This package provides helpful TypeScript utilities for interacting with a DynamoDB table and maintaining complete type safety.

Installation

yarn add @lifeomic/dynamost @aws-sdk/client-dynamodb @aws-sdk/lib-dynamodb

Usage

First, declare a schema for your table using zod. This schema can be arbitarily complex, but it must reflect a JSON-serializable object.

const MySchema = z.object({
  id: z.string(),
  name: z.string(),
  createdAt: z.string().datetime(),
  deletable: z.boolean().optional(),
});

Next, create a DynamoTable instance using the schema and the configuration of the table in DynamoDB.

import { DynamoDBClient } from '@aws-sdk/client-dynamodb';
import { DynamoDBDocument } from '@aws-sdk/lib-dynamodb';

import { DynamoTable } from '@lifeomic/dynamost';

const table = new DynamoTable(
  // Provide a Document client.
  DynamoDBDocument.from(new DynamoDBClient({})),
  // Specify your Schema.
  MySchema,
  // Specify the table configuration.
  {
    // Specify the table name,
    tableName: 'my-table',
    // Specify the key schema for the table.
    keys: { hash: 'id', range: undefined },
    // Specify any secondary indexes.
    secondaryIndexes: {
      'name-index': { hash: 'name', range: 'createdAt' },
    },
  },
);

Now, you can begin interacting with the table.

await table.put({
  id: '123',
  name: 'First Item',
  createdAt: new Date().toISOString(),
});

await table.get({ id: '123' });

await table.queryIndex('name-index', { id: '123' });

For details on the available methods, see the API reference.

Conditions and Expressions

Wherever conditions or expressions are supported in the API, Dynamost uses a custom expression syntax that allows for type safety and maximizes readability.

For more details, see:

• Update Expression Syntax
• Condition Expression Syntax

API Reference

DynamoTable

put

Creates an item in the table.

const result = await table.put({
  id: '123',
  name: 'First Item',
  createdAt: new Date().toISOString(),
});

By default, put will not overwrite existing items, and will throw a ConditionCheckFailedException if the specified item already exists in the table. If you want to overwrite existing items, you can use the overwrite option:

const result = await table.put(
  {
    id: '123',
    name: 'First Item',
    createdAt: new Date().toISOString(),
  },
  { overwrite: true },
);

put also accepts an optional condition parameter that can be used to assert a condition:

const result = await table.put(
  {
    id: '123',
    name: 'First Item',
    createdAt: new Date().toISOString(),
  },
  {
    overwrite: true,
    condition: {
      equals: { name: 'First Item' },
    },
  },
);

get

Retrieves an item in the table by its key. Returns undefined if the item does not exist.

const result = await table.get({ id: '123' });

To perform a consistent read, use the consistentRead option:

const result = await table.get({ id: '123' }, { consistentRead: true });

delete

Deletes an item in the table by its key.

await table.delete({ id: '123' });

delete is idempotent by default, and will not throw an error if the item does not exist.

delete accepts an optional condition parameter that can be used to assert a condition:

await table.delete(
  { id: '123' },
  {
    condition: {
      equals: { name: 'First Item' },
    },
  },
);

query

Performs a query against the table. To query an index, use queryIndex

const result = await table.query({ id: '123' });

// The list of items returned by the query.
result.items;
// An opaque token that can be used to retrieve the next page of results.
result.nextPageToken;

If the table is configured with a range key, you can specify a key condition for the range key:

await table.query({
  id: '123',
  createdAt: {
    'greater-than': new Date().toISOString(),
  },
});

query accepts a number of options:

const result = await table.query(
  { id: '123' },
  {
    /** The maximum number of records to retrieve. */
    limit: 100,
    /** Whether to scan the index in ascending order. Defaults to `true`. */
    scanIndexForward: false,
    /**
     * A page token from a previous query. If provided, the query will
     * resume from where the previous query left off.
     */
    nextPageToken: '...',
    /**
     * Whether to perform a consistent query. Only valid when querying
     * the main table.
     */
    consistentRead: true,
  },
);

queryIndex

Performs a query against a secondary index.

const result = await table.queryIndex('name-index', { name: 'First Item' });

// The list of items returned by the query.
result.items;
// An opaque token that can be used to retrieve the next page of results.
result.nextPageToken;

queryIndex accepts the same options as query.

patch

Applies a "patch" to a single record in the table.

