Working with One-to-Many Relations
1. Defining One-to-Many Relation
model User { id Int @id @default(autoincrement()) posts Post[] } model Post { id Int @id @default(autoincrement()) authorId Int author User @relation(fields: [authorId], references: [id], onDelete: Cascade) }
Side Marker Parent (one) List field Post[] Child (many) FK + @relation
2. Setting Foreign Key Field
Tip Detail Index FK columns auto-indexed for joins Composite FK Use array in fields/references
3. Configuring Back Reference
Side Field User.posts Virtual relation, no DB column Post.author Virtual; FK is authorId
4. Using Optional Foreign Keys
authorId Int? author User? @relation(fields: [authorId], references: [id], onDelete: SetNull)
Effect Detail Detached posts Posts can exist without an author Cascade choice Pair optional FK with SetNull
5. Setting Relation Name
Use Case Example Author + reviewer Two User relations on Post need names Syntax @relation("AuthoredPosts", fields:[authorId], references:[id])
6. Configuring Referential Actions
Scenario Recommendation User deleted → posts Cascade (remove posts) Author optional SetNull Audit log Restrict (preserve history)
const user = await prisma.user. findUnique ({ where: { id: 1 }, include: { posts: { where: { published: true }, take: 10 , orderBy: { createdAt: "desc" } } } });
Option Detail whereFilter included rows take/skipLimit/offset included rows orderBySort included rows
Operator Meaning someAt least one related row matches everyAll related rows match noneZero related rows match is/isNotFor to-one relations
await prisma.user. findMany ({ where: { posts: { some: { published: true } } } });
const users = await prisma.user. findMany ({ include: { _count: { select: { posts: true } } } });
Pattern Detail _countUse inside include or select Filtered count Pass where: { posts: { where: { published: true } } }
await prisma.user. findMany ({ orderBy: { posts: { _count: "desc" } } });
Pattern Use _countSort by number of related rows Related field orderBy: { author: { name: "asc" } }