CODEWITHSUNDEEP
node.jsmongodbmongoose
Faizuddin Mohammed
Faizuddin Mohammed

Reputation: 4328

How do I modify the output of a Mongoose query?

I have a field in my MongoDB collection products called date_expired.

It's of type: date and stores the a date string.

I want to retrieve all the products and change the date_expired property in the result to number of hours left from now. How do I do this?

It's similar to getter() in Laravel...?

Upvotes: 1

Views: 1556

Answers (2)

robertklep
robertklep

Reputation: 203304

You could create a virtual property that will return the number of hours until expiry:

ProductSchema.virtual('hoursToExpiry').get(function() {
  return (this.date_expired - Date.now()) / 3600000;
});

To access this property:

console.log('hours to expiry:', doc.hoursToExpiry)

If you want to include that property in any JSON or JS object, make sure that you set virtuals : true:

console.log('%j', doc.toJSON({ virtuals : true }));

Upvotes: 3

chridam
chridam

Reputation: 103365

Would consider using the aggregation framework in this case to output the transformation. You can use the $project pipeline arithmetic operators $divide and $subtract to achieve the final goal. These will enable you to carry out the arithmetic of calculating the number of hours to expiry i.e. implement the formula:

hoursToExpiry = (date_expired - timeNow)/1000*60*60 //the time units are all in milliseconds

Take for instance the following short mongo shell demo that will strive to drive home this concept:

Populate test collection:

db.test.insert([
    {
        "date_expired": ISODate("2016-03-27T10:55:13.069Z"),
        "name": "foo"
    },
    {
        "date_expired": ISODate("2016-06-11T20:55:13.069Z"),
        "name": "bar"
    },
    {
        "date_expired": ISODate("2016-06-11T16:17:23.069Z"),
        "name": "buzz"
    }
])

Aggregation Operation:

db.test.aggregate([
    { 
        "$project": { 
            "name": 1,  
            "dateExpired": "$date_expired",
            "dateNow": { "$literal": new Date() },
            "hoursToExpiry": { 
                "$divide": [
                    { "$subtract": [ "$date_expired", new Date() ] }, 
                    1000*60*60
                ] 
            }
         }
    }
])

Result (at the time of writing):

{
    "result" : [ 
        {
            "_id" : ObjectId("575c0f6e8101b29fc93e5b9d"),
            "name" : "foo",
            "dateExpired" : ISODate("2016-03-27T10:55:13.069Z"),
            "dateNow" : ISODate("2016-06-11T13:36:21.025Z"),
            "hoursToExpiry" : -1826.685543333333
        }, 
        {
            "_id" : ObjectId("575c0f6e8101b29fc93e5b9e"),
            "name" : "bar",
            "dateExpired" : ISODate("2016-06-11T20:55:13.069Z"),
            "dateNow" : ISODate("2016-06-11T13:36:21.025Z"),
            "hoursToExpiry" : 7.314456666666667
        }, 
        {
            "_id" : ObjectId("575c0f6e8101b29fc93e5b9f"),
            "name" : "buzz",
            "dateExpired" : ISODate("2016-06-11T16:17:23.069Z"),
            "dateNow" : ISODate("2016-06-11T13:36:21.025Z"),
            "hoursToExpiry" : 2.683901111111111
        }
    ],
    "ok" : 1
}

With the above pipeline, you can then adopt it to your Mongoose implementation with the aggregate() method as basis of your query:

Product.aggregate([
    { 
        "$project": { 
            "name": 1,  
            "dateExpired": "$date_expired",
            "dateNow": { "$literal": new Date() },
            "hoursToExpiry": { 
                "$divide": [
                    { "$subtract": [ "$date_expired", new Date() ] }, 
                    1000*60*60
                ] 
            }
         }
    }
]).exec(function (err, result) {
    // Handle err
    console.log(result);
});

or using the more affluent API:

Product.aggregate()
     .project({ 
        "name": 1,  
        "dateExpired": "$date_expired",
        "dateNow": { "$literal": new Date() },
        "hoursToExpiry": { 
            "$divide": [
                { "$subtract": [ "$date_expired", new Date() ] }, 
                1000*60*60
            ] 
        }
    })
    .exec(function (err, result) {
        // Handle err
        console.log(result);
    });

Upvotes: 1

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