CODEWITHSUNDEEP
rethinkdb
Aler
Aler

Reputation: 15547

Document concurrent update

I have a document like:

{
  owner: 'alex',
  live:  'some guid'
}

Two or more users can update live field simultaneously.

How can I make sure that only the first user wins and others updates fails?

Upvotes: 0

Views: 131

Answers (1)

deontologician
deontologician

Reputation: 2814

You can get the semantics you want if you store some variable like "times_updated" in the document. Operations on a single document are atomic, so you can check that the field is the value you expect, and then throw an error if it isn't.

It might look something like:

var timesUpdated = 3

r.table('foo').get(rowId).update(function(row) {
     return r.branch(row('timesUpdated').eq(timesUpdated),
          {
              timesUpdated: row('timesUpdated').add(1),
              live: 'some special value'
          },
          r.error('Someone else updated the live field!')
     );
}, {returnChanges: true})

So if another query comes in before you for timesUpdated = 3, your query will blow up. When do you get timesUpdated? That depends on how your app is designed, and what you're trying to do.

Another thing to note is that adding {returnChanges: true} is really useful because it allows you to get the new value of timesUpdated atomically. You can also see what exactly changed in the updated document.

Upvotes: 1

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