I used following method to create a node in Neo4j using nodejs. I want to create a node with its label as well as some property.
var query = [
"CREATE (n:TYPE {props})",
"RETURN n",
].join('\n').replace('TYPE','PLAYER');
var params = {
props: data,
};
neo4jClient.query(query, params, function (err, results) {
if(err) return callback(err);
var node = neo4jClient.createNode(results[0].n._data.data);
var player = new Player(node);
node.save(function (err) {
console.dir(err);
if (err) return callback(err);
node.index(INDEX_NAME, INDEX_KEY, INDEX_VAL, function (err) {
if (err) return callback(err);
callback(null, player);
});
});
});
Problem :- Everything goes right but this method creates two nodes in neo4j. I don't know what's happening internally. Please give me some input in this problem.
You actually execute the query which creates the node (and would be good enough).
But then you go again and create a new node node.save() + node.index() both of which are not necessary as the CREATE query already did the work.
It works with following function.
neo4jClient.query(query, params, function (err, results) {
if(err) return callback(err);
var node = results[0].n;
var player = new Player(node);
node.index(INDEX_NAME, INDEX_KEY, INDEX_VAL, function (err) {
if (err) return callback(err);
console.log("=============================");
callback(null, player);
});
});
neo4jClient.query itself create a node so if you call function createNode again then it also create second node. So if you remove createNode function then .query function create a node and also persistent in database as well as in nodejs.
Related
I send two query sequentially
Query the data from A tables, and then accoring to the result, query the data from B table.
So, I query the data like that,
var async = require('async');
var mysql = require('mysql');
var config = require('./config.json');
var connection = mysql.createConnection({
host : config.dbhost,
user : config.dbuser,
password : config.dbpassword,
database : config.dbname
});
exports.handler = (event, context, callback) => {
// TODO implement
var tasks = [
function (callback) {
connection.query("SELECT email FROM Visitor WHERE id =?;", [1], function (err, row) {
if (err) return callback(err);
if (row.length == 0) return callback('No Result Error');
callback(null, row[0]);
})
},
function (data, callback) {
connection.query("SELECT id,signtime FROM Board WHERE email =?;", data.email, function (err, row) {
if (err) return callback(err);
if (row.length == 0) {
return callback('No Result Error');
}else {
callback(null, row[0])
}
})
}
];
async.waterfall(tasks, function (err, result) {
if (err)
console.log('err');
else
***return result;***
console.log('done');
connection.end();
});
};
I log the data with console.log(), it take the data in command line.
But in lambda, put the function into exports.handler, it response null.
If I change the 'return result' to callback(result), it occurs error.
I think it maybe too simple to solve this problem
If you know about that, please help me
In the first case, response is null because you didn't use neither Promise, nor callback to let the Lambda sandbox know that the job is done. In the second case, you used the callback, but you passed the result as the first argument to it. Lambda programming model for Node.js follows a principle called "error first callback". Long story short, if any error occurred during execution, you should go with callback(error), and if everything is ok and you need to return some result from lambda, you should go with callback(null, result). So basically on your line before console.log('done'); use callback(null, result) and it will work for you.
First off, don't worry, it's a tiny data set - I realise it wouldn't be wise to dump an entire production DB to a single screen via an API... I just need to get a JSON dump of entire (small) DB to return via an API endpoint in a Node.js application.
My application does successfully return single records with this code:
MongoClient.connect("mongodb://localhost:27017/search", function (err, db) {
if(err) throw err;
db.collection('results', function(err, collection) {
// search for match that "begins with" searchterm
collection.findOne({'string':new RegExp('^' + searchterm, 'i')}, function(err, items){
// get result
var result;
if (items == null || items.result == null){
result = "";
}
else {
result = items.result;
}
// return result
res.send(result);
});
});
});
So I know Node is talking to Mongo successfully, but how can I tweak this query/code to basically return what you get when you execute the following on the MongoDB command line:
$ db.results.find()
This is snippet.
model.find({}).exec(function (err, result) {
if (err) {console.error(err); return;}
else return result;
});
First use your predefined model and call find. the logic is to place a empty object {} essentially rendering . select all from this model.
Make sense?
Exactly as you've described it.
collection.find({}).exec((err, result) => {
if (err) {
console.log(err);
return;
}
if (result.length > 0) {
// We check that the length is > 0 because using .find() will always
// return an array, even an empty one. So just checking if it exists
// will yield a false positive
res.send(result);
// Could also just use `return result;`
});
Thanks guys, I appreciate your answers pointing me in the right direction, in terms of using {} as the query. Here is the code that eventually worked for me:
db.collection('results', function(err, collection) {
collection.find({}).toArray(function(err, docs) {
res.send(docs);
});
});
The crucial element being the toArray(...) part.
