Working with compound IDs and unique constraints

Composite IDs and compound unique constraints can be defined in your Prisma schema using the @@id and @@unique attributes.

:::warning

MongoDB does not support @@id

MongoDB does not support composite IDs, which means you cannot identify a model with a @@id attribute.

:::

A composite ID or compound unique constraint uses the combined values of two fields as a primary key or identifier in your database table. In the following example, the postId field and userId field are used as a composite ID for a Like table:

model User {
  id    Int    @id @default(autoincrement())
  name  String
  post  Post[]
  likes Like[]
}

model Post {
  id      Int    @id @default(autoincrement())
  content String
  User    User?  @relation(fields: [userId], references: [id])
  userId  Int?
  likes   Like[]
}

model Like {
  postId Int
  userId Int
  User   User @relation(fields: [userId], references: [id])
  Post   Post @relation(fields: [postId], references: [id])

  @@id([postId, userId]) // [!code highlight]
}

Querying for records from the Like table (e.g. using prisma.like.findMany()) would return objects that look as follows:

{
  "postId": 1,
  "userId": 1
}

Although there are only two fields in the response, those two fields make up a compound ID named postId_userId.

You can also create a named compound ID or compound unique constraint by using the @@id or @@unique attributes' name field. For example:

model Like {
  postId Int
  userId Int
  User   User @relation(fields: [userId], references: [id])
  Post   Post @relation(fields: [postId], references: [id])

  @@id(name: "likeId", [postId, userId]) // [!code highlight]
}

Where you can use compound IDs and unique constraints

Compound IDs and compound unique constraints can be used when working with unique data.

Below is a list of Prisma Client functions that accept a compound ID or compound unique constraint in the where filter of the query:

• findUnique()
• findUniqueOrThrow
• delete
• update
• upsert

A composite ID and a composite unique constraint is also usable when creating relational data with connect and connectOrCreate.

Filtering records by a compound ID or unique constraint

Although your query results will not display a compound ID or unique constraint as a field, you can use these compound values to filter your queries for unique records:

const like = await prisma.like.findUnique({
  where: {
    likeId: {
      userId: 1,
      postId: 1,
    },
  },
});

:::info

Note composite ID and compound unique constraint keys are only available as filter options for unique queries such as findUnique() and findUniqueOrThrow. See the section above for a list of places these fields may be used.

:::

Deleting records by a compound ID or unique constraint

A compound ID or compound unique constraint may be used in the where filter of a delete query:

const like = await prisma.like.delete({
  where: {
    likeId: {
      userId: 1,
      postId: 1,
    },
  },
});

Updating and upserting records by a compound ID or unique constraint

A compound ID or compound unique constraint may be used in the where filter of an update query:

const like = await prisma.like.update({
  where: {
    likeId: {
      userId: 1,
      postId: 1,
    },
  },
  data: {
    postId: 2,
  },
});

They may also be used in the where filter of an upsert query:

await prisma.like.upsert({
  where: {
    likeId: {
      userId: 1,
      postId: 1,
    },
  },
  update: {
    userId: 2,
  },
  create: {
    userId: 2,
    postId: 1,
  },
});

Filtering relation queries by a compound ID or unique constraint

Compound IDs and compound unique constraint can also be used in the connect and connectOrCreate keys used when connecting records to create a relationship.

For example, consider this query:

await prisma.user.create({
  data: {
    name: "Alice",
    likes: {
      connect: {
        likeId: {
          postId: 1,
          userId: 2,
        },
      },
    },
  },
});

The likeId compound ID is used as the identifier in the connect object that is used to locate the Like table's record that will be linked to the new user: "Alice".

Similarly, the likeId can be used in connectOrCreate's where filter to attempt to locate an existing record in the Like table:

await prisma.user.create({
  data: {
    name: "Alice",
    likes: {
      connectOrCreate: {
        create: {
          postId: 1,
        },
        where: {
          likeId: {
            postId: 1,
            userId: 1,
          },
        },
      },
    },
  },
});