PrismaP
Prisma•2y ago•
2 replies
tort6334

Solve optimistic concurrency issue without adding a `version` field

Question


In the following page there is a suggestion how to solve concurrency issue by adding a version field and ask about it in the 
where
 clause when updating a model: 

const userEmail = 'alice@prisma.io'
const movieName = 'Hidden Figures'

// Find the first available seat
// availableSeat.version might be 0
const availableSeat = await client.seat.findFirst({
  where: {
    Movie: {
      name: movieName,
    },
    claimedBy: null,
  },
})

if (!availableSeat) {
  throw new Error(`Oh no! ${movieName} is all booked.`)
}

// Only mark the seat as claimed if the availableSeat.version
// matches the version we're updating. Additionally, increment the
// version when we perform this update so all other clients trying
// to book this same seat will have an outdated version.
const seats = await client.seat.updateMany({
  data: {
    claimedBy: userEmail,
    version: {
      increment: 1,
    },
  },
  where: {
    id: availableSeat.id,
    version: availableSeat.version, // This version field is the key; only claim seat if in-memory version matches database version, indicating that the field has not been updated
  },
})

if (seats.count === 0) {
  throw new Error(`That seat is already booked! Please try again.`)
}

Reference: https://www.prisma.io/docs/orm/prisma-client/queries/transactions#optimistic-concurrency-control

what I want to ask, is if instead of doing:
  where: {
    id: availableSeat.id,
    version: availableSeat.version, // This version field is the key; only claim seat if in-memory version matches database version, indicating that the field has not been updated
  },


I could have asked if claimedBy is still null, will it do the same trick?
so the solution would be like so:
  where: {
    id: availableSeat.id,
    claimedBy: null
  },


The only disadvantage compared to version is that if there were many swaps between claimedby and null, i would have not known about it, but that's fine by me I guess?
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