Evolve your schema for a SQL Server database in a Typescript project

Add a `Tag` model to your schema

In this section, you will evolve your Prisma schema and then generate and apply the migration to your database with prisma migrate dev.

For the purpose of this guide, we'll make the following changes to the Prisma schema:

Create a new model called Tag with the following fields:
- id: an auto-incrementing integer that will be the primary key for the model
- name: a non-null String
- posts: an implicit many-to-many relation field that links to the Post model
Update the Post model with a tags field with an implicit many-to-many relation field that links to the Tag model

Once you've made the changes to your schema, your schema should resemble the one below:

prisma/schema.prisma

model Post {
  id        Int      @id @default(autoincrement())
  title     String   @db.VarChar(255)
  createdAt DateTime @default(now()) @db.Timestamp(6)
  content   String?
  published Boolean  @default(false)
  authorId  Int
  user      User     @relation(fields: [authorId], references: [id])
  tags      Tag[]
}

model Profile {
  id     Int     @id @default(autoincrement())
  bio    String?
  userId Int     @unique
  user   User    @relation(fields: [userId], references: [id])
}

model User {
  id      Int      @id @default(autoincrement())
  name    String?  @db.VarChar(255)
  email   String   @unique @db.VarChar(255)
  post    Post[]
  profile Profile?
}

model Tag {
  id    Int    @id @default(autoincrement())
  name  String
  posts Post[]
}

To apply your Prisma schema changes to your database, use the prisma migrate dev CLI command:

npx prisma migrate dev --name tags-model

This command will:

Create a new SQL migration file for the migration
Apply the generated SQL migration to the database
Regenerate Prisma Client

The following migration will be generated and saved in your prisma/migrations folder:

prisma/migrations/TIMESTAMP_tags_model.sql

 -- CreateTable
CREATE TABLE [dbo].[Tag] (
    [id] SERIAL NOT NULL,
    [name] VARCHAR(255) NOT NULL,

    CONSTRAINT [Tag_pkey] PRIMARY KEY ([id])
);

-- CreateTable
CREATE TABLE [dbo].[_PostToTag] (
    [A] INTEGER NOT NULL,
    [B] INTEGER NOT NULL
);

-- CreateIndex
CREATE UNIQUE INDEX [_PostToTag_AB_unique] ON _PostToTag([A], [B]);

-- CreateIndex
CREATE INDEX [_PostToTag_B_index] ON [_PostToTag]([B]);

-- AddForeignKey
ALTER TABLE [dbo].[_PostToTag] ADD CONSTRAINT [_PostToTag_A_fkey] FOREIGN KEY ([A]) REFERENCES [dbo].[Post]([id]) ON DELETE CASCADE ON UPDATE CASCADE;

-- AddForeignKey
ALTER TABLE [dbo].[_PostToTag] ADD CONSTRAINT [_PostToTag_B_fkey] FOREIGN KEY ([B]) REFERENCES [dbo].[Tag]([id]) ON DELETE CASCADE ON UPDATE CASCADE;

Congratulations, you just evolved your database with Prisma Migrate 🚀

Add a Tag model to your schema​

Add a `Tag` model to your schema