Reputation: 3923
I am trying to write the results of a MongoDB query to a file using the native Node.js driver. My code is the following (based on this post: Writing files in Node.js):
var query = require('./queries.js');
var fs = require('fs');
var MongoClient = require('mongodb').MongoClient;
MongoClient.connect("mongodb://localhost:27017/test", function(err, db) {
if(err) { return console.dir(err); }
var buildsColl = db.collection('blah');
collection.aggregate(query.test, function(err, result) {
var JSONResult = JSON.stringify(result);
//console.log(JSONResult);
fs.writeFile("test.json", JSONResult, function(err) {
if(err) {
console.log(err);
} else {
console.log("The file was saved!");
}
});
});
collection.aggregate(query.next, function(err, result) {
var JSONResult = JSON.stringify(result);
//console.log(JSONResult);
db.close();
});
});
The file is written, but the contents are 'undefined.' Printing the result to the console works though.
Upvotes: 4
Views: 2526
Reputation: 3923
For anyone stumbling across this the solution on where to put the db.close() is below:
collection.aggregate(query.test, function(err, result) {
var JSONResult = JSON.stringify(result);
//console.log(JSONResult);
fs.writeFile("test.json", JSONResult, function(err) {
if(err) {
console.log(err);
} else {
console.log("The file was saved!");
}
});
collection.aggregate(query.next, function(err, result) {
var JSONResult = JSON.stringify(result);
//console.log(JSONResult);
db.close();
});
});
Upvotes: 2
Reputation: 14718
Your code is not checking the err
on the aggregate callback.
You are likely getting an Mongo error and the result is undefined
in that case...
Other thing I could suspect is that you are getting multiple callbacks -- each one of them creates a new files, erasing the content.
Try using fs.appendFile
instead of fs.writeFile
and see if you are getting the expected data (plus the unwanted undefined
)
Upvotes: 2