I am using Meteor 1.8 and the error above is coming because I am using persistent-minimongo.
My use case for persistent minimongo is to use it not only for offline support but to also use it as cache for slow networks. Now the problem happens when user is online and loads the page, persistent-minimongo starts writing data from indexed-db(or similar browser storage) to minimongo while subscriptions too start writing to minimongo, in which case there is a conflict if persitent-minimono wrote any document first in minimongo and we receive the above error.
To fix this I have cloned mongo inside packages folder of my project and made changes to collection.js. Below is the part of the code which was throwing the above error.
Object.assign(Mongo.Collection.prototype, {
_maybeSetUpReplication(name, {
_suppressSameNameError = false
}) {
....
....
update(msg) {
....
....
} else if (msg.msg === 'added') {
if (doc) {
throw new Error("Expected not to find a document already present for an add");
}
self._collection.insert({ _id: mongoId, ...msg.fields });*
}
...
...
I changed the above part of the code to not thorw an error as shown below.
else if (msg.msg === 'added') {
if (doc) {
self._collection.remove(mongoId)
}
self._collection.insert({ _id: mongoId, ...msg.fields });
Note: I do not want to make change to meteor core packages but I could not find any better solution.
The above change fixed my issue but I am a little worried about the repercussion of the above change. Want to understand as to why an error is thrown rather than replacing the document.
Any help would be appreciated. Thanks in advance!!