Many-to-many relations

Relational databases ​

In relational databases, m-n-relations are typically modelled via relation tables . m-n-relations can be either explicit or implicit in the Prisma schema. We recommend using implicit m-n-relations if you do not need to store any additional meta-data in the relation table itself. You can always migrate to an explicit m-n-relation later if needed.

Explicit many-to-many relations ​

In an explicit m-n relation, the relation table is represented as a model in the Prisma schema and can be used in queries. Explicit m-n relations define three models:

The relation table CategoriesOnPosts connects related Post and Category records. In this example, the model representing the relation table also defines additional fields that describe the Post / Category relationship - who assigned the category ( assignedBy ), and when the category was assigned ( assignedAt ):

model Post {
  id         Int                 @id @default(autoincrement())
  title      String
  categories CategoriesOnPosts[]
}

model Category {
  id    Int                 @id




    
 @default(autoincrement())
  name  String
  posts CategoriesOnPosts[]
}

model CategoriesOnPosts {
  post       Post     @relation(fields: [postId], references: [id])
  postId     Int // relation scalar field (used in the `@relation` attribute above)
  category   Category @relation(fields: [categoryId], references: [id])
  categoryId Int // relation scalar field (used in the `@relation` attribute above)
  assignedAt DateTime @default(now())
  assignedBy String

  @@id([postId, categoryId])
}

The underlying SQL looks like this:

CREATE TABLE "Post" (
    "id" SERIAL NOT NULL,
    "title" TEXT NOT NULL,

    CONSTRAINT "Post_pkey" PRIMARY KEY ("id")
);

CREATE TABLE "Category" (
    "id" SERIAL NOT NULL,
    "name" TEXT NOT NULL,

    CONSTRAINT "Category_pkey" PRIMARY KEY ("id")
);


-- Relation table + indexes --

CREATE TABLE "CategoriesOnPosts" (
    "postId" INTEGER NOT NULL,
    "categoryId" INTEGER NOT NULL,
    "assignedAt" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
    "assignedBy" TEXT NOT NULL,

    CONSTRAINT "CategoriesOnPosts_pkey" PRIMARY KEY




    
 ("postId","categoryId")
);

ALTER TABLE "CategoriesOnPosts" ADD CONSTRAINT "CategoriesOnPosts_postId_fkey" FOREIGN KEY ("postId") REFERENCES "Post"("id") ON DELETE RESTRICT ON UPDATE CASCADE;
ALTER TABLE "CategoriesOnPosts" ADD CONSTRAINT "CategoriesOnPosts_categoryId_fkey" FOREIGN KEY ("categoryId") REFERENCES "Category"("id") ON DELETE RESTRICT ON UPDATE CASCADE;

Note that the same rules as for 1-n relations apply (because Post ↔ CategoriesOnPosts and Category ↔ CategoriesOnPosts are both in fact 1-n relations), which means one side of the relation needs to be annotated with the @relation attribute.

When you don't need to attach additional information to the relation, you can model m-n-relations as implicit m-n-relations . If you're not using Prisma Migrate but obtain your data model from introspection , you can still make use of implicit m-n-relations by following Prisma ORM's conventions for relation tables .

Querying an explicit many-to-many ​

The following section demonstrates how to query an explicit m-n-relation. You can query the relation model directly ( prisma.categoriesOnPosts(...) ), or use nested queries to go from Post -> CategoriesOnPosts -> Category or the other way.

The following query does three things:

const createCategory = await prisma.post.create({
  data: {
    title: 'How to be Bob',
    categories: {
      create: [
        {
          assignedBy: 'Bob',
          assignedAt: new Date(),
          category: {
            create: {
              name: 'New category',
            },
          },
        },
      ],
    },
  },
})

The following query:

const assignCategories = await prisma.




    
post.create({
  data: {
    title: 'How to be Bob',
    categories: {
      create: [
        {
          assignedBy: 'Bob',
          assignedAt: new Date(),
          category: {
            connect: {
              id: 9,
            },
          },
        },
        {
          assignedBy: 'Bob',
          assignedAt: new Date(),
          category: {
            connect: {
              id: 22,
            },
          },
        },
      ],
    },
  },
})

Sometimes you might not know if a Category record exists. If the Category record exists, you want to connect a new Post record to that category. If the Category record does not exist, you want to create the record first and then connect it to the new Post record. The following query:

const assignCategories = await prisma.post.create({
  data: {
    title: 'How to be Bob',
    categories: {
      create: [
        {
          assignedBy: 'Bob',
          assignedAt: new Date(),
          category: {
            connectOrCreate: {
              where: {
                id: 9,
              },
              create: {
                name: 'New Category',
                id: 9,
              },
            




    
},
          },
        },
      ],
    },
  },
})

