MongoDB Driver Quick Tour

This is the first part of the MongoDB driver quick tour. In this part, we will look at how to perform basic CRUD (create, read, update, delete) operations. In the next part, we’ll look at performing some adminstrative functions.

Make a connection

The following example shows three ways to connect to a server or servers on the local machine.

// To directly connect to a single MongoDB server
// (this will not auto-discover the primary even if it's a member of a replica set)
var client = new MongoClient();

// or use a connection string
var client = new MongoClient("mongodb://localhost:27017");

// or, to connect to a replica set, with auto-discovery of the primary, supply a seed list of members
var client = new MongoClient("mongodb://localhost:27017,localhost:27018,localhost:27019");

The client instance now holds a pool of connections to the server or servers specified in the connection string.

MongoClient

The MongoClient instance actually represents a pool of connections to the database; you will only need one instance of class MongoClient even with multiple threads.

Get a Database

To get a database, specify the name of the database to the GetDatabase method on client. It’s ok if the database doesn’t yet exist. It will be created upon first use.

var database = client.GetDatabase("foo");

The database variable now holds a reference to the “foo” database.

Get a Collection

To get a collection to operate upon, specify the name of the collection to the GetCollection<TDocument> method on database. It’s ok if the collection doesn’t yet exist. It will be created upon first use.

var collection = database.GetCollection<BsonDocument>("bar");

The collection variable now holds a reference to the “bar” collection in the “foo” database.

Insert a Document

Once you have the collection instance, you can insert documents into the collection. For example, consider the following JSON document; the document contains a field info which is an embedded document:

{
     "name": "MongoDB",
     "type": "database",
     "count": 1,
     "info": {
         x: 203,
         y: 102
     }
}

To create the document using the .NET driver, use the BsonDocument class. You can use this class to create the embedded document as well.

var document = new BsonDocument
{
    { "name", "MongoDB" },
    { "type", "Database" },
    { "count", 1 },
    { "info", new BsonDocument
              {
                  { "x", 203 },
                  { "y", 102 }
              }}
};

To insert the document into the collection, use the InsertOneAsync method.

await collection.InsertOneAsync(doc);

Insert Multiple Documents

To insert multiple documents, you can use the InsertManyAsync method.

// generate 100 documents with a counter ranging from 0 - 99
var documents = Enumerable.Range(0, 100).Select(i => new BsonDocument("counter", i));

await collection.InsertManyAsync(documents);

Counting Documents

Now that we’ve inserted 101 documents (the 100 we did in the loop, plus the first one), we can check to see if we have them all using the CountAsync method. The following code should print 101.

var count = await collection.CountAsync(new BsonDocument());

Console.WriteLine(count);

Query the Collection

Use the Find method to query the collection. The Find method returns an IFindFluent<TDocument, TProjection> instance that provides a fluent interface for chaining or controlling find operations.

Find the First Document in a Collection

To get the first document in the collection, call the FirstOrDefaultAsync method. await collection.Find(new BsonDocument()).FirstOrDefaultAsync() returns the first document or null. This is useful for queries that should only match a single document, or if you are interested in the first document only.

The following example prints the first document found in the collection.

var document = await collection.Find(new BsonDocument()).FirstOrDefaultAsync();
Console.WriteLine(document.ToString());

The example should print the following document:

{ 
    "_id": ObjectId("551582c558c7b4fbacf16735") },
    "name": "MongoDB", 
    "type": "database", 
    "count": 1,
    "info": { "x" : 203, "y" : 102 } 
}

Find All Documents in a Collection

To retrieve all the documents in the collection, call the ToListAsync method. This is useful when the number of documents expected to be returned is small.

var documents = await collection.Find(new BsonDocument()).ToListAsync();

If the number of documents is expected to be large or they can be processed iteratively, the ForEachAsync will invoke a callback for each document returned.

await collection.Find(new BsonDocument()).ForEachAsync(d => Console.WriteLine(d));

Each of the above examples will print the exact same thing to the console. For more information on iteration, see the reference documention.

