Prisma Client isn't generated on deploying to Vercel

Bug description

As per the following discussion:

https://github.com/prisma/prisma/discussions/5140

How to reproduce

Deploying prisma to Vercel breaks

So I’ve started my project from the official example found here. This project works perfectly when deployed to Vercel directly because it forces Vercel to download, build and generate the prisma client.

Unfortunately, if you were to upload your project to Github and set up auto-deploys on commit, you will soon find a bunch of errors related to @prisma/client missing exports in your build outputs. For me these were missing types for my data and even native exports like empty and sql.

If you were to try to access your API you would most likely be able to see something like 2021-01-17T16:41:33.659Z undefined ERROR Error: You most likely forgot to initialize the Prisma Client. Please run prisma generate and try to run it again. in your function logs.

Why this happens

Vercel, like many other serverless hosts, uses a package-lock-based cache. What this means in practice is:

1. Change is made to the Github
2. Vercel sees the changes
3. Checks if anything has changed in package-lock
4. If it’s the same as the previous commit, it downloads a cache of node_modules

Unfortunately, node_modules is where the prisma client (which contains all of our types) is kept. And even more unfortunately, changes to our API which would be reflected in our types when running npm run generate does not make changes to package-lock.

In short this means that even though our app may have gone through significant changes, if package-lock isn’t deleted manually, our types will not be generated, which in turn will most likely break our API.

Expected behavior

A workaround should be possible to generate the PrismaClient in Vercel.

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I was able to reproduce this problem and solve it by adding the postinstall: prisma generate to package.json.

This was confirmed by the Vercel team who clarified that:

Having prisma generate as the postinstall command is a way to ensure that is always run after the initial build step, regardless of whether it used the cached node_modules or not.

From my tests, it seems that the trick that we do when building on Vercel, doesn’t always actually work (CC: @timsuchanek).

@creativiii I’d suggest you add the postinstall script and see if that solves the problem for you.

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Closing this issue as it was due to misconfiguration.

If you encounter this error, ensure that you have prisma generate in the postinstall hook. This is because the postinstall hook runs after the node_modules is loaded from cache on Vercel.