How to write multiple queries in a row?
Like a
Space.findOne({ _id: id }, function(err, space) {
User.findOne({ user_id: userid }, function(err, user) {
res.json({ space: space, user: user});
});
});
does not look good with more requests and logic
How is it done correctly?
I heard something about the promise, but I do not know.
Thanks
When I've had a similar issue, I've used the async library.
async.parallel([
function(callback){
Space.findOne({ _id: id }, callback);
},
function(callback){
User.findOne({ user_id: userid },callback);
}
],
function(err, results){
res.json({space:results[0],user:results[1]});
});
You can also use async.series if you want sequential execution.
.bind but I'm avoiding that for clarity.@Benjamin's approach is correct. Mongoose also provides the populate method, which fetches multiple objects that are related to each other by their id. This also happens in parallel and is a special case of multiple queries. See http://mongoosejs.com/docs/populate.html for more examples.
If you're using Node.js 4+ which supports Promises, you can wrap the query in a promise.
queryPromise = function(findQueryCursor) {
return new Promise(function(resolve, reject) {
findQueryCursor.toArray(function(err, data) {
resolve(data);
});
});
};
Then, create an array of Promises consisting of queries:
promiseAr = [];
promiseAr.push(
queryPromise(
db.collection('dbname').find(query1)
)
);
promiseAr.push(
queryPromise(
db.collection('dbname').find(query2)
)
);
Then call
Promise.all(promiseAr)
.then(function(dataArray) {
// results of query1 in dataArray[0]
// results of query2 in dataArray[1]
})
.catch(function(err) {
// catch errors
});
The queries will be sent in parallel to MongoDB, and the ".then" function will be called after all the queries have completed.
The reason you have to do this is because the .find() function returns a cursor, and then you have to call .toArray() to retrieve the data. .toArray() itself is asynchronous, so you have to wrap it in a Promise if you want to use Promise.all.
