CODEWITHSUNDEEP
javascriptpouchdb
CristosLC
CristosLC

Reputation: 422

PouchDB gives 409 "Document update conflict" error with .put(), even with correct ._rev

I have a function that may either create or update documents in PouchDB, as follows. The function works perfectly when run the first time. However, every subsequent run yields a 409 error, even though the ._rev property appears to be correct. 

function saveEventMatchesToDatabase(event, db) {
    /* event: An event object from The Blue Alliance API. */
    /* db: a reference ot the PouchDB database. */

    /* Purpose: Given an event, extract the list of matches and teams, and save them to the database. */
    TBA.event.matches(event.key, function(matches_list) {
        var i = 0;
        for (i = 0; i < matches_list.length; i++) {
            var match = new Object();
            var docrec = new Object();

            match._id = 'matches/' + matches_list[i].key;
            match.redTeam = matches_list[i].alliances.red.teams;
            match.blueTeam = matches_list[i].alliances.blue.teams;

            /* If the doc already exists, we need to add the _rev to update the existing doc. */
            db.get(match._id).then(function(doc) {
                match._rev = doc._rev;
                docrec = doc;
            }).catch(function(err) {
                if ( err.status != 404 ) {
                    /* Ignore 404 errors: we expect them, if the doc is new. */
                    console.log(err);
                }
            });

            db.put(match).then(function() {
                // Success!
            }).catch(function(err) {
                console.log('\ndoc._rev: ' + docrec._rev);
                console.log('match._rev: ' + match._rev);
                console.log(err);
            });
        }
    });
}

Sample console output from running this function the second time is below. The same error occurs for EVERY item in match_list, not just intermittently.

doc._rev: 1-7cfa2c6245dd939d8489159d8ca674d9
match._rev: 1-7cfa2c6245dd939d8489159d8ca674d9
r {status: 409, name: "conflict", message: "Document update conflict", error: true}

I'm not sure what I'm missing, that's causing this problem. Any suggestions for where to look next would be greatly appreciated.

Upvotes: 6

Views: 9932

Answers (1)

nlawson
nlawson

Reputation: 11620

The first problem seems to be that you're using a function within a loop, meaning that any variables used inside of the inner functions are randomly changing under your feet depending on when the function gets invoked. Instead of a for loop, you can use forEach().

However, the second problems is that you are not using promises correctly; you need to wait for the result of get() before you do your put(). So probably forEach() is not even what you want in the first place; you probably want to use Promise.all() and then compose your promises.

I wrote a piece on this awhile back; many people have told me that it's worth reading even though it's long: "We have a problem with promises." Read that, and you should hopefully understand promises by the end of it. :)

Upvotes: 13

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