Prisma many-to-many relations: create and connect

user_188740 0
Viewed 23306

In my Prisma schema, I have a many-to-many relationship between posts and categories. I've added @map options to match the Postgres snake_case naming convention:

model Post {
  id         Int            @id @default(autoincrement())
  title      String
  body       String?
  categories PostCategory[]

  @@map("post")
}

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

  @@map("category")
}

model PostCategory {
  categoryId Int      @map("category_id")
  postId     Int      @map("post_id")
  category   Category @relation(fields: [categoryId], references: [id])
  post       Post     @relation(fields: [postId], references: [id])

  @@id([categoryId, postId])
  @@map("post_category")
}

I'm trying to create a post with multiple categories at the same time. If a category exists, I'd like to connect the category to the post. If the category doesn't exist, I'd like to create it. The creation part is working well, but the connection part is problematic:

  await prisma.post.create({
    data: {
      title: 'Hello',
      categories: {
        create: [{ category: { create: { name: 'News' } } }],
        connect: {
          categoryId_postId: { categoryId: 1, postId: ? }, // This doesn't work, even if I had the postId
        },
      },
    },
  });

How can I connect an existing category to a new post with the schema that I have?

prisma-graphql prisma2 prisma graphql typescript
5 Answers

What you need here is connectOrCreate.

So something like this should work:

      await prisma.post.create({
        data: {
          title: 'Hello',
          categories: {
            create: [
              {
                category: {
                  create: {
                    name: 'category-1',
                  },
                },
              },
              { category: { connect: { id: 10 } } },
            ],
          },
        },
      });

You can also read more about this in the docs here

user_88743510

This problem drove me up the wall so I'll contribute my solution here incase it helps someone else. First, read this: https://www.prisma.io/docs/concepts/components/prisma-schema/relations/many-to-many-relations

My schema is similar to the one in question, only difference is I have Files instead of Posts and Tags instead of Categories. To link the created file's tags to existing tags I used this:

  await Promise.all(DEFAULT_FILES[2].map(file => prisma.file.create({
    data: {
      ...file,
      user_id: userId,
      parent_id: homeFolder.id,
      tags: {
        create: file.tags?.map(name => ({
          tag: {
            connect: {
              id: tags.find(t => t.name === name)?.id
            }
          }
        }))
      },
    }
  })))
user_52532790 
await prisma.postCategory.create({
  data: {
    category: {
      connectOrCreate: {
        id: categoryId
      }
    },
    posts: {
      create: [
        {
          title: 'g3xxxxxxx',
          body: 'body g3xxxxx'
        }
      ],
    },
  },
})

You should connect to the existing record and then create the record that you want to be related with the first one.

https://www.prisma.io/docs/concepts/components/prisma-client/relation-queries (Connect an existing record)

user_178939050

Explicit many-to-many create/update existing tags read more here 

let args =[1,2,3,4]
tags: {
      create: args.tags?.map(tagId=>({
          tag:{
              connect:{
                  id:tagId
              }
          }
      }))
    },
 }

user_81862380

After hours of trying I finally came up with the following solution for my use case.

park[] <-> exercise[]

// create parks
await prisma.park.createMany({data: [...]})

// create and connect exercises
const exercises = [...];
await Promise.all([
  exercises.map(async (exercise) => {
    await prisma.exercise.create({
      data: <any>{
        ...exercise,
        parks: {
          connect: parks.map((park) => ({ id: park.id })),
        },
      },
    });
  }),
]);
user_128349720
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