The following query returns all Post records where at least one ( some ) category assignment ( categories ) refers to a category named "New category" :

const getPosts = await prisma.post.findMany({
  where: {
    categories: {
      some: {
        category: {
          name: 'New Category',
        },
      },
    },
  },
})

The following query returns all categories where at least one ( some ) related Post record titles contain the words "Cool stuff" and the category was assigned by Bob.

const getAssignments = await prisma.category.findMany({
  where: {
    posts: {
      some: {
        assignedBy: 'Bob',
        post: {
          title: {
            contains: 'Cool stuff',
          },
        },
      },
    },
  },
})

The following query gets all category assignments ( CategoriesOnPosts ) records that were assigned by "Bob" to one of 5 posts:

const getAssignments = await prisma.categoriesOnPosts.findMany({
  where: {
    assignedBy: 'Bob',
    post: {
      id: {
        




    
in: [9, 4, 10, 12, 22],
      },
    },
  },
})

Implicit many-to-many relations ​

Implicit m-n relations define relation fields as lists on both sides of the relation. Although the relation table exists in the underlying database, it is managed by Prisma ORM and does not manifest in the Prisma schema . Implicit relation tables follow a specific convention .

Implicit m-n-relations makes the Prisma Client API for m-n-relations a bit simpler (since you have one fewer level of nesting inside of nested writes ).

In the example below, there's one implicit m-n-relation between Post and Category :

model Post {
  id         Int        @id @default(autoincrement())
  title      String
  categories Category[]
}

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

model Post {
  id          String     @id @default(auto()) @map("_id") @db.ObjectId
  categoryIDs String[]   @db.ObjectId
  categories  Category[] @relation(fields: [categoryIDs], references: [id])
}

model Category {
  id      String   @id @default(auto()) @map("_id") @db.ObjectId
  name    String
  postIDs String[] @db.ObjectId
  posts   Post[]   @relation(fields: [postIDs], references: [id])
}




    

Querying an implicit many-to-many ​

The following section demonstrates how to query an implicit m-n relation. The queries require less nesting than explicit m-n queries .

The following query creates a single Post and multiple Category records:

const createPostAndCategory = await prisma.post.create({
  data: {
    title: 'How to become a butterfly',
    categories: {
      create: [{ name: 'Magic' }, { name: 'Butterflies' }],
    },
  },
})

The following query creates a single Category and multiple Post records:

const createCategoryAndPosts = await prisma.category.create({
  data: {
    name: 'Stories',
    posts: {
      create: [
        { title: 'That one time with the stuff' },
        { title: 'The story of planet Earth' },
      ],
    },
  },
})

The following query returns all Post records with a list of that post's assigned categories:

const getPostsAndCategories = await prisma.post.findMany({
  include: {
    categories: true,
  },
})

Rules for defining an implicit m-n relation ​

Implicit m-n relations:

Use a specific convention for relation tables

Do not require the @relation attribute unless you need to disambiguate relations with a name, e.g. @relation("MyRelation") or @relation(name: "MyRelation") .

If you do use the @relation attribute, you cannot use the references , fields , onUpdate or onDelete arguments. This is because these take a fixed value for implicit m-n-relations and cannot be changed.

Require both models to have a single @id . Be aware that:

Conventions for relation tables in implicit m-n relations ​

If you obtain your data model from introspection , you can still use implicit m-n-relations by following Prisma ORM's conventions for relation tables . The following example assumes you want to create a relation table to get an implicit m-n-relation for two models called Post and Category .

Relation table ​

If you want a relation table to be picked up by introspection as an implicit m-n-relation, the name must follow this exact structure:

In the example, the correct table name is _CategoryToPost .

When creating an implicit m-n-relation yourself in the Prisma schema file, you can configure the relation to have a different name. This will change the name given to the relation table in the database. For example, for a relation named "MyRelation" the corresponding table will be called _MyRelation .

Multi-schema ​

If your implicit many-to-many relationship spans multiple database schemas (using the multiSchema preview feature ), the relation table (with the name defined directly above, in the example _CategoryToPost ) must be present in the same database schema as the first model in alphabetical order (in this case Category ).

Columns ​

A relation table for an implicit m-n-relation must have exactly two columns:

The columns must be called A and B where A points to the model that comes first in the alphabet and B points to the model which comes last in the alphabet.

