Remote-Collection

A TypeScript RemoteData Collection class

---

There have been a number of articles written about using Algebraic Data Types to describe the states that data fetching entails. Replacing isFetching and other patterns with explicit expressions of each state is helpful, but there is still room to improve on the developer experience of dealing with remote data in the real world. remote-collection aims to provide a user-friendly experience while keeping 100% type-safety.

A typical REST API lets you interface with remote Resources through well-known HTTP patterns. A User resource, for instance, might be accessible by making a GET https://api.myawesomeapp.com/user/some-id. You can update parts of that resource by making a PUT or PATCH request to that same URL, or creating a new resource at that URL by making a POST request.

A Collection is typically some ordered list of a Resource. You might have a Users collection, for instance. You can imagine that your API would support making a request to POST https://api.myawesomeapp.com/user with a well-formed User resource, and it would add that User resource to the Users collection. DELETE https://api.myawesomeapp.com/user/some-id would remove that User, etc.

One challenge with dealing with remote resources is identity of a resource within a collection. Typically, a resource would have an id field, or some other unique identifier that you use to tie a given resource to a collection. But, fetching a collection and then deleting one of the resources is a nested affair: The request to get the collection (GET /user), and the request to delete a resource (DELETE /user/some-id) both have states, data, failure cases to account for, etc.

remote-collection is here to help with that!

Views vs. Resources

The same set of resources might have different ordering, be a filtered set, or some other smaller subset of the overall set. We call these subsets "views". One of the requirements of a resource is that it is identifiable by some property. Typically an id, uri, href, or similar property. The set of those identified resources are normalized such that updates to that resource should be visible to other views that might include it.

The state of fetching the whole collection, and the state of each individual resource are possiblity divergent, so RemoteCollection stores those states separately. You may have a failure state in one of your resources, but are refetching the whole list, and RemoteCollection tracks both states.

Transitioning the RemoteData state

A helpful cheatsheet for how to transition to the different RemoteData states for views vs individual resources:

Remote State	View	Resource
RemoteInitial	reset	remove
RemotePending	refresh	fetch
RemoteFailure	withListFailure	withResourceFailure
RemoteRefresh	refresh	fetch
RemoteSuccess	withList	withResource

Usage

RemoteCollection (Constructor)

Creates a new RemoteCollection of a generic Resource type. It takes two arguments, the first being the key of the identifier on the resource.

Signature

RemoteCollection<Resource extends { [key: string]: any }>(
  idProp: keyof Resource
)

Examples

// Initialize a new empty RemoteCollection where the wrapped resource is a `User`
const collection = new RemoteCollection<User>('id');

Resource Methods

fetch

Sets the resource at the given ID to RemotePending, or if it is already a RemoteSuccess or RemoteRefresh, sets it to RemoteRefresh. Useful when making the initial call to the server to indicate that we're currently fetching this resource, or when updating or re-fetching a resource.

Signature

fetch(id: string): RemoteCollection<Resource>

Examples

const users: User[] = [{ id: 'a', name: 'Alice' }, { id: 'b', name: 'Bob' }];
const collection = new RemoteCollection<User>('id')
  .withList(users)
  .fetch('a')
  .fetch('c');
  
assert.deepStrictEqual(
  collection.find('a'),
  RemoteData.refresh({ id: 'a', name: 'Alice' })
);

assert.deepStrictEqual(
  collection.find('c'),
  RemoteData.pending
);

withResource

Add or update a single Resource. Does not add resource to any views, but does update the resource based on the idProp, so if any views are listing that resource, they will see the update.

If you're trying to add a single resource to a view, you should use concat.

Signature

withResource(
  resource: Resource
): RemoteCollection<Resource>

Example

const collection = new RemoteCollection<User>('id');

assert.deepStrictEqual(
  collection.withResource(users[0]).find(users[0].id),
  RemoteData.success(users[0])
);

assert.deepStrictEqual(
  collection.withResource(users[0]).view(),
  RemoteData.initial
);

assert.deepStrictEqual(
  collection.withResource(users[0]).view('team1'),
  RemoteData.initial
);

assert.deepStrictEqual(
  collection.withList(users).withResource({ id: 'a', name: 'Alison' }).view(),
  RemoteData.success([{ id: 'a', name: 'Alison' }, { id: 'b', name: 'Bob' }])
);

withResourceFailure

If requesting a single resource fails, calling this method will store a RemoteFailure with the passed string in the resource map for just this resource.

Signature

withResourceFailure(id: string, error: string): RemoteCollection<Resource>

find

Lookup a resource by its idProp. NOTE: If the resource has never been requested, or has been removed, we return RemoteInitial indicating that is has not been retrieved.

