How can I represent extra relation columns in a Prisma schema? - database

Question

I'm using Prisma 3.7.0 and Postgresql 13. I need to create a many-to-many relation between two models that has some additional data, but I don't know how to do this in a Prisma schema. The fields I want to add are not appropriately added to either table.
Here's some simplified (contrived) SQL to illustrate the goal:
It's pretty straight-forward in SQL, but I don't quite understand from the Prisma docs how to do it.
CREATE TABLE animal (
id SERIAL PRIMARY KEY,
name TEXT NOT NULL -- e.g. "tiger" or "armadillo"
)
CREATE TABLE animal_bodyparts (
animal INT,
bodypart INT,
-- I want to add these two fields to the relation.
count INT, -- How many of this bodypart the animal has
is_vital BOOLEAN, -- Does the creature die if this part is damaged?
PRIMARY KEY (animal, bodypart)
CONSTRAINT fk_animal FOREIGN KEY (animal) REFERENCES animal(id),
CONSTRAINT fk_bodypart FOREIGN KEY (bodypart) REFERENCES bodypart(id)
)
CREATE TABLE bodypart (
id SERIAL PRIMARY KEY,
name TEXT NOT NULL -- e.g. "head" or "leg"
)
And here's the best I could figure out with Prisma so far:
model Animal {
id Int #id #default(autoincrement)
name String // e.g. "tiger" or "armadillo"
parts BodyPart[]
}
model BodyPart {
id Int #id #default(autoincrement)
name String // e.g. "head" or "leg"
animals Animal[]
}
But where do I put the count and is_vital columns in the Prisma models? I see in a one-to-many relation there's some way to add some info through the #relation tag, but I don't think it addresses this need.

Answer 1

You can do it as follow:
datasource mysql {
provider = "mysql"
url = env("DATABASE_URL")
}
generator client {
provider = "prisma-client-js"
}
generator erd {
provider = "prisma-erd-generator"
output = "entity-relationship-diagram.svg"
}
model Animal {
id Int #id #default(autoincrement())
name String
animalAndBodyParts AnimalAndBodyParts[] #relation()
}
model AnimalAndBodyParts {
id Int #id #default(autoincrement())
count Int
isVital Boolean #map("is_vital")
animal Animal #relation(fields: [animalId], references: [id])
animalId Int
bodyPart BodyPart #relation(fields: [bodyPartId], references: [id])
bodyPartId Int
}
model BodyPart {
id Int #id #default(autoincrement())
name String
animalAndBodyParts AnimalAndBodyParts[] #relation()
}
It will generate a database as show the image:
You can save data in this way:
const { PrismaClient } = require('#prisma/client')
const prisma = new PrismaClient()
const saveData = async () => {
const animal = await prisma.animal.create({
data: {
name: 'Lion',
animalAndBodyParts: {
create: {
count: 2,
isVital: true,
bodyPart: {
create: {
name: 'Eye',
},
},
},
},
},
include: {
animalAndBodyParts: {
include: {
bodyPart: true,
},
},
},
})
console.log(JSON.stringify(animal, null, 2));
}
saveData()
And the data will look like in the image down below