For more details on the syntax of patches, see Update Expression Syntax.

const updated = await table.patch(
  // The key of the item to patch.
  { id: '123' },
  // An update expression.
  { set: { name: 'Updated Item' } },
);

If the item does not exist, patch will throw a ConditionCheckFailedException.

patch also accepts an optional condition parameter that can be used to assert a condition:

const result = await table.patch(
  { id: '123' },
  { set: { name: 'Updated Item' } },
  {
    condition: {
      equals: { name: 'First Item' },
    },
  },
);

upsert

Modifies (or creates) an item using optimistic locking.

const updated = await table.upsert(
  // The key of the item to patch.
  { id: '123' },
  // A modification function that returns the desired new state of the item.
  (existing) => {
    if (!existing) {
      throw new Error('Item does not exist');
    }
    return { ...existing, name: 'Updated Item' };
  },
);

"Locking" Strategy

upsert implements an "optimistic lock" against the entire item. So:

If the modification function is called with undefined, then:

• The item did not exist at read-time, and
• The returned "new state" of the item will only be applied if the item still does not exist at write-time.

Otherwise, if the modification function is called with an existing item, then:

• The item did exist and read-time, and
• The returned "new state" of the item will only be applied if all of existing item's attributes are the same at write-time.

Important

• The locking strategy does not prevent writes in the case of a new attribute being added to an item during the course of a modification.

• upsert will automatically retry if it encounters a condition check failure. Retries will re-fetch the existing item, and re-run the modification function. If the maximum number of retries is exceeded, upsert will re-throw the final ConditionCheckFailedException.

• By default, any errors thrown during the modification function will not trigger retries, and will be immediately re-thrown by upsert. In order to throw an error that will trigger retries, use the retry function:

  await table.upsert({ id: '123' }, (existing, retry) => {
    if (existing.name !== 'First Item') {
      return retry('Item does not have expected name yet');
    }
    return { ...existing, name: 'Updated Item' };
  });

batchPut

Puts multiple items to the table.

await table.batchPut([
  {
    id: '123',
    name: 'First Item',
    createdAt: new Date().toISOString(),
  },
  {
    id: '124',
    name: 'Second Item',
    createdAt: new Date().toISOString(),
  },
  {
    id: '125',
    name: 'Third Item',
    createdAt: new Date().toISOString(),
  },
]);

batchDelete

Deletes the specified items from the table.

await table.batchDelete([{ id: '123' }, { id: '124' }, { id: '125' }]);

deleteAll

Deletes all items that match the specified query. Generally accepts the same parameters as query.

To delete against an index, use deleteAllForIndex

await table.deleteAll({ id: '123' });

deleteAllForIndex

Deletes all items that match the specified index query. Generally accepts the same parameters as queryIndex.

await table.deleteAllForIndex('name-index', { name: 'First Item' });

Update Expression Syntax

set

// Sets the "name" attribute to "Updated Item"
const update = {
  set: {
    name: 'Updated Item',
  },
};
// Sets the "name" attribute to "Updated Item"
// AND
// Sets the "deletable" attribute to `true`
const update = {
  set: {
    name: 'Updated Item',
    deletable: true,
  },
};

Condition Expression Syntax

Condition Expression Operators

The following expression operators are supported:

attribute-exists

// Asserts that the item has a "deletable" attribute.
const condition = {
  'attribute-exists': ['deletable'],
};

attribute-not-exists

// Asserts that the item does _not_ have a "deletable" attribute.
const condition = {
  'attribute-not-exists': ['deletable'],
};

equals

// Asserts that the item has a "name" attribute with the value "First Item".
const condition = {
  equals: {
    name: 'First Item',
  },
};

not-equals

// Asserts that the item does not have a "name" attribute with the value "First Item".
const condition = {
  'not-equals': {
    name: 'First Item',
  },
};

