Creating MongoDB Unique Key with C#

Question

I am fighting to create a unique field EmailAddress. I've already seen in forums that I have to create an index, but it didn't work out for me so far. Does anyone have a code example? Do I have to create the index on every save/call, or is it enough to create it only once?

I tried this code:

DB.GetCollection<User>(Dbname)     .EnsureIndex(new IndexKeysBuilder()         .Ascending("EmailAddress"), IndexOptions.SetUnique(true));  DB.GetCollection<User>(Dbname).Save(user, SafeMode.True); 

My User model looks like this:

public class User {     [Required(ErrorMessage = "Email Required")]     public string EmailAddress { get; set; }      public ObjectId Id { get; set; }      public string FirstName { get; set; }     public string LastName { get; set; } } 

Answer 1

The unique index only needs to be created once, after that any document inserts that contain a duplicate email address will fail. Here's an example:

var server = MongoServer.Create("mongodb://localhost"); var db = server.GetDatabase("myapp");  var users = db.GetCollection<User>("users");  users.EnsureIndex(new IndexKeysBuilder()     .Ascending("EmailAddress"), IndexOptions.SetUnique(true));  var user1 = new User { EmailAddress = "[email protected]" }; var user2 = new User { EmailAddress = "[email protected]" };  try {     users.Save(user1, WriteConcern.Acknowledged);     users.Save(user2, WriteConcern.Acknowledged);  // <-- throws MongoSafeModeException } catch (MongoSafeModeException ex) {     Console.WriteLine(ex.Message); } 

Answer 2

EnsureIndex() is deprecated/obsolete per the C# mongo drivers version 2.0 spec: http://api.mongodb.org/csharp/current/html/M_MongoDB_Driver_MongoCollection_EnsureIndex_2.htm

heres how to do it async and via 2.0 code:

var mongoClient = new MongoClient("connection"); var db = mongoClient.GetDatabase("database");  var options = new CreateIndexOptions() { Unique = true }; var field = new StringFieldDefinition<User>("EmailAddress"); var indexDefinition = new IndexKeysDefinitionBuilder<User>().Ascending(field); await db.GetCollection<Users>("users").Indexes.CreateOneAsync(indexDefinition, options); 

In case of a non-string index:

   var options = new CreateIndexOptions() { Unique = true };    IndexKeysDefinition<Foo> keyCode = "{ Code: 1 }";    var codeIndexModel = new CreateIndexModel<Foo>(keyCode, options);