I am new to node and I have read the data from mongoDB successfully.
But I would like to store the whole data from the Collection into a variable in nodejs as I would like to use them in the index page.
I do not know how to store it.
// Connection URL
var url = 'mongodb://localhost:27017/test';
// Use connect method to connect to the Server
MongoClient.connect(url, function (err, db) {
assert.equal(null, err);
console.log("Connected correctly to server");
seriescollection = db.collection('series');
});
var findseries = function (db, callback) {
var cursor = db.collection('series').find();
cursor.each(function (err, doc) {
assert.equal(err, null);
if (doc != null) {
console.dir(doc);
} else {
callback();
}
});
};
MongoClient.connect(url, function (err, db) {
assert.equal(null, err);
//insertDocument(db, function () {});
findseries(db, function () {
db.close();
});
});
My sample JSON object in MongoDb is
{
"_id" : "b835225ba18",
"title" : "Name",
"imageurl" :"https://promotions.bellaliant.net/files/Images/TMN/Ballers-June2015.jpg",
"namespaceId" : "UNI890"
}
I would like to access all the fields and create a page based on the fields that I have stored. I need to access all the fields and that is my main goal.
This is a pet project I am working on a leisure time to learn MEAN stack a bit.
Thanks a lot for your help!!!!
There's a few issues with this code, but I think what you're looking for is the toArray method:
var findseries = function (db, callback) {
db.collection('series').find().toArray(function(err, allTheThings) {
// Do whatever with the array
// Spit them all out to console
console.log(allTheThings);
// Get the first one
allTheThings[0];
// Iterate over them
allTheThings.forEach(function(thing) {
// This is a single instance of thing
thing;
});
// Return them
callback(null, allTheThings);
}
}
More here: https://docs.mongodb.org/manual/reference/method/cursor.toArray/
And here: https://mongodb.github.io/node-mongodb-native/api-generated/cursor.html#toarray
I'm trying to export one function this way:
exports.query = function(request){
conn.query(request, function(err, rows, fields){
if(err) console.log(err);
return rows[0].id;
});
}
and using it:
var mysql = require('./mysql');
console.log(mysql.query('SELECT * FROM tablename'));
Proceeding this way for getting a result involves undefined as output.
How do I to fix this, please?
Note that when I just type console.log(rows[0].id) instead of return rows[0].id it sends back 123.
Thanks in advance!
In your example, the output is being returned to the anonymous function of the database query instead of the caller of the module. You can use a callback to return output to the caller of the module.
exports.query = function(request, callback){
conn.query(request, function(err, rows, fields){
if (err) {
callback(err);
} else {
callback(null, rows[0].id);
}
});
}
Then call it like
var mysql = require('./mysql');
mysql.query('SELECT * FROM tablename', function(err, results){
if (err) {
console.error(err);
} else {
console.log(results);
}
});
That's a problem of synchrony.
the conn.query function returns undefined because it finish its execution before the results are fetched (like almost any i/o related operation on js/node).
One possible solution to that, is to provide a callback to your query function.
exports.query = function(request, cb){
conn.query(request, function(err, rows, fields){
// some "special" processing
cb(err, rows, fields);
});
};
If you're not familiar with async functions, take a look on some articles about that:
http://justinklemm.com/node-js-async-tutorial/
https://www.promisejs.org/
thanks for your help...struggling big time with how to handle this properly. I'm in async now, having given up on my ability to write the callbacks properly. I have snippet where I'm passing a set of random numbers (eachrecord) and passing them through to a mongoose call. Trying to create a data set from the multiple queries I pass.
My issue is that no matter what I've done for 4 hours, the "newarray" variable is always empty.
Thank you for your help -
async.forEach(arLimit, function(eachrecord, callback){
newarray = new Array;
var query = UGC_DB_Model.find({}).skip(eachrecord).limit(-1);
query.execFind(function (err, data) {
if (err)
console.log(err);
else {
newarray.push(data);
}
});
callback(null, newarray);
}, function(err, result) {
if (err) return next(err);
console.log("(it's empty): " + result);
});
There are several issues with your code:
async.forEach isn't meant to 'generate' results, that's what async.map is for;
you need to call the callback only when execFind is done, and not immediately after calling it;
your newarray is probably not necessary;
So try this instead:
async.map(arLimit, function(eachrecord, callback){
var query = UGC_DB_Model.find({}).skip(eachrecord).limit(-1);
query.execFind(function (err, data) {
if (err)
callback(err); // pass error along
else {
callback(null, [ data ]);
// although I think you mean this (because 'data' is probably an array already)
// callback(null, data);
}
});
}, function(err, result) {
if (err) return next(err);
console.log("(it's empty): " + result);
});