Differences in code between local project and Dockerized project break the app - node.js

Question

I'm trying to dockerize my current pet project in which I use a NodeJS (ExpressJS) as a backend, React as a frontend and PostgreSQL as a database. On both backend and frontend I use TypeScript instead of JavaScript. I'm also using a Prisma as ORM for my database. I decided to have a standard three container's architecture, one for backend, one for database and one for frontend app. My Dockerfile's are as follows:
Frontend's Dockerfile
FROM node:alpine
WORKDIR /usr/src/frontend
COPY package*.json ./
RUN npm install
COPY . .
EXPOSE 3000
CMD ["npm", "run", "start"]
Backend's Dockerfile
FROM node:lts
WORKDIR /usr/src/backend
COPY package*.json ./
RUN npm install
COPY . .
EXPOSE 8000
RUN npx prisma generate
CMD ["npm", "run", "dev"]
there's also a .dockerignore file in the backend folder:
node_modules/
and my docker-compose.yml looks like this:
version: '3.9'
services:
db:
image: 'postgres'
ports:
- '5432:5432'
environment:
POSTGRES_USER: 'postgres'
POSTGRES_PASSWORD: 'postgres'
POSTGRES_DB: 'hucuplant'
server:
build:
context: ./backend_express
ports:
- "8000:8000"
environment:
DATABASE_URL: 'postgresql://postgres:postgres#localhost:5432/hucuplant?schema=public'
client:
build:
context: ./frontend
ports:
- "3000:3000"
After doing a docker-compose up --build everything starts well but when I try to register a new user on my site then I get the following error:
Error:
hucuplant-server-1 | Invalid `prisma.user.findUnique()` invocation in
hucuplant-server-1 | /usr/src/backend/src/routes/Auth.ts:44:57
hucuplant-server-1 |
hucuplant-server-1 | 41 auth.post("/register", async (req: Request, res: Response) => {
hucuplant-server-1 | 42 const { email, username, password } = req.body;
hucuplant-server-1 | 43
hucuplant-server-1 | → 44 const usernameResult: User | null = await prisma.user.findUnique({
hucuplant-server-1 | where: {
hucuplant-server-1 | ? username?: String,
hucuplant-server-1 | ? id?: Int,
hucuplant-server-1 | ? email?: String
hucuplant-server-1 | }
hucuplant-server-1 | })
However, the existing code in my Auth.ts file on the line 44 looks like this:
auth.post("/register", async (req: Request, res: Response) => {
const { email, username, password } = req.body;
const usernameResult: User | null = await prisma.user.findUnique({
where: {
username: username,
},
});
When I run my project locally everything works just fine but when I try to run the containerized app then those things break and differ quite much. What is causing that? How do I fix that?