Is there a way to monitor changes in the alphabetical order of a field in mongodb?

Question

Is there a way to monitor changes in the alphabetical order of a field in mongodb?

Imagine I have a file in my mongo database with various documents stored in the CARS collection.

If I want to sort them, I can use:

db.cars.find().sort({car:1, price:-1})

Now, I am looking for a query that will return the top car of each category based on 'car'. Specifically, I would like to add a new field called "price_high" to these selections using

{$set:{"price_high"},{multi:true}}

.

'car':Chevy, 'price':100 //This is the top one from Chevy
'car':Chevy, 'price': 80 
'car':Chevy, 'price': 60 
'car':Lexus, 'price':99 //Top Lexus
'car':Lexus, 'price':90 
'car':Lexus, 'price':85 
'car':Maserati, 'price':99 //Top Maserati
'car':Maserati, 'price':96 
'car':Maserati, 'price':93

This query should be executed only in the MONGO TERMINAL, not written into a file!

javascript arrays json mongodb

Answer 1

Answer №1

If you're delving into MongoDB for the first time, what you need to familiarize yourself with is the .aggregate() method. This function in MongoDB serves a similar purpose to "GROUP BY" in SQL and allows for various data manipulation operations.

To retrieve results and make updates to the data, you can use a process similar to this (preferably in bulk):

var bulk = db.collection.initializeOrderedBulkOp(),
    count = 0;

db.collection.aggregate([
    // Arrange data as needed
    { "$sort": { "car": 1, "price": -1 } },

    // Group by the initial entries for each car
    { "$group": {
        "_id": "$car",
        "doc_id": { "$first": "$_id" },
        "price": { "$first": "$price" }
    }}
]).forEach(function(doc) {
    bulk.find({ "_id": doc.doc_id }).updateOne({
        "$set": { "price_high": true }
    });
    count++;

    // Clear every 1000 processed and restart
    if ( count % 1000 == 0 ) {
       bulk.execute();
       bulk = db.collection.initializeOrderedBulkOp();
    }
});

// Process any remaining records
if ( count % 1000 != 0 )
    bulk.execute();

In cases where you have a small set of real samples, it may be more efficient to extract the necessary _id values and utilize $in with {multi:true} in your update query.

The core concept here is to employ .aggregate() to fetch the top documents (utilizing $first after $sort is crucial) and then execute the necessary actions to update the obtained results.

Answer 2

If you're delving into MongoDB for the first time, what you need to familiarize yourself with is the .aggregate() method. This function in MongoDB serves a similar purpose to "GROUP BY" in SQL and allows for various data manipulation operations.

To retrieve results and make updates to the data, you can use a process similar to this (preferably in bulk):

var bulk = db.collection.initializeOrderedBulkOp(),
    count = 0;

db.collection.aggregate([
    // Arrange data as needed
    { "$sort": { "car": 1, "price": -1 } },

    // Group by the initial entries for each car
    { "$group": {
        "_id": "$car",
        "doc_id": { "$first": "$_id" },
        "price": { "$first": "$price" }
    }}
]).forEach(function(doc) {
    bulk.find({ "_id": doc.doc_id }).updateOne({
        "$set": { "price_high": true }
    });
    count++;

    // Clear every 1000 processed and restart
    if ( count % 1000 == 0 ) {
       bulk.execute();
       bulk = db.collection.initializeOrderedBulkOp();
    }
});

// Process any remaining records
if ( count % 1000 != 0 )
    bulk.execute();

In cases where you have a small set of real samples, it may be more efficient to extract the necessary _id values and utilize $in with {multi:true} in your update query.

The core concept here is to employ .aggregate() to fetch the top documents (utilizing $first after $sort is crucial) and then execute the necessary actions to update the obtained results.

Answer 3

Answer №2

If you want to retrieve the highest prices for each car from a collection using the group aggregate function:

db.cars.aggregate(
[
{$group:
  {
  "_id": "$car",
  "price":{"$max":"$price"},
  "gid":{"$first":"$_id"}
  }
 }
 ]
  ).forEach(function(doc)
   {
   db.cars.update({"_id":doc.gid,"car":doc._id,"price":doc.price},
   {"$set":{"price_high" : true}});
 }

Answer 4

If you want to retrieve the highest prices for each car from a collection using the group aggregate function:

db.cars.aggregate(
[
{$group:
  {
  "_id": "$car",
  "price":{"$max":"$price"},
  "gid":{"$first":"$_id"}
  }
 }
 ]
  ).forEach(function(doc)
   {
   db.cars.update({"_id":doc.gid,"car":doc._id,"price":doc.price},
   {"$set":{"price_high" : true}});
 }

Is there a way to monitor changes in the alphabetical order of a field in mongodb?

Answer №1

Answer №2

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