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Articles by Nishtha Thakur
Page 18 of 40
MongoDB find() to operate on recursive search?
Use find() with dot notation to perform recursive search. Let us first create a collection with documents −> db.findOperationDemo.insertOne({"ClientDetails":[{"ClientId":101, "ClientName":"Chris"}, {"ClientId":102, "ClientName":"Robert"}]}); { "acknowledged" : true, "insertedId" : ObjectId("5cd9a118b50a6c6dd317ad99") } > db.findOperationDemo.insertOne({"ClientDetails":[{"ClientId":110, "ClientName":"David"}, {"ClientId":112, "ClientName":"Mike"}]}); { "acknowledged" : true, "insertedId" : ObjectId("5cd9a12fb50a6c6dd317ad9a") }Following is the query to display all documents from a collection with the help of find() method −> db.findOperationDemo.find().pretty();This will produce the following output −{ "_id" : ObjectId("5cd9a118b50a6c6dd317ad99"), "ClientDetails" : [ { "ClientId" : 101, "ClientName" : "Chris" ...
Read MoreMongoDB query to count the size of an array distinctly?
Use DISTINCT for distinct elements and then length to get the size of array −db.yourCollectionName.distinct('yourFieldName').length;Let us first create a collection with documents −> db.countOrSizeDemo.insertOne({"StudentFirstName":"John"}); { "acknowledged" : true, "insertedId" : ObjectId("5cd304f5b64f4b851c3a13dc") } > db.countOrSizeDemo.insertOne({"StudentFirstName":"David"}); { "acknowledged" : true, "insertedId" : ObjectId("5cd304fab64f4b851c3a13dd") } > db.countOrSizeDemo.insertOne({"StudentFirstName":"David"}); { "acknowledged" : true, "insertedId" : ObjectId("5cd304fcb64f4b851c3a13de") } > db.countOrSizeDemo.insertOne({"StudentFirstName":"Carol"}); { "acknowledged" : true, "insertedId" : ObjectId("5cd30500b64f4b851c3a13df") } > db.countOrSizeDemo.insertOne({"StudentFirstName":"Sam"}); { "acknowledged" : true, "insertedId" : ObjectId("5cd30505b64f4b851c3a13e0") } > db.countOrSizeDemo.insertOne({"StudentFirstName":"John"}); { "acknowledged" : true, "insertedId" : ObjectId("5cd3050ab64f4b851c3a13e1") }Following is the query to display all ...
Read MoreHygienic Macros in C
Here we will see the Hygienic Macros in C. We know the usage of macros in C. But sometimes, it does not return the desired results because of accidental capture of identifiers.If we see the following code, we can see that it is not working properly.Example#include #define INCREMENT(i) do { int a = 0; ++i; } while(0) main(void) { int a = 10, b = 20; //Call the macros two times for a and b INCREMENT(a); INCREMENT(b); printf("a = %d, b = %d", a, b); }After preprocessing the code will be like this −Example#include #define ...
Read MoreIs there a way to limit the number of records in a certain MongoDB collection?
Yes, you can use capped parameter along with max size. Following is the syntax −db.createCollection("yourCollectionName", {capped:true, size:yourSizeInBytes, max:howManyRecordsYouWant})Let us first create a collection with capped:true −> db.createCollection("limitTheNumberOfRecordsDemo", {capped:true, size:200024, max:3}) { "ok" : 1 }We will now create a collection with documents −> db.limitTheNumberOfRecordsDemo.insertOne({"ClientName":"James Brown"}); { "acknowledged" : true, "insertedId" : ObjectId("5cd9e601b50a6c6dd317adad") } > db.limitTheNumberOfRecordsDemo.insertOne({"ClientName":"Sam Williams"}); { "acknowledged" : true, "insertedId" : ObjectId("5cd9e60bb50a6c6dd317adae") } > db.limitTheNumberOfRecordsDemo.insertOne({"ClientName":"David Miller"}); { "acknowledged" : true, "insertedId" : ObjectId("5cd9e612b50a6c6dd317adaf") } > db.limitTheNumberOfRecordsDemo.insertOne({"ClientName":"Carol Taylor"}); { "acknowledged" : true, "insertedId" : ObjectId("5cd9e61ab50a6c6dd317adb0") } > db.limitTheNumberOfRecordsDemo.insertOne({"ClientName":"Adam Smith"}); { "acknowledged" ...