between

// Asserts that the item's "createdAt" value is between the two values.
const condition = {
  between: {
    createdAt: [
      new Date('2020-01-01').toISOString(),
      new Date('2020-01-02').toISOString(),
    ],
  },
};

begins-with

// Asserts that the item's "createdAt" value begins with "2020-01-01".
const condition = {
  'begins-with': {
    createdAt: '2020-01-01',
  },
};

greater-than

// Asserts that the item's "createdAt" value is greater than "2020-01-01".
const condition = {
  'greater-than': {
    createdAt: '2020-01-01',
  },
};

greater-than-or-equal-to

// Asserts that the item's "createdAt" value is greater than or equal to "2020-01-01".
const condition = {
  'greater-than-or-equal-to': {
    createdAt: '2020-01-01',
  },
};

less-than

// Asserts that the item's "createdAt" value is less than "2020-01-01".
const condition = {
  'less-than': {
    createdAt: '2020-01-01',
  },
};

less-than-or-equal-to

// Asserts that the item's "createdAt" value is less than or equal to "2020-01-01".
const condition = {
  'less-than-or-equal-to': {
    createdAt: '2020-01-01',
  },
};

Composing Conditions

Conditions can be composed in a handful of ways.

and

// Asserts that:
// - the item has a "name" attribute with the value "First Item".
// AND
// - the item has a "deletable" attribute.
const condition = {
  and: [
    { equals: { name: 'First Item' } },
    { 'attribute-exists': ['deletable'] },
  ],
};

Using multiple entries in a single condition operator is equivalent to using and.

// Asserts that:
// - the item has a "name" attribute with the value "First Item".
// AND
// - the item has a "deletable" attribute with the value `true`
const condition = {
  equals: {
    name: 'First Item',
    deletable: true,
  },
};

or

// Asserts that:
// - the item has a "name" attribute with the value "First Item".
// OR
// - the item has a "deletable" attribute.
const condition = {
  or: [
    { equals: { name: 'First Item' } },
    { 'attribute-exists': ['deletable'] },
  ],
};

Transactions

Transactions are supported via the TransactionManager class, which is nicely integrated with the methods that the DynamoTable exposes.

Usage

import { DynamoDBClient } from '@aws-sdk/client-dynamodb';
import { DynamoDBDocument } from '@aws-sdk/lib-dynamodb';
import { DynamoTable } from '@lifeomic/dynamost';

const client = new DynamoDBClient({});
const tableClient  = DynamoDBDocument.from(client)

const userTable = new DynamoTable(tableClient, /* user table definition */);
const membershipTable = new DynamoTable(tableClient, /* membership table definition */);
const transactionManager = new TransactionManager(client);

// Run any custom logic that requires a transaction inside the callback passed
// to "transactionManager.run". This was inspired by the sequelize transaction
// API. The callback (i.e. the transaction runner) should be synchronous. The
// reason for this is so that the compiler can catch incorrect uses of
// non-transactional methods.
await transactionManager.run((transaction) => {
  // Write any custom logic here. Leverage transactional writes by passing in
  // the transaction object to any of the DynamoTable methods that accept it.

  const newUser = { id: 'user-1', name: 'John Doe' };
  // This won't actually commit the write at this point. It'll gather all writes
  // and execute all the callback's logic first. After that, it will try to
  // commit all the write transactions at once.
  userTable.putTransact(newUser, { transaction });

  userTable.patchTransact(
    { id: 'user-2' },
    { set: { name: 'John Snow' } },
    {
      condition: {
        equals: { name: 'John S.' },
      },
      transaction,
    },
  );

  const newMembership = { userId: 'user-1', type: 'basic' };
  // You can use multiple tables when executing a transaction.
  membershipTable.putTransact(newMembership, { transaction });

  // Some more custom logic, it can be anything as long as it's synchronous.
});

Limitations

The TransactionManager currently only supports write transactions. More specifically, DynamoTable only supports the following methods when used in conjuction with the TransactionManager:

• putTransact
• patchTransact
• deleteTransact