​
Usage

You can use the firestoreSet function to set a document at a specified path. The first argument is the slash-separated path of the collection containing the document. 
// Define a function to add a post
const setPost = firestoreSet('posts')

// Use the function to set a post
const postId = 'post-id-1'
await setPost(postId, { title: 'My updated post' })

​
Subcollections

Collections don’t have to be at the top level of the Firestore, adding slashes will set the document in a subcollection. For example, if you want to set a post in a collection of posts for a specific user: 
// Define a function to set a post
const postId = 'post-id-1'
const setComment = firestoreSet<Comment>(`posts/${postId}/comments`)

const commentId = 'comment-id-1'
const authorId = 'user-id-2'

await setComment(commentId, {
  body: 'On a second read, that was fantastic!',
  authorId,
})

​
Dynamic Paths

Using subcollections is a common pattern in Firestore since it makes writing security rules much easier. To make our function more reusable, we can use a function that takes an arguments object and returns a string representing the path: 
// Define a function to add a post
const setComment = firestoreSet<Comment>(
  ({ postId }) => `posts/${postId}/comments`,
)

const postId = 'post-id-1'
const commentId = 'comment-id-1'
const commentAuthorId = 'user-id-2'

await setComment(
  commentId,
  {
    body: 'On a second read, that was fantastic!',
    authorId: commentAuthorId,
  },
  { postId },
)
Even more convenient is to pull the postId from the comment itself, assuming the comment contains it. This can be done by using the data property of the arguments object which contains the data that will be written to the document: 
type Comment = {
  body: string
  postId: string
}

// Define a function to add a post
const setComment = firestoreSet<Post>(
  ({ data }) => `posts/${data.postId}/comments`,
)

const postId = 'post-id-1'
const commentId = 'comment-id-1'
const commentAuthorId = 'user-id-2'

await setComment(commentId, {
  body: 'On a second read, that was fantastic!',
  authorId: commentAuthorId,
  postId,
})

​
Return Value

The function returns a Promise that resolves with a DocumentReference to the newly created document. 
const ref = await setPost(postId, { title: 'My updated post' })

// The value returned is a DocumentReference
await ref.delete()

​
Type Safety

If a type parameter is provided, the returned function will be typesafe. It will allow any object of the provided type to be passed as the second argument. 
type Post = {
  title: string
  body: string
}

const setPost = firestoreSet<Post>('posts')

// This set will throw a type error since the post doesn't have a body.
await setPost(postId, { title: 'My updated post' })
The provided type definitions will help you to avoid common mistakes, but they are not realtime validation. You can still write invalid data to Firestore if you don’t use the provided functions correctly.

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Options

The second argument to firestoreSet is an optional object allowing for additional configuration. This object can have a property addMetadata which, if true, adds metadata to the document. 
// The setPost function will include metadata to the new document.
const setPost = firestoreSet<Post>('posts', { addMetadata: true })

await setPost('post_id_1', { title: 'First Post' })
await setPost('post_id_2', { title: 'Second Post' })
await setPost('post_id_3', { title: 'Third Post' })

// The posts will be ordered by the time they were created.
const recentPosts = await firestore
  .collection('posts')
  .orderBy('metadata.timeCreated', 'asc')
  .limit(10)
  .get()