Signature

find(id: string): RemoteData<string[], Resource>

Example

const collection = new RemoteCollection<User>('id');

assert.deepStrictEqual(
  collection.find('a'),
  RemoteData.initial
);

assert.deepStrictEqual(
  collection.withResource({ id: 'a', name: 'Alice' }).find('a'),
  RemoteData.success({ id: 'a', name: 'Alice' })
);

assert.deepStrictEqual(
  collection.withResourceFailure('b', 'Not authorized').find('b'),
  RemoteData.failure(['Not authorized'])
);

remove

Removes the resource indicated by the id.

Signature

remove(id: string): RemoteCollection<Resource>

Examples

const users: User[] = [{ id: 'a', name: 'Alice' }, { id: 'b', name: 'Bob' }];
const collection = new RemoteCollection<User>('id').withList(users);
  
assert.deepStrictEqual(
  collection.view(),
  RemoteData.success(users)
);

assert.deepStrictEqual(
  collection.remove('a').view(),
  RemoteData.success([users[1]])
);

Collection Methods

refresh

Like fetch but for the whole list. The optional at arguments allows you to specify the view key to refresh.

Signature

refresh(viewKey?: string = RemoteCollection.DEFAULT_KEY): RemoteCollection<Resource>

Examples

const users: User[] = [{ id: 'a', name: 'Alice' }, { id: 'b', name: 'Bob' }];
const collection = new RemoteCollection<User>('id');

assert.deepStrictEqual(
  collection.refresh().view(),
  RemoteData.pending
);
  
assert.deepStrictEqual(
  collection.withList(users).refresh().view(),
  RemoteData.refresh(users)
);
  
assert.deepStrictEqual(
  collection.withList(users, 'team1').refresh('team1').view(),
  RemoteData.refresh(users)
);

withList

Set or replace the list of resources.

This method adds a list of resources to the RemoteCollection representing the normal success-case for fetching the collection at the view key specified by the second argument, or RemoteCollection.DEFAULT_KEY if not provided.

Signature

withList(
  list: Resource[],
  viewKey?: string = RemoteCollection.DEFAULT_KEY
): RemoteCollection<Resource>

Example

const collection = new RemoteCollection<User>('id');

assert.deepStrictEqual(
  collection.withList(users).view(),
  RemoteData.success(users)
);

assert.deepStrictEqual(
  collection.withList(users).view(),
  collection.withList(users).view(RemoteCollection.DEFAULT_KEY)
);

assert.deepStrictEqual(
  collection.withList(users, 'team1').view('team1'),
  RemoteData.success(users)
);

withListFailure

If requesting the list fails, calling this method will store a RemoteFailure with the passed string at the view key specified by the second argument, or RemoteCollection.DEFAULT_KEY if not provided.

Signature

withListFailure(
  error: string,
  viewKey?: string = RemoteCollection.DEFAULT_KEY
): Collection<Resource>

view

Return the list of resources at a view key, or default to RemoteCollection.DEFAULT_KEY if none is provided.

Signature

public view(viewKey?: string = RemoteCollection.DEFAULT_KEY): RemoteData<string[], Resource[]>

Examples

Here is a break down of what to expect:

• If the list was successfully retrieved, and all resources corresponding to the IDs in that list are successful (meaning they haven't later been updated to other RemoteData states), you will receive a RemoteSuccess containing a list of all of the resources.

  const users: User[] = [{ id: 'a', name: 'Alice' }, { id: 'b', name: 'Bob' }];
  const collection = new RemoteCollection<User>('id').withList(users);
  assert.deepStrictEqual(collection.view(), RemoteData.success(users));

• If there was a failure when retrieving the list, you will receive the RemoteFailure with the failure string.

  const collection = new RemoteCollection<User>()
    .withListFailure('Not authorized');
  assert.deepStrictEqual(
    collection.view(),
    RemoteData.failure(['Not authorized'])
  );

• If retrieving the list succeeded, but later some subset of the resources had a failure, you will receive all of the failure strings in the RemoteFailure.

  const users: User[] = [
    { id: 'a', name: 'Alice' },
    { id: 'b', name: 'Bob' },
    { id: 'c', name: 'Charlie' }
  ];
  const collection = new RemoteCollection<User>('id')
    .withList(users)
    .withResourceFailure('a', 'Bad request')
    .withResourceFailure('c', 'Conflict');
  
  assert.deepStrictEqual(
    collection.view(),
    RemoteData.failure(['Bad request', 'Conflict'])
  );

• If the list, or any resource, is RemoteInitial or RemotePending, you will receive that value, even if some of them are RemoteFailure, RemoteSuccess, or RemoteRefresh.

  const users: User[] = [
    { id: 'a', name: 'Alice' },
    { id: 'b', name: 'Bob' },
    { id: 'c', name: 'Charlie' }
  ];
  const collection = new RemoteCollection<User>('id')
    .withList(users)
    .fetch('d');
  
  assert.deepStrictEqual(
    collection.view(),
    RemoteData.pending
  );

Using a view key:

const collection = new RemoteCollection<User>('id')
  .withList(users, 'team1');
  
assert.deepStrictEqual(
  collection.view(),
  RemoteData.initial
);

assert.deepStrictEqual(
  collection.view('team1'),
  RemoteData.success(users);
);

concat

Appends a RemoteCollection to another. The source's views are added to the end of the instance's existing views. The resources in the source overwrite any sources with matching idProp in the instance, and new resources are added.

