How to make a rethinkdb atomic update if document exists, insert otherwise? - rethinkdb

Question

How to make a rethinkdb atomic update if document exists, insert otherwise?
I want to do something like:
var tab = r.db('agflow').table('test');
r.expr([{id: 1, n: 0, x: 11}, {id: 2, n: 0, x: 12}]).forEach(function(row){
var _id = row('id');
return r.branch(
tab.get(_id).eq(null), // 1
tab.insert(row), // 2
tab.get(_id).update(function(row2){return {n: row2('n').add(row('n'))}}) // 3
)})
However this is not fully atomic, because between the time when we check if document exists (1) and inserting it (2) some other thread may insert it.
How to make this query atomic?

Answer 1

I think the solution is passing
conflict="update"
to the insert method.
Als see RethinkDB documentation on insert

Answer 2

To make the inner part atomic, you can use replace:
tab.get(_id).replace(function(row2){
return r.expr({id: _id, n: row2('n').add(row('n'))})
.default(row)
})
Using replace is the only way at the moment to perform fully atomic upserts with non-trivial update operations.

Answer 3

This is a standard database operation called an "upsert".
Does RethinkDB support upserts?
Another question from Sergio
Tulentsev. The first public release didn't include support for
upserts, but now it can be done by passing an extra flag to insert:
r.table('marvel').insert({
superhero: 'Iron Man',
superpower: 'Arc Reactor'
}, {upsert: true}).run()
When set to true, the new document
from insert will overwrite the existing one.
cite: Answers to common questions about RethinkDB

Answer 4

OK, I figured out how to do it.
The solution is to firstly try insert, and if it fail we make update:
var tab = r.db('agflow').table('test');
tab.delete();
r.expr([{id: 1, n: 0, x: 11}, {id: 2, n: 0, x: 12}]).forEach(function(row){
var _id = row('id');
var res = tab.insert(row);
return r.branch(
res('inserted').eq(1),
res,
tab.get(_id).update(function(row2){return {n: row2('n').add(1)}})
)})