count
Description
returns the total number of documents in a collection by using the MongoDB® C++ interface connection.n
= count(conn
,collection
)
returns the total number of documents in an executed MongoDB query on a collection.n
= count(conn
,collection
,Query=mongoquery
)
Examples
Count Documents in Collection
Connect to MongoDB® using the MongoDB C++ interface and count the total number of documents in a collection.
Create a MongoDB connection to the database mongotest
using the MongoDB C++ interface. Here, the database server dbtb01
hosts this database using port number 27017
.
server = "dbtb01"; port = 27017; dbname = "mongotest"; conn = mongoc(server,port,dbname)
conn = connection with properties:
Database: "mongotest"
UserName: ""
Server: "dbtb01"
Port: 27017
CollectionNames: [13×1 string]
conn
is the connection
object that contains the MongoDB connection. The object properties contain information about the connection and the database.
The database name is
mongotest
.The user name is blank.
The database server is
dbtb01
.The port number is
27017
.This database contains 13 document collections.
Verify the MongoDB connection.
isopen(conn)
ans = logical
1
The database connection is successful because the isopen
function returns 1. Otherwise, the database connection is closed.
Determine the number of documents in the employees
collection. The collection contains seven documents.
collection = "employees";
n = count(conn,collection)
n = int64
7
Close the MongoDB connection.
close(conn)
Count Documents in MongoDB Query
Connect to MongoDB® using the MongoDB C++ interface and count the total number of documents in a MongoDB query on a collection in the database. Here, each document in the collection represents an employee.
Create a MongoDB connection to the database mongotest
using the MongoDB C++ interface. Here, the database server dbtb01
hosts this database using port number 27017
.
server = "dbtb01"; port = 27017; dbname = "mongotest"; conn = mongoc(server,port,dbname)
conn = connection with properties:
Database: "mongotest"
UserName: ""
Server: "dbtb01"
Port: 27017
CollectionNames: [13×1 string]
conn
is the connection
object that contains the MongoDB connection. The object properties contain information about the connection and the database.
The database name is
mongotest
.The user name is blank.
The database server is
dbtb01
.The port number is
27017
.This database contains 13 document collections.
Verify the MongoDB connection.
isopen(conn)
ans = logical
1
The database connection is successful because the isopen
function returns 1. Otherwise, the database connection is closed.
Create a JSON-style query as a string scalar that contains a JSON-style string. This query sets the department identifier field equal to 80
.
mongoquery = "{""department_id"":80}";
Use the MongoDB query on the employees
collection to count the total number of employees who work in the specified department. A total of four employees work in the department.
collection = "employees";
n = count(conn,collection,Query=mongoquery)
n = int64
4
Close the MongoDB connection.
close(conn)
Input Arguments
conn
— MongoDB C++ interface connection
connection
object
MongoDB C++ interface connection, specified as a connection
object.
collection
— Collection name
string scalar
Collection name, specified as a string scalar.
Example: "taxidata"
Data Types: string
mongoquery
— MongoDB query
string scalar | character vector
MongoDB query, specified as a string scalar or character vector. Specify a JSON-style string to query the database.
Example: "{""department"":""Sales""}"
queries the database for documents
where the department
field is equal to
Sales
.
Example: "{""salary"": {""$gt"": 90000}}"
queries the database for documents
where the value of the salary
field is
greater than 90000
.
Data Types: string
| char
Output Arguments
n
— Total number of documents
int64
scalar
Total number of documents in a MongoDB collection or query, returned as an int64
scalar.
Version History
Introduced in R2021b
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