Datamigration without loss

[jkottapa]

Original schema

model Vendor {
  id        Int      @id @default(autoincrement())
  email     String   @unique
  imageUrl String?
  name      String?
  role      Role     @default(VENDOR)
  vendorStrings     VendorString[]
  createdAt DateTime @default(now())
  updatedAt DateTime @updatedAt
}

model VendorString {
  id         Int        @id @default(autoincrement())
  createdAt  DateTime   @default(now())
  updatedAt  DateTime   @updatedAt
  name      String  @unique
  vendor     Vendor      @relation(fields: [vendorId], references: [id])
  vendorId Int
}

enum Role {
  VENDOR
  ADMIN
}

I want to make the vendor attribute many-to-many relation instead of 1-many relation it is now.
Here is my new schema:

model Vendor {
  id        Int      @id @default(autoincrement())
  email     String   @unique
  imageUrl String?
  name      String?
  role      Role     @default(VENDOR)
  vendorStrings     VendorString[] @relation(references: [id])
  createdAt DateTime @default(now())
  updatedAt DateTime @updatedAt
}

model VendorString {
  id         Int        @id @default(autoincrement())
  createdAt  DateTime   @default(now())
  updatedAt  DateTime   @updatedAt
  name      String  @unique
  vendor     Vendor[]      @relation(references: [id])
}

enum Role {
  VENDOR
  ADMIN
}

How do I make it happen with prisma migrate without losing my existing relations already established?

[ryands17]

Hey @Jayanth1991
Currently prisma migrate doesn't support directly converting scalar fields to a list without data loss.
For that, you would have to run your migrations in the following manner.

• You would have to create a new array field first
• seed the converted data to the newly created field
• delete the non-required scalar field after all the data is seeded

This is currently the approach that you can follow to safely migrate from 1-n to m-n relations.

[ryanking1809]

I just came across this issue with migrating columns like name and transforming the data into firstName and lastName. Sounds like you already something in mind but would be amazing to be able to execute javascript functions between migration steps in the future!

Maybe something like this.

steps: [
   {
      "tag": "CreateField",
      "model": "User",
      "field": "firstName",
      "type": "String",
    },
    {
      "tag": "CreateField",
      "model": "User",
      "field": "lastName",
      "type": "String",
    },
    {
      "dataTransformer": splitUserNamesAndSave()
    },
    {
      "tag": "DeleteField",
      "model": "User",
      "field": "name",
    }
]