While testing a site that used Prisma I had the need to clear the database from time to time, to clear the test data I entered.

You can clear items entered by using:

await prisma.user.deleteMany({})

If for some reason you want to iterate on the items to do some processing, you can iterate over them in this way:

const users = await prisma.user.findMany({})

const deleteUser = async (user) => {
  return await prisma.user.delete({
    where: { id: user.id }
  })
}

const deleteUsers = async () => {
  users.map((user) => deleteUser(user))
}

deleteUsers()

In this case I am not doing anything more than the previous example, which makes all this code redundant, but you could do anything you want inside deleteUser().

I had a problem though because I had a relation between 2 tables, tweets and users. A tweet was associated to a user. First I had to remove all tweets, then remove all users, so I wrote this function:

export const clearData = async (prisma) => {
  const users = await prisma.user.findMany({})
  const tweets = await prisma.tweet.findMany({})

  const deleteUser = async (user) => {
    return await prisma.user.delete({
      where: { id: user.id }
    })
  }
  const deleteTweet = async (tweet) => {
    return await prisma.tweet.delete({
      where: { id: tweet.id }
    })
  }

  const deleteTweets = async () => {
    return Promise.all(tweets.map((tweet) => deleteTweet(tweet)))
  }

  const deleteUsers = async () => {
    return Promise.all(users.map((user) => deleteUser(user)))
  }

  await deleteTweets()
  await deleteUsers()
}

Notice the use of Promise.all() to wrap users.map() so I could use await on it, so all tweets are removed before I start deleting users.

Lessons in this unit:

0:	Introduction
1:	How to use Prisma
2:	Prisma relations
3:	Using multiple fields for a unique key in Prisma
4:	Prisma, how to reverse order
5:	▶︎ Prisma, how to clear the database
6:	How to solve the `prisma/client did not initialize yet` error on Vercel