unmarshalled records and has a scanState property that may be provided to a new call to mapper.parallelScan to resume the scan later or in a separate process:

const paginator = mapper.parallelScan(
    MyClass,
    4
).pages();
for await (const page of paginator) {
    console.log(
        paginator.count,
        paginator.scannedCount,
        paginator.lastEvaluatedKey
    );

    break;
}

const newPaginator = mapper.parallelScan(
    MyClass,
    4,
    {
        // start this new paginator where the previous one stopped
        scanState: paginator.scanState
    }
).pages();

update

Updates an item in a DynamoDB table. Will leave attributes not defined in the schema in place.

Takes two parameters:

• The item with its desired property state. Must be an instance of a class with a table name accessible via a property identified with the DynamoDbTable symbol and a schema accessible via a property identified with the DynamoDbSchema symbol.

• (Optional) An object specifying any of the following options:

  • condition - A condition expression whose assertion must be satisfied in order for the update operation to be executed. Please refer to the documentation for the @block65/dynamodb-expressions package for guidance on creating condition expression objects.

  • onMissing - Specify 'remove' (the default) to treat the absence of a value in the supplied item as a directive to remove the property from the record in DynamoDB. Specify 'skip' to only update the properties that are defined in the supplied item.

  • skipVersionCheck - Whether to forgo creating a condition expression based on a defined versionAttribute in the schema.

executeUpdateExpression

Executes a custom update expression. This method will not automatically apply a version check, as the current state of the object being updated is not known.

Takes four parameters:

• The expression to execute. Please refer to the documentation for the @block65/dynamodb-expressions package for guidance on creating update expression objects.

• The key of the item being updated.

• The constructor for the class mapped to the table against which the expression should be run. Must have a prototype with a table name accessible via a property identified with the DynamoDbTable symbol and a schema accessible via a property identified with the DynamoDbSchema symbol.

• (Optional) An object specifying any of the following options:

  • condition - A condition expression whose assertion must be satisfied in order for the update operation to be executed. Please refer to the documentation for the @block65/dynamodb-expressions package for guidance on creating condition expression objects.