Database Articles - Page 127 of 618

For this, use $group along with $max in MongoDB. Let us create a collection with documents −> db.demo510.insertOne( ... { ...    details:[ ...       { ...          Name:"Chris", ...          Score:56 ...       }, ...       { ...          Name:"David", ...          Score:45 ...       } ...    ] ... } ... ); {    "acknowledged" : true,    "insertedId" : ObjectId("5e8845fa987b6e0e9d18f582") } > db.demo510.insertOne( ... { ...    details:[ ...       { ...       ... Read More

For this, use update() along with $addToSet. The $addToSet operator adds value to an array unless the value is already present, in which case $addToSet does nothing to that array. Let us create a collection with documents −> db.demo509.insertOne( ... { ... ...    "value1" : [ ...       { ...          "value2" : [ ...             76, ...             14, ...             56 ...          ] ...       }, ...       { ... Read More

Yes, you can track how many times each index is used in a query using MongoDB $indexStats. Following is the query to create an index in MongoDB −> db.demo508.createIndex({"FirstName":1}); {    "createdCollectionAutomatically" : true,    "numIndexesBefore" : 1,    "numIndexesAfter" : 2,    "ok" : 1 }Let us create a collection with documents −> db.demo508.insertOne({"FirstName":"John"});{    "acknowledged" : true,    "insertedId" : ObjectId("5e883818987b6e0e9d18f578") } > db.demo508.insertOne({"FirstName":"Chris"});{    "acknowledged" : true,    "insertedId" : ObjectId("5e88381b987b6e0e9d18f579") } > db.demo508.insertOne({"FirstName":"David"});{    "acknowledged" : true,    "insertedId" : ObjectId("5e88381f987b6e0e9d18f57a") }Display all documents from a collection with the help of find() method −> db.demo508.find();This will ... Read More

To filter and fetch, use projection along with MongoDB $filter and $match. Let us create a collection with documents −> db.demo507.insertOne( ... { ... ...    "Information": ...    [ ...       {"Name":"John", "SubjectName":"MySQL"}, ...       {"Name":"Bob", "SubjectName":"MongoDB"}, ...       {"Name":"Chris", "SubjectName":"MySQL"}, ...       {"Name":"David", "SubjectName":"C++"} ...    ] ... } ... ); {    "acknowledged" : true,    "insertedId" : ObjectId("5e8836d3987b6e0e9d18f577") }Display all documents from a collection with the help of find() method −> db.demo507.find().pretty();This will produce the following output −{    "_id" : ObjectId("5e8836d3987b6e0e9d18f577"),    "Information" : [     ... Read More

To increment the value of an array object, use $inc. Let us create a collection with documents −>db.demo506.insertOne({"details":[{id:1, Quantity:4}, {id:2, Quantity:3}, {id:3, Quantity:2}, {id:4, Qua ntity:7}]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e882ed6987b6e0e9d18f576") }Display all documents from a collection with the help of find() method −> db.demo506.find().pretty();This will produce the following output −{    "_id" : ObjectId("5e882ed6987b6e0e9d18f576"),    "details" : [       {          "id" : 1,          "Quantity" : 4       },       {          "id" : 2,         ... Read More

To sort nested array in MongoDB, use $sort. Let us create a collection with documents −> db.demo505.insertOne( ... { ...    "details": [ ...    { ...       Name:"Chris", ...       "Score":58 ...    }, { ... ...          Name:"Bob", ...          "Score":45 ...       }, { ... ...             Name:"John", ...             "Score":68 ...       }, { ... ...          Name:"David", ...          "Score":46 ...       } ... Read More

To find the user by name in MongoDB, use find(). Let us create a collection with documents −> db.demo504.insertOne({"Name":"Chris"});{    "acknowledged" : true,    "insertedId" : ObjectId("5e8823ee987b6e0e9d18f570") } > db.demo504.insertOne({"Name":"John"});{    "acknowledged" : true,    "insertedId" : ObjectId("5e8823f2987b6e0e9d18f571") } > db.demo504.insertOne({"Name":"David"});{    "acknowledged" : true,    "insertedId" : ObjectId("5e8823f5987b6e0e9d18f572") }Display all documents from a collection with the help of find() method −> db.demo504.find();This will produce the following output −{ "_id" : ObjectId("5e8823ee987b6e0e9d18f570"), "Name" : "Chris" } { "_id" : ObjectId("5e8823f2987b6e0e9d18f571"), "Name" : "John" } { "_id" : ObjectId("5e8823f5987b6e0e9d18f572"), "Name" : "David" }Following is the query to find a user by ... Read More

To slice array, use a $slice operator in MongoDB. Let us create a collection with documents −> db.demo503.insertOne({_id:1, Name:"John", Subject:["MySQL", "Java", "C"]}); { "acknowledged" : true, "insertedId" : 1 } > db.demo503.insertOne({_id:2, Name:"David", Subject:["MongoDB", "C++", "Python"]}); { "acknowledged" : true, "insertedId" : 2 }Display all documents from a collection with the help of find() method −> db.demo503.find().pretty();This will produce the following output −{ "_id" : 1, "Name" : "John", "Subject" : [ "MySQL", "Java", "C" ] } {    "_id" : 2,    "Name" : "David",    "Subject" : [       "MongoDB",       "C++",     ... Read More

For combination, use $concat and check the equality using $eq. Let us create a collection with documents −> db.demo502.insertOne({"FirstName":"John", "LastName":"Smith"});{    "acknowledged" : true,    "insertedId" : ObjectId("5e875534987b6e0e9d18f56d") } > db.demo502.insertOne({"FirstName":"David", "LastName":"Miller"});{    "acknowledged" : true,    "insertedId" : ObjectId("5e87553e987b6e0e9d18f56e") } > db.demo502.insertOne({"FirstName":"John", "LastName":"Doe"});{    "acknowledged" : true,    "insertedId" : ObjectId("5e875543987b6e0e9d18f56f") }Display all documents from a collection with the help of find() method −> db.demo502.find();This will produce the following output −{ "_id" : ObjectId("5e875534987b6e0e9d18f56d"), "FirstName" : "John", "LastName" : "Smith" } { "_id" : ObjectId("5e87553e987b6e0e9d18f56e"), "FirstName" : "David", "LastName" : "Miller" } { "_id" : ObjectId("5e875543987b6e0e9d18f56f"), "FirstName" : "John", ... Read More

To group duplicate documents, use MongoDB aggregate(). Let us create a collection with documents −> db.demo501.insertOne({"Name":"Chris"});{    "acknowledged" : true,    "insertedId" : ObjectId("5e8752f0987b6e0e9d18f566") } > db.demo501.insertOne({"Name":"Bob"});{    "acknowledged" : true,    "insertedId" : ObjectId("5e8752f4987b6e0e9d18f567") } > db.demo501.insertOne({"Name":"Chris"});{    "acknowledged" : true,    "insertedId" : ObjectId("5e8752f8987b6e0e9d18f568") } > db.demo501.insertOne({"Name":"John"});{    "acknowledged" : true,    "insertedId" : ObjectId("5e8752fb987b6e0e9d18f569") } > db.demo501.insertOne({"Name":"Chris"});{    "acknowledged" : true,    "insertedId" : ObjectId("5e8752fd987b6e0e9d18f56a") } > db.demo501.insertOne({"Name":"John"});{    "acknowledged" : true,    "insertedId" : ObjectId("5e875301987b6e0e9d18f56b") } > db.demo501.insertOne({"Name":"David"});{    "acknowledged" : true,    "insertedId" : ObjectId("5e875307987b6e0e9d18f56c") }Display all documents from a collection with the help of ... Read More