获取只有一个指定字段

Question

我已经阅读这个例子：

SELECT A，B FROM用户WHERE年龄= 33 db.users.find（{年龄：33}，{一个：1，B： 1}）

但我不能将它翻译成C＃。谁能帮我？

Answer 1

则可以使用方法类的MongoCursorSetFields，下面完整的例子做：

var server = MongoServer.Create(connectionString); 
var db = _server.GetDatabase("dbName"); 
db.GetCollection("users"); 

var cursor = Photos.FindAs<DocType>(Query.EQ("age", 33)); 
cursor.SetFields(Fields.Include("a", "b")); 
var items = cursor.ToList(); 

Answer 2

我已经翻译下面用C＃新的驱动程序（2.2）

var mongoClient = new MongoClient(""mongodb://127.0.0.1:27017""); 
var database = mongoClient.GetDatabase("databaseName"); 
IMongoCollection<Users> _collection = database.GetCollection<Users>("Users"); 
var condition = Builders<Users>.Filter.Eq(p => p.age, 33); 
var fields = Builders<Users>.Projection.Include(p => p.a).Include(p => p.b); 
var results= _collection.Find(condition).Project<Users>(fields).ToList().AsQueryable(); 

Answer 3

//create user class 
//(not sure how your class looks like) 

public class User 
{ 
[DataMember(Name = "age")] 
public int age; 
[DataMember(Name = "a")] 
public string int a; 
[DataMember(Name = "b")] 
public string int b; 
} 

//then you can use LINQ easily 

var server = MongoServer.Create(connectionString); 
var db = _server.GetDatabase("dbName"); 
var usersCollection = server.GetCollection<User>("users"); 

var filteredCollection = usersCollection.AsQueryable().Where(x=> x.age < 33).Where(x=> x.a != null).Contains(x=> x.b != null); 

Answer 4

查询你可以使用匿名类

public class User 
    { 
     public int age; 
     public string a; 
     public string b; 
    } 

    var collection = db.GetCollection<User>("Users"); 
    var results = collection.Find(Builders<User>.Filter.Eq(user => user.age, 33)) 
      .Project(u => new { u.a, u.b }).ToList();