Null and undefined (Reference)

Prisma Client differentiates between null and undefined:

null is a value
undefined means do nothing

Note: This is particularly important to account for in a Prisma with GraphQL context, where null and undefined are interchangeable.

In the following example, if emailInput is null, the query sets email (a mandatory field) to undefined - which means ✔ do not include this in the update:

const update = await prisma.user.update({
  where: {
    id: 1,
  },
  data: {
    name: "Petunia",
   email: emailInput != null ? emailInput : undefined, // If null, don't include in update!
  },
});
function getEmail() {
  const random = Math.floor(Math.random() * 10);
  if (random > 5) {
    return "ariadne@prisma.io"; // Could be null!
  }
  return null;
}

Setting a field value to undefined is the same as not including the email property in the update query at all:

const update = await prisma.user.update({
  where: {
    id: 1,
  },
  data: {
    name: "Petunia",
 // No email update here...
  },
});
function getEmail() {
  const random = Math.floor(Math.random() * 10);
  if (random > 5) {
    return "ariadne@prisma.io"; // Could be null!
  }
  return null;
}

By contrast, the following would ✘ not work as the mandatory email field cannot be null:

email: isValid(emailInput) ? emailInput : null, // email is a mandatory field!

Note: TypeScript will give you an error in this scenario: Type 'null' is not assignable to type 'string'. ts(2322)

Expand for sample schema

model User {
  email String  @unique
  id    Int     @default(autoincrement()) @id
  name  String?
  posts Post[]
}
model Post {
  id       String @default(cuid()) @id
  title    String
  authorId Int?
  views    Int?
  author   User?  @relation(fields: [authorId], references: [id])
}

Use case: null and undefined in a GraphQL resolver

In the following example mutation that updates a user, both authorEmail and name accept null - from a GraphQL perspective, this means that fields are optional:

type Mutation {
  // Update author's email or name, or both - or neither!
  updateUser(id: Int!, authorEmail: String, authorName: String): User!
}

However, if you pass null values for authorEmail or authorName on to Prisma, the following will happen:

If args.authorEmail is null, the query will fail - email does not accept null ✘
If args.authorName is null, Prisma changes the value of name to null - this is probably not how you want an update to work ✘

updateUser: (parent, args, ctx: Context) => {
  return ctx.prisma.user.update({
    where: { id: Number(args.id) },
    data: { 
     email: args.authorEmail, // email cannot be null
     name: args.authorName // name set to null - potentially unwanted behavior
     },
  })
},

Instead, set the value of email and name to undefined if the input value is null. Doing this is the same as not updating the field at all:

updateUser: (parent, args, ctx: Context) => {
  return ctx.prisma.user.update({
    where: { id: Number(args.id) },
    data: { 
     email: args.authorEmail != null ? args.authorEmail : undefined, // If null, do nothing
     name: args.authorName != null ? args.authorName : undefined // If null, do nothing
     },
  })
},

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Null and undefined

Use case: null and undefined in a GraphQL resolver

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