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Getting your Bearings as a Developer

Understand the Prisma and Nexus black magic

Prisma (without Nexus)

Prisma is an IDL-based ORM compiler. In simple terms, it works out of the prisma/schema.prisma file to provide your app with an object-oriented model of your SQL database.

To see it in action:

  1. Run npx prisma studio
  2. Edit ./schema/prisma.schema and perform a (relatively) small change, such as renaming a column (using @map("sqlColumnNameForThisField")) or table (@@map("sqlTableNameForThisModel")) Run npx prisma studio again to see your changes

💡 The prisma/schema.prisma is the pivot of your Prisma workflow: as a developer, you can either write that file by hand, or reverse-engineer it out of an existing database (npx prisma db pull). Thereafter, Prisma acts as the one-stop shop for all your SQL abstraction needs: multi-dialect OO mapping, Ruby-on-Rails-style schema migration and data seeding.

Nexus (and the two Prisma plug-ins)

Nexus is an opinionated GraphQL server built on top of Apollo. It lets you write the GraphQL schema (types, queries, mutations) in plain JavaScript (or TypeScript) instead of having to write them in the GraphQL language.

On top of that, nexus-plugin-prisma provides the magic that reads most of the GraphQL schema directly out of Prisma, without you having to type it in. As it turns out, there is a rewrite in progress for that plug-in, and for reasons that are covered in detail in the comments of ./nexus/schema.ts we have to use both the old and the new plug-ins.

To observe “simple” (run-time) Nexus in action:

  1. Run the test suite: 
    yarn test
    A green bar is expected, otherwise see in README.md regarding setting up the ssh tunnel
  2. Open ./schema/rooms.ts to take a look at what Nexus-style definitions for GraphQL types and queries look like
  3. Remove Room.building from the fields list next to definition(t) and run the test suite again with debugging on: 
    DEBUG=lhd-tests:'*' yarn test
    You should now be getting GraphQL errors with messages like Cannot query field "building" on type "Room"
  4. Don't forget to revert the change before moving on

💡 In the ./schema/rooms.ts file we can see both the “new” Prisma plug-in in action (the line that imports from 'nexus-prisma') and the “old” one which is behind t.crud, which automagically takes care of querying, filtering and more for us.

Generated typings in Nexus and Prisma

... But wait, there is more to Nexus and Prisma.

  1. Fire up an IDE that understands TypeScript, such as Visual Studio Code or IntelliJ
  2. Create a new file foo.ts anywhere and start typing
    import { Room } from '@prisma/client'
    You will get a warning regarding Room being unused (which you can fix by replacing import with export, if you like), but no errors
  3. Replace Room with something that doesn't exist, e.g. Roomzor. Now an error appears!

There is black magic at play here: the types of @prisma/client aren't limited to just what came out of the @prisma/client NPM download. Rather, a build-time procedure (that you can run manually with yarn codegen; see package.json) creates additional TypeScript typings (and actually, TypeScript code as well) out of your project's Prisma schema. You can watch this mechanism at play like this:

ls -l node_modules/.prisma/client/index.d.ts
rm node_modules/.prisma/client/index.d.ts
yarn codegen
ls -l node_modules/.prisma/client/index.d.ts

There is an equivalent yarn nexus:reflect command for Nexus-generated types under node_modules/@types/typegen-nexus*/index.d.ts. The workflow for the latter is quite a bit more involved (as it turns out, having to read the GraphQL schema out of TypeScript code causes a nice chicken-and-egg problem on types...); therefore, you might want to peruse the additional explanations available in the comments of ./nexus/schema.ts.

Cookbook

Logging SQL queries

DEBUG=prisma:query yarn start

Debugging the commands in the scripts section of package.json

The start and test scripts have explicit support for debuggability through the --inspect-brk flag:

yarn start --inspect-brk
yarn test --inspect-brk

Then, open Chrome and navigate to chrome://inspect.

As far as the other scripts (such as the yarn codegen steps) are concerned, the least intrusive way to pass --inspect-brk is through the NODE_OPTIONS environment variable — but be careful that you don't want to do that while using npx as that would cause a port conflict (whereby both npx itself, and then the actual debuggee you intended, would honor NODE_OPTIONS and try to bind() to the same local TCP port). You need to invoke the desired binary directly from the ./node_modules/.bin/ directory instead, e.g.

NODE_OPTIONS=--inspect-brk ./node_modules/.bin/prisma generate
NODE_OPTIONS=--inspect-brk ./node_modules/.bin/ts-node --transpile-only nexus/schema

Then, as previously, open chrome://inspect tab in Chrome.