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The $addToSet operator adds a value to an array unless the value is already present, in which case $addToSet does nothing to that array.Let us first create a collection with documents −> db.demo380.insertOne({ ... ... "details" : [ ... { ... "Name" : "Chris", ... "details1" : [ ] ... }, ... { ... "Name" : "David", ... "details1" : [ ] ... } ... ] ... } ... ); ... Read More
For projection on specific nested properties, use aggregate() in MongoDB. Let us first create a collection with documents −> db.demo379.insertOne( ... { ... "details1" : { ... "details2" : { ... "details3" : { ... "10" : "John", ... "50" : "Chris", ... "40" : "David", ... "30":"Mike" ... } ... ... Read More
To manipulate subdocuments, use dot(.) notation in MongoDB. Let us first create a collection with documents −> db.demo378.insertOne( ... { ... Name: 'Chris', ... details:[ ... {id:101, Score:56}, ... {id:102, Score:78} ... ] ... } ... ); { "acknowledged" : true, "insertedId" : ObjectId("5e5a758a2ae06a1609a00b0f") }Display all documents from a collection with the help of find() method −> db.demo378.find();This will produce the following output −{ "_id" : ObjectId("5e5a758a2ae06a1609a00b0f"), "Name" : "Chris", "details" : [ { "id" ... Read More
To concatenate, use $concat in MongoDB aggregate(). Let us first create a collection with documents −> db.demo377.insertOne({"ListOfIds":[1001, 1002, 1003, 1004, 1005, 1006, 1007]}); { "acknowledged" : true, "insertedId" : ObjectId("5e5a73462ae06a1609a00b0e") }Display all documents from a collection with the help of find() method −> db.demo377.find().pretty();This will produce the following output −{ "_id" : ObjectId("5e5a73462ae06a1609a00b0e"), "ListOfIds" : [ 1001, 1002, 1003, 1004, 1005, 1006, 1007 ] }Following is the query to concatenate an array of integer ... Read More
To update documents, you cannot use aggregation pipeline. You can use update(). Let us first create a collection with documents −> db.demo376.insertOne( ... { ... ... "id" :101, ... ... "details" : [ ... { ... Name:"Chris", ... Age:21, ... Score:45 ... }, ... { ... Name:"David", ... Age:23, ... ... Read More
JavaScript function can be saved for reuse using a system collection called system.js. To store a function, use the db.collection.save(),Let us first create a function. Following is the query −> db.system.js.save({ ... _id: "displayMessage", ... value: function (data) { ... return 'The Name is: ' + data; ... } ... })This will produce the following output −WriteResult({ "nMatched" : 0, "nUpserted" : 1, "nModified" : 0, "_id" : "displayMessage" })Following is the query to execute stored function −> db.eval("displayMessage('John')") WARNING: db.eval is deprecatedThis will produce the following output −The Name is: John
There is no difference between show dbs and show databases. Both commands internally call listDatabases command.The show dbs command is as follows −> show dbsThis will produce the following output −admin 0.002GB app 0.000GB business 0.000GB config 0.000GB local 0.000GB main 0.000GB ... Read More
To find when the keys are unknown, use $addField and $objectToArray. Let us first create a collection with documents −> db.demo375.insertOne( ... { ... "details":{ ... "Name":"John", ... "Age":23 ... } ... } ... ); { "acknowledged" : true, "insertedId" : ObjectId("5e5a0ae42ae06a1609a00b06") } > db.demo375.insertOne( ... { ... "details":{ ... "Name":"David", ... "Age":21 ... } ... } ... ); { "acknowledged" : true, "insertedId" ... Read More
To group by another field, use $group along with $project. Let us first create a collection with documents −> db.demo374.insertOne( ... { ... ... "Name" : "Chris", ... "HobbyDetails" : [ ... "Reading Book", ... "Playing Football" ... ], ... "CountryName" : "US" ... } ... ); { "acknowledged" : true, "insertedId" : ObjectId("5e5a04402ae06a1609a00b04") } > db.demo374.insertOne( ... { ... ... "Name" : "Chris", ... "HobbyDetails" : [ ... ... Read More
Let us first create a collection with documents −> db.demo373.createIndex({"Name":1, "CountryName":1}); { "createdCollectionAutomatically" : true, "numIndexesBefore" : 1, "numIndexesAfter" : 2, "ok" : 1 } > db.demo373.insertOne({"Name":"Chris", "Age":22, "CountryName":"US"}); { "acknowledged" : true, "insertedId" : ObjectId("5e59ffde2ae06a1609a00aff") } > db.demo373.insertOne({"Name":"David", "Age":21, "CountryName":"AUS"}); { "acknowledged" : true, "insertedId" : ObjectId("5e59ffe82ae06a1609a00b00") } > db.demo373.insertOne({"Name":"Bob", "Age":23, "CountryName":"UK"}); { "acknowledged" : true, "insertedId" : ObjectId("5e59fff42ae06a1609a00b01") } > db.demo373.insertOne({"Name":"John", "Age":21, "CountryName":"US"}); { "acknowledged" : true, "insertedId" : ObjectId("5e59ffff2ae06a1609a00b02") } > db.demo373.insertOne({"Name":"Carol", "Age":23, "CountryName":"AUS"}); { "acknowledged" : true, "insertedId" : ObjectId("5e5a00082ae06a1609a00b03") }Display all ... Read More