Common Mongo Snippets

commonMongo_1.js

// Some data
{ "_id" : 4, "grades" : [ { grade: 80, mean: 75, std: 8 },
                          { grade: 85, mean: 90, std: 5 },
                          { grade: 90, mean: 85, std: 3 } ] }

// Update records based on multiple field matches
db.studenst.update(
    grades: {
        $elemMatch: {
            'grade': {
                $lte: 90
            },
            'mean': {
                $gt: 80
            }
        }
    },
    {
        $set: {
            'grades.$.std': 6
        }
    })

// Add multiple items to an array
db.inventory.update(
                    { _id: 2 },
                    { $addToSet: { tags: { $each: [ "camera",
                                                    "electronics",
                                                    "accessories" ] } } })
                                                    
// Array Update Operators
//http://docs.mongodb.org/manual/reference/operator/update-array/

// Update parameters
db.collection.update(
   <query>,
   <update>,
   {
     upsert: <boolean>,
     multi: <boolean>,
     writeConcern: <document>
   }
)

// Update specific fields
db.books.update(
   { item: "Divine Comedy" },
   {
      $set: { 
          price: 18 ,
          "isbn.publisher": 2222
      },
      $inc: { stock: 5 }
   })
   
// Remove Field
db.books.update( { _id: 11 }, { $unset: { stock: 1 } } )

db.collection.find( {arrayName : {$exists:true}, $where:'this.arrayName.length>1'} )

var query = Query.EQ("author", "Ernest Hemingway");
var cursor = books.Find(query);
foreach (var book in cursor) {
    // do something with book
}

var firstBook = cursor.FirstOrDefault();

foreach (var task in tasks.Find(query).SetSkip(100).SetLimit(10)) {
    // do something with task
}

// Return specified fields
db.inventory.find( { type: 'food' }, { item: 1, qty: 1 } )

// Get a collection
db.collection([[name[, options]], callback);

// Working with ObjectIds, making readable and stringifying
ObjectId(entity._id).toString();

// Insert entity/entities (With lookup values, after inserting, you could lookup
// the values and then you will have the latest from db after inserting)
collection.insert(arrToAdd, function (err, writeConcern) {
  if (err) throw err;
  
  // WriteConcern gives you n statistics on what was inserted, etc...
})

// Add to array only if it DOESN'T exist
{
  $addToSet: {
    tags: ['awesome']
  }
}

// Add to multiple to array only if it DOESN'T exist
{
  $addToSet: {
    tags: {
      $each: ['awesome', 'priority']
    }
  }
}

// Using toArray
collection.find({}, {}).toArray(function (err, docs) {
  // Do something with docs
});

// Remove all items that equals a specified value
collection.update({}, {
    $pull: {
        tags: ['priority']
    }
})

// Query if at least one element exists in an array
db.person.find({
  'aliases.1' : {
    $exists: true
  }
})

// Query if at least one elment exists in an array (ineffecient method)
db.person.find({
  $where: {
    'this.aliases.length': {
      $gt: 0
    }
  }
})