dynaglue

v2.0.3

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2 months ago

dynaglue

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chris-armstrong

Dynaglue

dynaglue is an opinionated TypeScript/JavaScript library that makes single-table designs in DynamoDB easier to query and update.

npm install dynaglue

You also need to have the AWS SDK v3 for DynamoDB installed in your project (it is a peer dependency):

npm install @aws-sdk/client-dynamodb

Rationale

Querying and storing data in single-table DynamoDB designs is hard. Keeping indexes up-to-date and constructing DynamoDB queries and update expressions requires verbose code and that is easy to make mistakes and forget things.

dynaglue takes the hassle out of managing your data with a straightforward way to declare its mapping onto your table's indexes, and wraps it all up with simple and foolproof Mongo-like API.

See Motivation (below) for a more detailed explanation.

Benefits

Adds a rigorous model that makes it easy to implement numerous single-table patterns
Simple, Mongo-like interface to update and query your data
Easy to use query and filter expression syntax
Supports most of the DynamoDB functionality
Fully TypeScript-enabled API

Getting Started

A comprehensive Getting Started Guide is available explaining how to install and use dynaglue in a new project as well as all its current features (note it currently references the AWS v2 SDK - the current version requires AWS SDK v3).

See the examples directory for a more concise overview of its features in action.

Reference Documentation, generated from the source code, also contains useful information about the operations and types you need to use dynaglue.

Status

dynaglue is reasonably complete with a stable API. It is being improved over time and is used in production.

The current version uses AWS SDK v3, which is a peer-dependency.

There are some specific areas that could be improved, such as full transactions support, projection expressions, and returning capacity numbers.

Please try it out, report bugs, suggest improvements or submit a PR.

Usage Example

// Declare the layout of your table (its primary and secondary indexes and their key names)
const layout = {
  tableName: 'my-table',
  primaryKey: { partitionKey: 'id', sortKey: 'collection' },
  findKeys: [
    // 2 GSIs => up to 2 extra access patterns per collection
    { indexName: 'gs2', partitionKey: 'gs2p', sortKey: 'gs2s' },
    { indexName: 'gs3', partitionKey: 'gs3p', sortKey: 'gs3s' },
  ],
};

// Declare a collection for each data type (like a Mongo collection)
const usersCollection = {
  name: 'users',
  layout,
  // access patterns that are mapped to indexes in the table layout
  accessPatterns: [
    // 1. Find users by their email address on GSI2
    { indexName: 'gs2', partitionKeys: [], sortKeys: [['email']] },
    // 2. Find users by their team (and optionally, employee code)
    { indexName: 'gs3', partitionKeys: [['team', 'id']], sortKeys: [['team', 'employeeCode']] },
  ],
};
const ddb = new DynamoDBClient();
const ctx = createContext(ddb, [usersCollection]);

// Insert users into collection (auto-generated IDs)
const user1 = await insert(ctx, 'users', {
  name: 'Anayah Dyer',
  email: '[email protected]',
  team: { id: 'team-code-1', employeeCode: 'AC-1' },
});
const user2 = await insert(ctx, 'users', {
  name: 'Ruairidh Hughes',
  email: '[email protected]',
  team: { id: 'team-code-1', employeeCode: 'AC-2' },
});
const user3 = await insert(ctx, 'users', {
  name: 'Giles Major',
  email: '[email protected]',
  team: { id: 'team-code-2', employeeCode: 'GT-5' },
});
const user4 = await insert(ctx, 'users', {
  name: 'Lance Alles',
  email: '[email protected]',
  team: { id: 'team-code-2', employeeCode: 'GT-6' },
});

// Find a user by ID (uses primary index)
const foundUser = await findById(ctx, 'users', user2._id);
// => { _id: '...', name: 'Ruairidh Hughes', ... }

// Find a user by email (access pattern 1)
const userByEmail = await find(ctx, 'users', { email: '[email protected]' });
// => [{ _id: '...', name: 'Anayah Dyer', ... }]

// Find all users in a team (access pattern 2)
const usersInTeam2 = await find(ctx, 'users', { 'team.id': 'team-code-2' });
// => [{ _id: '...', name: 'Giles Major', ... }, { _id: '...', name: 'Lance Alles', ... }]

// Find user by teamId and employeeCode (access pattern 2)
const specificUser = await find(ctx, 'users', { 'team.id': 'team-code-1', employeeCode: 'AC-2' });
// => [{ _id: '...', name: 'Ruairidh Hughes', ... }]

// Update an item
const updatedItem = await updateById(ctx, 'users', user4._id, {
  'team.employeeCode': 'GT-10',
  'name': 'James Alles',
});

Prerequisite Knowledge

This library assumes you have a good understanding of DynamoDB basics and some understanding of single-table modelling.

If you need to get started, these are some good resources:

more advanced DynamoDB modelling, including single-table design:

and if you want to debate the usefulness of a single-table approach:

Debugging

You can see what it is doing to DynamoDB by running your code with the environment variable:

export DEBUG=dynaglue:*

which will print out the queries it executes.

Motivation

Apparently to use DynamoDB efficiently, you must:

purge yourself of any sensible knowledge of database design such as normalisation
know exactly how your application will access its data for now and into the future
pack multiple values into the same field in order to implement fast composite-key and hierarchical data lookups
mix multiple data structures together in the same table, distinguished only by prefixes and values

Once you've accepted all that is horrible as best practice, only then you may then build highly performant and scalable web applications.

The next stumbling block is DynamoDB's API: it does not make this easy. Combining multiple records from different data types sharing indexes in the same logical table requires discipline and attention to detail.

Most DynamoDB applications will attempt to avoid this by using separate tables for each type of data, using secondary indexes liberally and by naming their keys intuitively based on the data being modelled. This is actually fine: it makes working with the API less painful but it makes it harder to optimise for cost and performance.

This library is an attempt at a compromise - it presents a Mongo-like API for looking up data, but still relies on you to identify and declare your access patterns up front.

You can query your data as if your storage engine knows how to work out what index to use, but it will fail hard if it can't find that index, which is (counterintuitively) what you want with DynamoDB.

You can use it for single or multi-table designs (in reality, there is no such thing as single-table designs, because there will be at least one access pattern that is so different from your others that it would affect the performance of them if they shared an index or table).

Limitations

This is a list of current limitations:

Opinionated - the library follows popular practice on implementing a single-table design, but it makes some assumptions about how you want to store your data
No projection expression support
No support for projected indexes - all GSIs are assumed to project all the data. This library may support in the future splitting up your document so that you can use projected indexes to limit data in some indexes.
Only string types for values used to build indexes. Obviously numbers are also useful for sort key expressions, but they require more sophisticated handling than the library currently supports
Transaction Support is still in progress
No write sharding support for low-variance partition keys. (NOTE: This isn't important for most use cases) If you have hot partition keys with a small set of values e.g. status=(starting, started, stopping, stopped deleted) and you query them on one of those values relentlessly, you will get a hot partition. The normal solution is to add a suffix spread between a given set of values (e.g. 0-19) so that when it is queried on status the query can be split over 20 partitions instead of one.

Contributing

Open an Issue (especially before you write any code) and share your thoughts / plans / ideas before you do anything substantial.

Abuse, harassment, and anything else that is becoming unproductive will be closed without further engagement.

License

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.