Get a Single Document with a Filter

We can create a filter to pass to the Find method to get a subset of the documents in our collection. For example, if we wanted to find the document for which the value of the “i” field is 71, we would do the following:

var filter = Builders<BsonDocument>.Filter.Eq("i", 71);

var document = await collection.Find(filter).FirstAsync();
Console.WriteLine(document);

and it should print just one document:

{ "_id" : ObjectId("5515836e58c7b4fbc756320b"), "i" : 71 }

Get a Set of Documents with a Filter

We can also get a set of documents from our collection. For example, if we wanted to get all documents where i > 50, we could write:

var filter = Builders<BsonDocument>.Filter.Gt("i", 50);

await collection.Find(filter).ForEachAsync(d => Console.WriteLine(d));

We could also get a range, say 50 < i <= 100:

var filterBuilder = Builders<BsonDocument>.Filter;
var filter = filterBuilder.Gt("i", 50) & filterBuilder.Lte("i", 100);

await collection.Find(filter).ForEachAsync(d => Console.WriteLine(d));

Sorting Documents

We add a sort to a find query by calling the Sort method. Below we use the Exists filter builder method and Descending sort builder method to sort our documents:

var filter = Builders<BsonDocument>.Filter.Exists("i");
var sort = Builders<BsonDocument>.Sort.Descending("i");

var document = await collection.Find(filter).Sort(sort).FirstAsync();

Projecting Fields

Many times we don’t need all the data contained in a document. The Projection builder will help build the projection parameter for the find operation. Below we’ll exclude the “_id” field and output the first matching document:

var projection = Builders<BsonDocument>.Projection.Exclude("_id");
var document = await collection.Find(new BsonDocument()).Project(projection).FirstAsync();
Console.WriteLine(document.ToString());

Updating Documents

There are numerous update operators supported by MongoDB.

To update at most 1 document (may be 0 if none match the filter), use the UpdateOneAsync method to specify the filter and the update document. Here we update the first document that meets the filter i == 10 and set the value of i to 110:

var filter = Builders<BsonDocument>.Filter.Eq("i", 10);
var update = Builders<BsonDocument>.Update.Set("i", 110);

await collection.UpdateOneAsync(filter, update);

To update all documents matching the filter use the UpdateManyAsync method. Here we increment the value of i by 100 where i < 100.

var filter = Builders<BsonDocument>.Filter.Lt("i", 100);
var update = Builders<BsonDocument>.Update.Inc("i", 100);

var result = await collection.UpdateOneAsync(filter, update);

if (result.IsModifiedCountAvailable)
{
    Console.WriteLine(result.ModifiedCount);
}

The update methods return an UpdateResult which provides information about the operation including the number of documents modified by the update.

Deleting Documents

To delete at most 1 document (may be 0 if none match the filter) use the DeleteOneAsync method:

var filter = Builders<BsonDocument>.Filter.Eq("i", 110));

await collection.DeleteOneAsync(filter);

To delete all documents matching the filter use the DeleteManyAsync method method. Here we delete all documents where i >= 100:

var filter = Builders<BsonDocument>.Filter.Gte("i", 100));

var result = await collection.DeleteManyAsync(filter);

Console.WriteLine(result.DeletedCount);

The delete methods return a DeleteResult which provides information about the operation including the number of documents deleted.

Bulk Writes

There are two types of bulk operations:

1. Ordered bulk operations.

   Executes all the operations in order and errors out on the first error.

2. Unordered bulk operations.

   Executes all the operations and reports any errors. Unordered bulk operations do not guarantee the order of execution.

Let’s look at two simple examples using ordered and unordered operations:

var models = new WriteModel<BsonDocument>[] 
{
    new InsertOneModel<BsonDocument>(new BsonDocument("_id", 4)),
    new InsertOneModel<BsonDocument>(new BsonDocument("_id", 5)),
    new InsertOneModel<BsonDocument>(new BsonDocument("_id", 6)),
    new UpdateOneModel<BsonDocument>(
        new BsonDocument("_id", 1), 
        new BsonDocument("$set", new BsonDocument("x", 2))),
    new DeleteOneModel<BsonDocument>(new BsonDocument("_id", 3)),
    new ReplaceOneModel<BsonDocument>(
        new BsonDocument("_id", 3), 
        new BsonDocument("_id", 3).Add("x", 4))
};

// 1. Ordered bulk operation - order of operation is guaranteed
await collection.BulkWriteAsync(models);

// 2. Unordered bulk operation - no guarantee of order of operation
await collection.BulkWriteAsync(models, new BulkWriteOptions { IsOrdered = false });