Null and undefined

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
    },
  })
},

The effect of null and undefined on conditionals

There are some caveats to filtering with conditionals which might produce unexpected results. When filtering with conditionals you might expect one result but receive another given how Prisma treats nullable values.

The following table provides a high-level overview of how the different operators handle 0, 1 and n filters.

This example shows how an undefined parameter impacts the results returned by a query that uses the OR operator.

interface FormData {
  name: string;
  email?: string;
}

const formData: FormData = {
  name: 'Emelie'
}

const users = await prisma.user.findMany({
  where: {
    OR: [
      {
        email: {
          contains: formData.email
        }
      }
    ]
  }
})

// returns: []

The query receives filters from a formData object, which includes an optional email property. In this instance, the value of the email property is undefined. When this query is run no data is returned.

This is in contrast to the AND and NOT operators, which will both return all the users if you pass in an undefined value.

This is because passing an undefined value to an AND or NOT operator is the same as passing nothing at all, meaning the findMany query in the example will run without any filters and return all the users.

interface FormData {
  name: string;
  email?: string;
}

const formData: FormData = {
  name: 'Emelie'
}

const users = await prisma.user.findMany({
  where: {
    AND: [
      {
        email: {
          contains: formData.email
        }
      }
    ]
  }
})

// returns: { id: 1, email: 'ems@boop.com', name: 'Emelie' }

const users = await prisma.user.findMany({
  where: {
    NOT: [
      {
        email: {
          contains: formData.email
        }
      }
    ]
  }
})

// returns: { id: 1, email: 'ems@boop.com', name: 'Emelie' }