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POHow to process ISO date sting in the MongoDB mapReduce function in Node.js
 

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  1. POHow to process ISO date sting in the MongoDB mapReduce function in Node.js
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    <p>I'm using the Date function in the mapReduce function in the Node.js application. In the map function below, I convert the ISO date string to the Date object first. Then get the year of the date, which will be used as the key. The expected result is the _id in the output collection is "2013". But in fact, the _id is NaN (The type is Double). </p> <p>It seems that the Date function used inside the mapReduce function is different from normal JS Date function. </p> <ol> <li>How can I use the normal JS Date function inside the map function below?</li> <li>If it is impossible, how to process the ISO date string inside the map function?</li> </ol> <p>.</p> <pre><code>var mongodb = require('mongodb'); var map = function() { var date = new Date("2013-03-19T08:27:58.001Z"); // Convert ISO date string to Date object var year = date.getFullYear(); // Get the year of the date. emit(year, this); }; var reduce = function(key, values) { if (values.length) { return values[0]; } }; /**Connect to MongoDB */ var server = new mongodb.Server(dbIP, dbPort, {}); var db = new mongodb.Db(dbName, server, {safe:true}); db.open(function (err, client) { if( err ) { console.log('DB: Failed to connect the database'); } else { console.log('DB: Database is connected'); db.collection(collectionName).mapReduce( map, reduce, { out: 'map_reduce_collection' } , function (err, collection, stats){ if( err ) { console.log('Map reduce: Fail.'); } else { console.log('Map reduce: Success.'); } db.close(); }); } }); </code></pre> <p>=======EDIT: Add the solution=========</p> <p>ISODate solves my issue. The code below works for me.</p> <pre><code>// The map and reduce functions are serialized by the driver and run in the MongoDB server. // The functions used in them should be supported by the mongo shell. // A tip is checking if a function is supported by map-reduce function by execuing it in the mongo shell. // For example, the Date function is different from the one supported by Node.js. // In Node.js, the var date = new Date("2013-03-19T08:27:58.001Z"); works. But it doesn't work in mongo shell. // So it can't be used in the map function. var map = function() { var date = new ISODate("2013-03-19T08:27:58.001Z"); var year = date.getFullYear(); emit(year, this); }; </code></pre> <p>Thanks, Jeffrey</p>
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    1. COWhy don't you exchange the `new Date()` for a `new ISODate()`, the ISODate is basically a more advanced and better wrapper for date so you can use all the same functions.
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    2. COFWIW, the `map` and `reduce` functions are serialized by the driver and run in the MongoDB server, hence the asymmetry.
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    3. COThank you Sammaye. The 'var date = new ISODate("2013-03-19T08:27:58.001Z");' returns the expected date object.
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      1. USJeffrey
 

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