使用C#创建MongoDB唯一键

Question

我与MongoDB共计n00b,我正在努力创造一个独特的领域EmailAddress.我已经在论坛中看到我必须创建一个索引,但到目前为止它对我来说并没有用.有人有代码示例吗？我是否必须在每次保存/调用时创建索引,还是只创建一次？

我试过这段代码:

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

DB.GetCollection<User>(Dbname).Save(user, SafeMode.True);

我的User模型看起来像这样:

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

只需创建一次唯一索引,之后包含重复电子邮件地址的任何文档插入都将失败.这是一个例子:

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 = "joe@example.com" };
var user2 = new User { EmailAddress = "joe@example.com" };

try
{
    users.Save(user1, WriteConcern.Acknowledged);
    users.Save(user2, WriteConcern.Acknowledged);  // <-- throws MongoSafeModeException
}
catch (MongoSafeModeException ex)
{
    Console.WriteLine(ex.Message);
}

Answer 2

根据C#mongo驱动程序2.0版规范,不推荐使用EnsureIndex():http://api.mongodb.org/csharp/current/html/M_MongoDB_Driver_MongoCollection_EnsureIndex_2.htm

继承人如何做异步和通过2.0代码:

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);

Answer 3

你的代码看起来正确.这是一个完整运行的程序供您比较:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using MongoDB.Bson;
using MongoDB.Driver;
using MongoDB.Driver.Builders;

namespace TestEnsureIndexOnEmailAddress {
    public class User {
        public ObjectId Id;
        public string FirstName;
        public string LastName;
        public string EmailAddress;
    }

    public static class Program {
        public static void Main(string[] args) {
            var server = MongoServer.Create("mongodb://localhost/?safe=true");
            var database = server["test"];
            var users = database.GetCollection<User>("users");
            if (users.Exists()) { users.Drop(); }

            users.EnsureIndex(IndexKeys.Ascending("EmailAddress"), IndexOptions.SetUnique(true));
            var john = new User { FirstName = "John", LastName = "Smith", EmailAddress = "jsmith@xyz.com" };
            users.Insert(john);
            var joe = new User { FirstName = "Joe", LastName = "Smith", EmailAddress = "jsmith@xyz.com" };
            users.Insert(joe); // should throw exception
        }
    }
}

您还可以使用mongo shell确认索引已创建:

> db.users.getIndexes()
[
        {
                "name" : "_id_",
                "ns" : "test.users",
                "key" : {
                        "_id" : 1
                },
                "v" : 0
        },
        {
                "_id" : ObjectId("4de8152ee447ad2550e3b5fd"),
                "name" : "EmailAddress_1",
                "ns" : "test.users",
                "key" : {
                        "EmailAddress" : 1
                },
                "unique" : true,
                "v" : 0
        }
]
>

Answer 4

从下面的 2.8 开始，是创建索引的方法。请注意最后两行。CreateOneAsync(indexDefinition, options)已过时。

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);

var indexModel = new CreateIndexModel<User>(indexDefinition,options);
await db.GetCollection<Users>("users").Indexes.CreateOneAsync(indexModel);