How to work with MongoDB in .NET

Get started with documents and collections in the popular, open source, NoSQL database using C#

MongoDB is a popular, open source, scale-out NoSQL database that provides high throughput for your data-driven applications. Unlike relational databases such as SQL Server, Oracle, and MySQL, which store data in tables according to a rigid schema, MongoDB stores data in documents with flexible schema. There are many such non-relational databases around including CouchDB, RavenDB, and Couchbase. However, I like MongoDB primarily due to its scalability, speed, and dynamic querying capabilities.

MongoDB uses the BSON format under the hood to represent the JSON documents at the heart of the data store. BSON or “Binary JSON” is a lightweight and efficient binary-encoded data serialization format that supports fast data traversal and searches. BSON also allows MongoDB to support data types—namely int, long, date, floating point, and decimal128—not represented in JSON. 

In MongoDB documents are part of collections, in much the same way as a row is part of a table in a relational database. A document is essentially a collection of field and value pairs, which can also be nested. Note that a value in MongoDB can be a document, an array of documents, an array of BSON, or just a BSON type. Let’s look at how we can work with MongoDB using C#. 

Install MongoDB and create a new project

Start by downloading the MongoDB binaries. Unzip the binaries to a folder of your choice in your system and create a separate folder (in my case C:\data\db) for the data. Then, to start MongoDB, navigate to the folder where MongoDB is installed and execute the mongod command in the command prompt window. That should start MongoDB at port 27017 by default.

Create a new console application project in Visual Studio and install the MongoDB.Driver package via the NuGet Package Manager Console with the following command.  

PM> Install-Package MongoDB.Driver

This will install the following three NuGet packages at one go.

• MongoDB.Bson
• MongoDB.Driver.Core
• MongoDB.Driver

Connect to your MongoDB instance

To connect to a MongoDB instance at its default port 27017, you can use the default constructor of the MongoClient class as shown below.

var client = new MongoClient();

Now consider the following class. We will use this class to store data in MongoDB.

public class Author
    {
        public int Id { get; set; }
        public string FirstName { get; set; }
        public string LastName { get; set; }
    }

Create a database and collection

The following code listing shows how you can create a database and a collection inside it and then insert an object inside the collection.

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static void Main(string[] args)
    {           
        var connectionString ="mongodb://localhost:27017";
        var client = new MongoClient(connectionString);           
        IMongoDatabase db = client.GetDatabase(“IDG”);
        Author author = new Author
        {
            Id = 1,
            FirstName ="Joydip",
            LastName ="Kanjilal"
        };
        var collection = db.GetCollection<Author>(“authors”);
        collection.InsertOne(author);
        Console.Read();
    }

Note that the following namespaces should be included in your program.

using MongoDB.Bson;
using MongoDB.Driver;

Now refer to the Main method in the code listing above. Note that the following statement creates new a database named ”IDG” if none exists by that name.

IMongoDatabase db = client.GetDatabase(“IDG”);

Similarly, the following statement creates a new collection of ”Author” objects if none exists. In either case, the GetCollection method returns a collection instance.

var collection = db.GetCollection<Author>(“authors”);

Add documents to the collection

Next, we create an instance of the Author class and assign values to its FirstName and LastName properties.

Author author = new Author
{
    Id = 1,
    FirstName ="Joydip",
    LastName ="Kanjilal"
};

Use the statement below to insert the instance of the Author class into the collection.

collection.InsertOne(author);

Note that you can insert multiple documents all at the same time using the InsertMany or InsertManyAsync method. The following code listing illustrates how the InsertMany method can be used.

using System;
using System.Collections.Generic;
using MongoDB.Bson;
using MongoDB.Driver;

static void Main(string[] args)
    {           
        var connectionString ="mongodb://localhost:27017";
        var client = new MongoClient(connectionString);           
        IMongoDatabase db = client.GetDatabase(“IDG”);
        var collection = db.GetCollection<BsonDocument>(“IDGAuthors”);
        var author1 = new BsonDocument
        {
            {”id”, 1},
            {”firstname”, “Joydip”},
            {”lastname”, “Kanjilal”}
        };
        var author2 = new BsonDocument
        {
            {”id”, 2},
            {”firstname”, “Steve”},
            {”lastname”, “Smith”}
        };
        var author3 = new BsonDocument
        {
            {”id”, 3},
            {”firstname”, “Gary”},
            {”lastname”, “Stevens”}
        };
        var authors = new List<BsonDocument>();
        authors.Add(author1);
        authors.Add(author2);
        authors.Add(author3);
        collection.InsertMany(authors);
        Console.Read();
    }

The BsonDocument class in the MongoDB.Bson package is used to represent a BSON document. The following code snippet shows how you can display the names of the databases available in the instance of MongoDB running in your system.

var connectionString ="mongodb://localhost:27017";
var client = new MongoClient(connectionString);           
    using (var cursor = client.ListDatabases())
    {
        var databaseDocuments = cursor.ToList();
        foreach (var db in databaseDocuments)
        {
            Console.WriteLine(db[“name”].ToString());
        }
    }

When you execute the above code snippet, you will see the name of the database (i.e., “IDG”) listed in the console window. You can also use the asynchronous method, ListDatabasesAsync, to list the database names, as shown in the code snippet given below.

private static async Task DisplayDatabaseNames()
    {
        var connectionString ="mongodb://localhost:27017";
        var client = new MongoClient(connectionString);
        try
        {
            using (var cursor = await client.ListDatabasesAsync())
            {
                await cursor.ForEachAsync(document => Console.WriteLine(document.ToString()));
            }               
        }
        catch
        {
            //Write your own code here to handle exceptions
        }
    }

MongoDB is a popular NoSQL database that has a flexible data model and scales gracefully. MongoDB provides support for horizontal scalability using a technique known as sharding. I will discuss more advanced concepts in MongoDB in future posts here. Until then, you may want to read up on the MongoDB C# driver in the MongoDB documentation. 

[출처] https://www.infoworld.com/article/3224457/how-to-work-with-mongodb-in-dotnet.html