Pass variables to mongodb query in nodejs - node.js

Question

Can I pass a variable to a query so:
db.collection('coll').find(query).toArray(function(err, docs) {
if(err) throw err;
docs.forEach(function(doc) {
var Id = parseInt(doc._id); // a returnd _id from previous query
Id--;
query = {_id : parseInt(doc._id) }; // returns null
// OR query = {_id : Id }; // error
db.collection('coll').find(query).toArray(function(err, beforeDocs) {
//if (err) throw err;
console.dir(beforeDocs);
});
});
In fact what I am trying to do is query by id to get the record that comes before the results given in the first query
Any ideas??
Is it at all possible to query mongodb with variables??
var query = { _id : var i, name : var name , etc...}

Answer 1

There is no way to search for the document that shows up before a match in a mongodb query.
I believe your best bet is something like this:
var prevDoc = null; // to store the previous document
var cursor = db.collection('collection').find({}); // get all docs
cursor.sort('_id', 1); // it only makes sense to grab previous if they're sorted
cursor.each(function(err, doc) {
if(err) throw err;
if(doc == null) { // if we reached the end of our cursor...
db.close(); // close the db connection
} else {
if( doc.foo === "bar" ) { // here you put your match criteria
console.dir(prevDoc); // here you print your previous document
}
}
prevDoc = doc; // store current doc so that it's available for next iteration
});
To answer your direct question ("Is it at all possible to query mongodb with variables?"), it is possible to query mongodb with a query which contains variables that already have values at the time the query is created. It is not possible, however, to pass new uninstantiated variables along for mongodb to manipulate somehow.