Solve Prisma “ERROR: column “x” of relation “y” contains null values”

Have you faced such an error while applying migrations to the production database?

Database error:
ERROR: column "x" of relation "y" contains null values

or this warning message in the migration SQL file?

Added the required column x to the y table without a default value. This is not possible if the table is not empty.

Let’s dive into the situation and problem.

To start with I am going to reproduce this error. Initial source code.

1. I have 2 models:

generator client {
  provider = "prisma-client-js"
}

datasource db {
  provider = "postgresql"
  url      = env("DATABASE_URL")
}

model User {
  id        Int      @id @default(autoincrement())
  email     String   @unique
  name      String
  createdAt DateTime @default(now()) @map(name: "created_at")

  @@map(name: "users")
}

model Task {
  id          Int      @id @default(autoincrement())
  title       String
  description String
  createdAt   DateTime @default(now()) @map(name: "created_at")

  @@map(name: "tasks")
}

2. Generate initial migration

npx prisma migrate dev --name init

3. Apply migration in the production database (change production database URL in .env file)

npx prisma migrate deploy

4. Add data in production users and tasks table from API endpoint. I used Postman tool.

5. Our application business logic is changed, and I want to make changes in Prisma file. Added Tasks reference in User model and required user reference in Task model.

generator client {
  provider = "prisma-client-js"
}

datasource db {
  provider = "postgresql"
  url      = env("DATABASE_URL")
}

model User {
  id        Int      @id @default(autoincrement())
  email     String   @unique
  name      String
  createdAt DateTime @default(now()) @map(name: "created_at")

  Tasks Task[]

  @@map(name: "users")
}

model Task {
  id          Int      @id @default(autoincrement())
  title       String
  description String
  createdAt   DateTime @default(now()) @map(name: "created_at")

  userId Int  @map("user_id")
  User   User @relation(fields: [userId], references: [id], onDelete: Cascade)

  @@map(name: "tasks")
}

6. Let’s create a migration for this change:

npx prisma migrate dev --name task

It ran successfully. Because there is no data in my local database.

Let’s look at the migration file:

/*
  Warnings:

  - Added the required column `user_id` to the `tasks` table without a default value. This is not possible if the table is not empty.

*/
-- AlterTable
ALTER TABLE "tasks" ADD COLUMN     "user_id" INTEGER NOT NULL;

-- AddForeignKey
ALTER TABLE "tasks" ADD CONSTRAINT "tasks_user_id_fkey" FOREIGN KEY ("user_id") REFERENCES "users"("id") ON DELETE CASCADE ON UPDATE CASCADE;

It includes a warning message.

7. Let’s try to apply this migration to the production database with data (tasks table).

Oh noooooo. We have a huge problem.

The problem is we want to add the required ‘user_id’ in tasks table. That’s why Prisma migration stopped.

Solution steps (Reference)

1. Create the fields first as optional and then run migrate
2. Fill the fields first with the required data.
3. Remove the optional (?) from the field.

—

1. Let’s go back 5-step, and make the correct migration change for the initial step.

generator client {
  provider = "prisma-client-js"
}

datasource db {
  provider = "postgresql"
  url      = env("DATABASE_URL")
}

model User {
  id        Int      @id @default(autoincrement())
  email     String   @unique
  name      String
  createdAt DateTime @default(now()) @map(name: "created_at")

  Tasks Task[]

  @@map(name: "users")
}

model Task {
  id          Int      @id @default(autoincrement())
  title       String
  description String
  createdAt   DateTime @default(now()) @map(name: "created_at")

  userId Int?  @map("user_id")
  User   User? @relation(fields: [userId], references: [id], onDelete: Cascade)

  @@map(name: "tasks")
}

2. Create migration

npx prisma migrate dev --name optional-user

3. Apply latest migration to production database

npx prisma migrate deploy

Now, it user_id column is added

4. Fill rows with some default value. You can write script to fill the values.

5. Let’s remove the optional field in Prisma

generator client {
  provider = "prisma-client-js"
}

datasource db {
  provider = "postgresql"
  url      = env("DATABASE_URL")
}

model User {
  id        Int      @id @default(autoincrement())
  email     String   @unique
  name      String
  createdAt DateTime @default(now()) @map(name: "created_at")

  Tasks Task[]

  @@map(name: "users")
}

model Task {
  id          Int      @id @default(autoincrement())
  title       String
  description String
  createdAt   DateTime @default(now()) @map(name: "created_at")

  userId Int  @map("user_id")
  User   User @relation(fields: [userId], references: [id], onDelete: Cascade)

  @@map(name: "tasks")
}

6. Create migration

npx prisma migrate dev --name remove-optional-user

7. Apply latest migration to production database

npx prisma migrate deploy

Finally, we solved the error.