Middleware

Examples

Reference

params accepts the following type:

export type MiddlewareParams = {
  model?: ModelName
  action: PrismaAction
  args: any
  dataPath: string[]
  runInTransaction: boolean
}
export declare const ModelName: {
  User: 'User',
  Post: 'Post'
}
export declare type ModelName = (typeof ModelName)[keyof typeof ModelName]

Example:

{
  args: { where: { id: 15 } },
  dataPath: [ 'select', 'author', 'select', 'posts' ],
  runInTransaction: false,
  action: 'findMany',
  model: 'Post'
}

Parameter descriptions:

Tip: If you need the model property as a string, use: String(params.model)

Running order

If you have multiple middlewares, the running order for each separate query is:

1. All logic before await next(params)
2. All logic after await next(params)

const prisma = new PrismaClient()
prisma.$use(async (params, next) => {
  console.log(params.args.data.title)
  console.log('1')
  const result = await next(params)
  console.log('4')
  return result
})
prisma.$use(async (params, next) => {
  console.log('2')
  const result = await next(params)
  console.log('3')
  return result
})
const create = await prisma.post.create({
  data: {
    title: 'Welcome to Prisma Day 2020',
  },
})
const create2 = await prisma.post.create({
  data: {
    title: 'How to Prisma!',
  },
})

Output:

Welcome to Prisma Day 2020
1
2
3
4
How to Prisma!
1
2
3
4

Performance and appropriate use cases

Middleware executes for every query, which means that overuse has the potential to negatively impact performance. To avoid adding performance overheads:

• Check the params.model and params.action properties early in your middleware to avoid running logic unnecessarily:

  prisma.$use(async (params, next) => {
    if (params.model == 'Post' && params.action == 'delete') {
      // Logic only runs for delete action and Post model
    }
    return next(params)
  })

• Consider whether middleware is the appropriate solution for your scenario. For example:

  • If you need to populate a field, can you use the @default attribute?
  • If you need to set the value of a DateTime field, can you use the now() function or the @updatedAt attribute?
  • If you need to perform more complex validation, can you use a CHECK constraint in the database itself?