Signature

concat(
  source: RemoteCollection<Resource>
): RemoteCollection<Resource>

Example

Adding resources to the beginning of a view

const users: User[] = [
  { id: 'a', name: 'Alice' },
  { id: 'b', name: 'Bob' }
];
const otherUsers: User[] =[
  { id: 'c', name: 'Charlie' }
];
const existing = new RemoteCollection<User>('id').withList(otherUsers, 'team1');
const collection = new RemoteCollection<User>('id').withList(users, 'team1');

assert.deepStrictEqual(
  collection.concat(existing).view('team1'),
  RemoteData.success([
    { id: 'a', name: 'Alice' },
    { id: 'b', name: 'Bob' },
    { id: 'c', name: 'Charlie' }
  ])
);

Adding a single resource to a view

const users = [{ id: 'a', name: 'Alice' }, { id: 'b', name: 'Bob' }];
const newUser = { id: 'd', name: 'Derrick' };
const collection = new RemoteCollection<User>('id').withList(users, 'team1');
const withNewUser = new RemoteCollection<User>().withList([newUser], 'team1')

assert.deepStrictEqual(
  collection.concat(withNewUser).view('team1'),
  RemoteData.success([
    { id: 'a', name: 'Alice' },
    { id: 'b', name: 'Bob' },
    { id: 'd', name: 'Derrick' }
  ])
);

union

Unites a RemoteCollection to another. The source's views are added to the end of the instance's existing views. If an item already exists in the source's view, it is not appended, such that the item stays in the same place as it did in the source's view. The resources in the source overwrite any sources with matching idProp in the instance, and new resources are added.

Signature

union(
  source: RemoteCollection<Resource>
): RemoteCollection<Resource>

Example

Adding some items without adding duplicates

const users: User[] = [
  { id: 'a', name: 'Alice' },
  { id: 'b', name: 'Bob' }
];
const otherUsers: User[] =[
  { id: 'a', name: 'Alex' },
  { id: 'c', name: 'Charlie' }
];
const collection = new RemoteCollection<User>('id').withList(users, 'team1');
const updated = new RemoteCollection<User>('id').withList(otherUsers, 'team1');

assert.deepStrictEqual(
  collection.union(updated).view('team1'),
  RemoteData.success([
    { id: 'a', name: 'Alex' },
    { id: 'b', name: 'Bob' },
    { id: 'c', name: 'Charlie' }
  ])
);

map

Apply a function to every resource at a view key. Note: Be careful if your function updates the property at the idProp, since that could invalidate the key that is storing the resource.

Signature

map(
  fn: (resource: Resource, index: string) => Resource,
  viewKey?: string = RemoteCollection.DEFAULT_KEY
): RemoteCollection<Resource>

Example

const users: User[] = [
  { id: 'a', name: 'Alice' },
  { id: 'b', name: 'Bob' }
];
const collection = new RemoteCollection<User>('id').withList(users, 'team1');

assert.deepStrictEqual(
  collection.map(u => ({ ...u, name: u.name.toUpperCase() }), 'team1'),
  RemoteData.success([
    { id: 'a', name: 'ALICE' },
    { id: 'b', name: 'BOB' }
  ])
);

omit

Signature

omit(id: string, viewKey?: string = RemoteCollection.DEFAULT_KEY): RemoteCollection<Resource>

Example

const collection = new RemoteCollection<User>('id').withList(users, 'team1');

assert.deepStrictEqual(
  collection.view('team1'),
  RemoteData.success(users)
);

assert.deepStrictEqual(
  collection.omit('a', 'team1').view('team1'),
  RemoteData.success([{ id: 'b', name: 'Bob' }])
);

reset

Removes the view at the given view key, or at the RemoteCollection.DEFAULT_KEY.

Signature

reset(viewKey?: string = RemoteCollection.DEFAULT_KEY): RemoteCollection<Resource>

Example

const collection = new RemoteCollection<User>('id').withList(users, 'team1');

assert.deepStrictEqual(
  collection.view('team1'),
  RemoteData.success(users)
);

assert.deepStrictEqual(
  collection.reset('team1').view('team1'),
  RemoteData.initial
);