Read MorePrint numbers in sequence using thread synchronization
Here we will see how to print numbers in a correct sequence using different threads. Here we will create n number of threads, then synchronize them. The idea is, the first thread will print 1, then second thread will print 2 and so on. When one thread is trying to print, it will lock the resource, so no thread can use that portion.Example#include #include #include #include pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER; pthread_cond_t* cond = NULL; int threads; volatile int count = 0; void* sync_thread(void* num) { //this function is used to synchronize the threads int thread_number ...
Read MoreHow to keep two “columns” in MongoDB unique?
Use unique and set it to TRUE. Let us implement the same by creating index and setting two columns to unique −>db.keepTwoColumnsUniqueDemo.createIndex({"StudentFirstName":1, "StudentLastName":1}, {unique:true}); { "createdCollectionAutomatically" : true, "numIndexesBefore" : 1, "numIndexesAfter" : 2, "ok" : 1 }Now you can insert documents in the above collection −>db.keepTwoColumnsUniqueDemo.insertOne({"StudentFirstName":"John", "StudentLastName":"Smith", "StudentAge":21}); { "acknowledged" : true, "insertedId" : ObjectId("5cd30fd7b64f4b851c3a13e5") } >db.keepTwoColumnsUniqueDemo.insertOne({"StudentFirstName":"John", "StudentLastName":"Doe", "StudentAge":23}); { "acknowledged" : true, "insertedId" : ObjectId("5cd30fe5b64f4b851c3a13e6") } >db.keepTwoColumnsUniqueDemo.insertOne({"StudentFirstName":"John", "StudentLastName":"Smith", "StudentAge":24}); 2019-05-08T22:50:42.803+0530 E QUERY [js] WriteError: E11000 duplicate key error collection: sample.keepTwoColumnsUniqueDemo index: StudentFirstName_1_StudentLastName_1 dup key: { : "John", : "Smith" } ...
Read MoreFind a strict document that contains only a specific field with a fixed length?\\n
You can use $where operator for this. Let us first create a collection with documents −>db.veryStrictDocumentDemo.insertOne({"StudentFirstName":"John", "StudentLastName":"Doe", "StudentAge":23}); { "acknowledged" : true, "insertedId" : ObjectId("5cda4bcdb50a6c6dd317adb8") } > db.veryStrictDocumentDemo.insertOne({"StudentFirstName":"Larry"}); { "acknowledged" : true, "insertedId" : ObjectId("5cda4bdbb50a6c6dd317adb9") } >db.veryStrictDocumentDemo.insertOne({"StudentFirstName":"David", "StudentLastName":"Miller"}); { "acknowledged" : true, "insertedId" : ObjectId("5cda4becb50a6c6dd317adba") } > db.veryStrictDocumentDemo.insertOne({"StudentFirstName":"Chris"}); { "acknowledged" : true, "insertedId" : ObjectId("5cda4bfbb50a6c6dd317adbb") } > db.veryStrictDocumentDemo.insertOne({"StudentFirstName":"Bob", "StudentLastName":"Brown"}); { "acknowledged" : true, "insertedId" : ObjectId("5cda4c6db50a6c6dd317adbc") }Following is the query to display all documents from a collection with the help of find() method −> db.veryStrictDocumentDemo.find();This will produce the following output ...
Read MoreProgram for Christmas Tree in C
Here we will see one interesting problem. In this problem, we will see how to print Christmas tree randomly. So the tree will be flickering like Christmas tree lights.To print a Christmas tree, we will print pyramids of various sizes just one beneath another. For the decorative leaves a random character is printed from a given list of characters. The height and randomness is adjustable.Here after generating a tree, the whole screen is cleared, then generate again, that’s why this is looking like flickering tree.Example#include #include #include #include #define REFRESH_RATE 40000 #define RANDOM_NESS 5 // The ...
Read MoreProject specific array field in a MongoDB collection?
Let us first create a collection with documents −> db.projectionAnElementDemo.insertOne( ... { ... "CustomerId":100, ... "CustomerDetails": [ ... { ... "CustomerName": "Chris", ... "CustomerCountryName": "US" ... }, ... { ... "CustomerName": "Robert", ... "CustomerCountryName": "UK" ... } ... ] ... } ... ); { "acknowledged" : true, ...
Read Moreabs(), labs(), llabs() functions in C/C++
In the cstdlib library of C++, there are different functions for getting the absolute value except from abs. The abs are used basically for int type input in C, and int, long, long long in C++. The others are used for long, and long long type data etc. Let us see the usage of these functions.The abs() FunctionThis function is used for int type data. So this returns the absolute value of the given argument. The syntax is like below.int abs(int argument)Example#include #include #include using namespace std; main() { int x = -145; int y = 145; cout
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