Introduction to the 10gen C# Driver

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MongoDB C# Driver

New 10gen supported driverRobert Stam

Lead Engineer C# Driver

Highlights

• Full featured• High performance• Rapidly tracks new releases of MongoDB• Fully supported by 10gen

Release Timeline

• v0.5 released October 15, 2010• v0.7 released November 3, 2010• v0.9 releasing soon• v1.0 releasing within 1-2 months

Downloading

Binaries:http://github.com/mongodb/mongo-csharp-driver/downloads

In .zip and .msi formatsSource code:http://github.com/mongodb/mongo-csharp-driver

Documentation:http://www.mongodb.org/display/DOCS/Drivers

Adding References

• Add References to:– MongoDB.Bson.dll– MongoDB.Driver.dll

• From where?– C:\Program Files (x86)\MongoDB\...– …\mongo-csharp-driver\Driver\bin\Debug

Namespacesusing MongoDB.Bson;using MongoDB.Driver;

// sometimesusing MongoDB.Bson.IO;using MongoDB.Bson.Serialization;using MongoDB.Bson.DefaultSerializer;using MongoDB.Driver.Builders;

BSON Document

• A MongoDB database holds collections of BSON documents

• A BSON document is a collection of elements• A BSON element has:– a name– a type– a value

BSON Object Model

• A set of classes that represent a BSON document in memory

• Important classes:– BsonDocument– BsonElement– BsonValue (and its subclasses)– BsonType (an enum)

BsonValue subclasses

• One subclass for each BsonType• Examples:– BsonInt32/BsonInt64– BsonString– BsonDateTime– BsonArray– BsonDocument (embedded document)– and more…

Sample BsonDocument// using functional constructionvar book = new BsonDocument( new BsonElement(“Author”, “Ernest Hemingway”), new BsonElement(“Title”,

“For Whom the Bell Tolls”));

Sample BsonDocument (continued)// using collection initializer syntaxvar book = new BsonDocument { { “Author”, “Ernest Hemingway” }, { “Title”, “For Whom the Bell Tolls” }};

// compiler converts that tovar book = new BsonDocument();book.Add(“Author”, “Ernest Hemingway”);book.Add(“Title”, “For Whom the Bell Tolls”);

Sample BsonDocument (continued)// using fluent interfacevar book = new BsonDocument() .Add(“Author”, “Ernest Hemingway”) .Add(“Title”, “For Whom the Bell Tolls”);

Accessing BSON Document Elements

BsonValue value = document[“name”];

string author = book[“Author”].AsString;string author = (string) book[“Author”];string author = (string) book[“Author”, null];

int year = book[“PublicationYear”].AsInt32;bool outOfPrint = book[“OutOfPrint”].AsBoolean;bool outOfPrint = book[“OutOfPrint”].ToBoolean();

BsonElement element = document.GetElement(“name”);

C# Driver Classes

• Main classes:– MongoServer– MongoDatabase– MongoCollection– MongoCursor

These top level classes are all thread safe.(MongoCursor is thread safe once frozen).

MongoServervar server = MongoServer.Create();// orvar url = “mongodb://localhost:27017”;var server = MongoServer.Create(url);

One instance is created for each URL. Subsequent calls to Create with the same URL return the same instance.

Not [Serializable], so don’t put in session state.

Connection Strings (URLs)

Connection string format:mongodb://[credentials@]hosts[/[database][?options]]

Examples:mongodb://server1mongodb://server1:27018mongodb://username:password@server1/employeesmongodb://server1,server2,server3mongodb://server1,server2,server3/?slaveok=truemongodb://localhost/?safe=true

/?optionsconnect=direct|replicasetreplicaset=name (implies connect=replicaset)slaveok=true|falsesafe=true|falsew=n (implies safe=true)wtimeout=ms (implies safe=true)fsync=true|false (implies safe=true)

Documentation at:http://www.mongodb.org/display/DOCS/Connections

Connection Modes

• Direct– If multiple host names are provided they are tried

in sequence until a match is found• Replica set– Multiple host names are treated as a seed list. All

hosts are contacted in parallel to find the current primary. The seed list doesn’t have to include all the members of the replica set. If the replica set name was provided it will be verified.

slaveok

• If connect=direct– If slaveok=true then it is OK if the server is not a

primary (useful to connect directly to secondaries in a replica set)

• If connect=replicaset– If slaveok=true then all writes are sent to the

primary and reads are distributed round-robin to the secondaries

Connection Pools

• The driver maintains one connection pool for each server it is connected to

• The connections are shared among all threads• A connection is normally returned to the

connection pool as soon as possible (there is a way for a thread to temporarily hold on to a connection)

MongoDatabaseMongoDatabase test = server["test"];

// orMongoCredentials credentials =

new MongoCredentials(username, password);MongoDatabase test = server["test", credentials];

// orMongoDatabase test = server[“test”, SafeMode.True];

One instance is created for each combination of name, credentials and safemode. Subsequent calls with the same values return the same instance.

MongoCollectionMongoCollection<BsonDocument> books = test["books"];MongoCollection<BsonDocument> books = test.GetCollection("books");

// or

MongoCollection<Book> books = test.GetCollection<Book>("books");

Book is default document type

MongoCollection (continued)var books = database[“books”, SafeMode.True];var books = database.GetCollection<Book>( “books”, SafeMode.True);

One instance is created for each combination of name, TDefaultDocument and safemode. Subsequent calls with the same values return the same instance.