Indexes ​

There further must be:

A unique index defined on both foreign key columns:

CREATE UNIQUE INDEX "_CategoryToPost_AB_unique" ON "_CategoryToPost"("A" int4_ops,"B" int4_ops);

A non-unique index defined on B:

CREATE INDEX "_CategoryToPost_B_index" ON "_CategoryToPost"("B" int4_ops);

Example ​

This is a sample SQL statement that would create the three tables including indexes (in PostgreSQL dialect) that are picked up as a implicit m-n-relation by Prisma Introspection:

CREATE TABLE "_CategoryToPost" (
    "A" integer NOT NULL REFERENCES "Category"(id) ,
    "B" integer NOT NULL REFERENCES "Post"(id)
);
CREATE UNIQUE INDEX "_CategoryToPost_AB_unique" ON "_CategoryToPost"("A" int4_ops,"B" int4_ops);
CREATE INDEX "_CategoryToPost_B_index" ON "_CategoryToPost"("B" int4_ops);

CREATE TABLE "Category" (
    id 




    
integer SERIAL PRIMARY KEY
);

CREATE TABLE "Post" (
    id integer SERIAL PRIMARY KEY
);

And you can define multiple many-to-many relations between two tables by using the different relationship name. This example shows how the Prisma introspection works under such case:

CREATE TABLE IF NOT EXISTS "User" (
    "id" SERIAL PRIMARY KEY
);
CREATE TABLE IF NOT EXISTS "Video" (
    "id" SERIAL PRIMARY KEY
);
CREATE TABLE IF NOT EXISTS "_UserLikedVideos" (
    "A" SERIAL NOT NULL,
    "B" SERIAL NOT NULL,
    CONSTRAINT "_UserLikedVideos_A_fkey" FOREIGN KEY ("A") REFERENCES "User" ("id") ON DELETE CASCADE ON UPDATE CASCADE,
    CONSTRAINT "_UserLikedVideos_B_fkey" FOREIGN KEY ("B") REFERENCES "Video" ("id") ON DELETE CASCADE ON UPDATE CASCADE
);
CREATE TABLE IF NOT EXISTS "_UserDislikedVideos" (
    "A" SERIAL NOT NULL,
    "B" SERIAL NOT NULL,
    CONSTRAINT "_UserDislikedVideos_A_fkey" FOREIGN KEY ("A") REFERENCES "User" ("id") ON DELETE CASCADE ON UPDATE CASCADE,
    CONSTRAINT "_UserDislikedVideos_B_fkey" FOREIGN KEY ("B") REFERENCES "Video" ("id") ON DELETE CASCADE ON UPDATE CASCADE
);
CREATE




    
 UNIQUE INDEX "_UserLikedVideos_AB_unique" ON "_UserLikedVideos"("A", "B");
CREATE INDEX "_UserLikedVideos_B_index" ON "_UserLikedVideos"("B");
CREATE UNIQUE INDEX "_UserDislikedVideos_AB_unique" ON "_UserDislikedVideos"("A", "B");
CREATE INDEX "_UserDislikedVideos_B_index" ON "_UserDislikedVideos"("B");

If you run prisma db pull on this database, the Prisma CLI will generate the following schema through introspection:

model User {
  id                       Int     @id @default(autoincrement())
  Video_UserDislikedVideos Video[] @relation("UserDislikedVideos")
  Video_UserLikedVideos    Video[] @relation("UserLikedVideos")
}

model Video {
  id                      Int    @id @default(autoincrement())
  User_UserDislikedVideos User[] @relation("UserDislikedVideos")
  User_UserLikedVideos    User[] @relation("UserLikedVideos")
}

Configuring the name of the relation table in implicit many-to-many relations ​

When using Prisma Migrate, you can configure the name of the relation table that's managed by Prisma ORM using the @relation attribute. For example, if you want the relation table to be called _MyRelationTable instead of the default name _CategoryToPost , you can specify it as follows:

model Post {
  id         Int        @id @default(autoincrement())
  categories Category[] @relation("MyRelationTable")
}

model Category {
  id    Int    @id @default(autoincrement())
  posts Post[] @relation("MyRelationTable")
}

Relation tables ​

A relation table (also sometimes called a JOIN , link or pivot table) connects two or more other tables and therefore creates a relation between them. Creating relation tables is a common data modelling practice in SQL to represent relationships between different entities. In essence it means that "one m-n relation is modeled as two 1-n relations in the database".

We recommend using implicit m-n-relations, where Prisma ORM automatically generates the relation table in the underlying database. Explicit m-n-relations should be used when you need to store additional data in the relations, such as the date the relation was created.

MongoDB ​

In MongoDB, m-n-relations are represented by:

The following example demonstrates a m-n-relation between posts and categories:

model Post {
  id          String     @id @default(auto()) @map("_id") @db.ObjectId
  categoryIDs String[]   @db.ObjectId
  categories  Category[] @relation(fields: [categoryIDs], references: [id])
}

model Category {
  id      String   @id @default(auto()) @map("_id") @db.ObjectId
  name    String
  postIDs String[] @db.ObjectId
  posts   Post[]   @relation(fields: [postIDs], references: [id])
}

Prisma ORM validates m-n-relations in MongoDB with the following rules:

The implicit m-n-relations used in relational databases are not supported on MongoDB.

Querying MongoDB many-to-many relations ​

This section demonstrates how to query m-n-relations in MongoDB, using the example schema above.