Insertvar books = database[“books”];var book = new BsonDocument { { “Author”, “Ernest Hemingway” }, { “Title”, “For Whom the Bell Tolls” }};SafeModeResult result = books.Insert(book);

Returns a SafeModeResult (null if not using safemode). Consider using InsertBatch if inserting multiple documents.

Insert (using serialization)// Book is a class with Author and Title propertiesvar books = database.GetCollection<Book>(“books”);var book = new Book { Author = “Ernest Hemingway”, Title = “For Whom the Bell Tolls”};var result = books.Insert(book);

The book instance will be serialized to a BSON document (see Serialization and DefaultSerializer).

FindOnevar books = database[“books”];var book = books.FindOne(); // returns BsonDocument

FindOne (using serialization)var books = database[“books”];var book = books.FindOneAs<Book>(); // returns Book instead of BsonDocument

or

var books = database.GetCollection<Book>(“books”);var book = books.FindOne(); // returns Book // because Book is default document type

Find (with query)var query = new BsonDocument { { “Author”, “Ernest Hemingway” }};var cursor = books.Find(query);foreach (var book in cursor) { // process book}

Find (with Query builder)var query = Query.EQ(“Author”, “Ernest Hemingway”);var cursor = books.Find(query);foreach (var book in cursor) { // process book}

// a more complicated queryvar query = Query.And( Query.EQ(“Author”, “Ernest Hemingway”), Query.GTE(“PublicationYear”, 1950));

Cursor options

• A cursor can be modified before being enumerated (before it is frozen)

var query = Query.GTE(“PublicationYear”, 1950);var cursor = books.Find(query);cursor.Skip = 100;cursor.Limit = 10;foreach (var book in cursor) { // process 10 books (first 100 skipped)}

Cursor options (fluent interface)var query = Query.GTE(“PublicationYear”, 1950);var cursor = books.Find(query);foreach (var book in cursor.SetSkip(100).SetLimit(10)) { // process 10 books (first 100 skipped)}

// or even shortervar query = Query.GTE(“PublicationYear”, 1950);foreach (var book in books.Find(query).SetSkip(100).SetLimit(10)) { // process 10 books (first 100 skipped)}

Updatevar query = Query.EQ(“Title”, “For Who”);var update = new BsonDocument { { “$set”, new BsonDocument { { “Title”, “For Whom the Bell Tolls” } }}};SafeModeResult result = books.Update(query, update);

Update (using Update builder)var query = Query.EQ(“Title”, “For Who”);var update = Update.Set(“Title”, “For Whom the Bell Tolls”);SafeModeResult result = books.Update(query, update);

Save

• If it’s a new document calls Insert otherwise calls Update

var query = Query.EQ(“Title”, “For Who”);var book = books.FindOne(query);book.Title = “For Whom the Bell Tolls”;SafeModeResult result = book.Save();

How does Save know whether it’s a new document or not? (It looks at the _id value).

Removevar query = Query.EQ(“Author”, “Ernest Hemingway”);SafeModeResult result = books.Remove(query);

// also

books.RemoveAll();books.Drop();

RequestStart/RequestDone

• When a sequence of operations all need to occur on the same connection wrap the operations with calls to RequestStart/RequestDone

• RequestStart is per thread• For the duration of the Request the thread holds

and uses a single connection, which is not returned to the pool until RequestDone is called

• Calls to RequestStart can be nested. The request ends when the nesting level reaches zero again.

RequestStart (continued)

• RequestStart and the using statement– Return value of RequestStart is a helper object

that implements IDisposable– RequestDone is called for you automatically when

the using statement terminates

using (server.RequestStart(database)) { // a series of related operations }

RunCommand

• Wrapper methods are provided for many commands, but you can always run them yourself

var command = new BsonDocument(“collstats”, “books”);CommandResult result = database.RunCommand(command);

CommandResult result = server.RunAdminCommand(“buildinfo”);

Sample Command Wrappers

• CreateCollection• DropCollection• Eval• GetStats• Validate

More MongoCollection Methods

• Count• CreateIndex/EnsureIndex/DropIndex• Distinct• FindAndModify/FindAndRemove• GeoNear• Group• MapReduce

SafeMode

• Write operations can be followed by a call to GetLastError to verify that they succeeded

• SafeMode examples:

SafeMode.FalseSafeMode.TrueSafeMode.W2new SafeMode(3, TimeSpan.FromSeconds(1))

SafeMode at different levels

• SafeMode options can be set at– MongoServer– MongoDatabase– MongoCollection– Individual operation

• SafeMode options are set at the time the instance is created (required for thread safety)

Serialization

• C# classes are mapped to BSON documents• AutoMap:– Public fields and properties

• Lots of ways to customize serialization– IBsonSerializable– IBsonSerializer (call BsonSerializer.RegisterSerializer)– Replace one or more default conventions– [Bson…] Attributes (like DataContract)– BsonClassMap.RegisterClassMap

GridFS

• MongoDB’s Grid file system

var gridFS = database.GridFS;var fileInfo = gridFS.Upload(“filename”);gridFS.Download(“filename”);

// or

var fileInfo = gridFS.Upload(stream, “remotename”);gridFS.Download(stream, “remotename”);

GridFS Streams

• Allow you to treat files stored in GridFS as if they were local files

var gridFS = database.GridFS;var stream = gridFS.Create(“remotename”);// stream implements .NET’s Stream API

// more examplesvar stream = gridFS.OpenRead(“remotename”);var stream = gridFS.Open(“remotename”, FileMode.Append);

Presentation Available Online

• Slides available at:

http://www.slideshare.net/mongodb

• Webinar available at:

http://www.10gen.com/webinars/csharp