<六>.netcore 查询 MongoDb 其他方法

上一篇试了创建文档,和检索文档的操作，这一篇来试试Find中的一些操作方法。

• Limit，有时不想返回所有文档，就可以用这个方法进行限制数量

var connectionString = "mongodb://localhost:27017";
var client = new MongoClient(connectionString);
var database = client.GetDatabase("School");
var collection = database.GetCollection<StudentNew>("StudentNew");
await collection.Find(x => x.Sex =="男")
    .Limit(2)
    .ForEachAsync(student =>
    {
        Console.WriteLine(student.Name);
    });
class StudentNew
{
    public ObjectId _id { get; set; }
    public string Name { get; set; }
    public string Age { get; set; }
    public IEnumerable<string> Address { get; set; }
    public string Sex { get; set; }
}

• Skip跳过一定数量的文档

var connectionString = "mongodb://localhost:27017";
var client = new MongoClient(connectionString);
var database = client.GetDatabase("School");
var collection = database.GetCollection<StudentNew>("StudentNew");
await collection.Find(x => x.Sex =="男")
    .Skip(1)
    .ForEachAsync(student =>
    {
        Console.WriteLine(student.Name);
    });
class StudentNew
{
    public ObjectId _id { get; set; }
    public string Name { get; set; }
    public string Age { get; set; }
    public IEnumerable<string> Address { get; set; }
    public string Sex { get; set; }
}

• Sort 排序，1：正序排序，-1：倒序排序

var connectionString = "mongodb://localhost:27017";
var client = new MongoClient(connectionString);
var database = client.GetDatabase("School");
var collection = database.GetCollection<StudentNew>("StudentNew");
await collection.Find(x => x.Sex =="男")
    .Sort("{Age:1}")
    .ForEachAsync(student =>
    {
        Console.WriteLine(student.Name);
    });
class StudentNew
{
    public ObjectId _id { get; set; }
    public string Name { get; set; }
    public string Age { get; set; }
    public IEnumerable<string> Address { get; set; }
    public string Sex { get; set; }
}

• Projection投影，即只查询需要查询的字段。

var connectionString = "mongodb://localhost:27017";
var client = new MongoClient(connectionString);
var database = client.GetDatabase("School");
var collection = database.GetCollection<StudentNew>("StudentNew");
await collection.Find(x => x.Sex =="男")
    .Sort("{Age:1}")
    .Project("{Age:1}")
    .ForEachAsync(student =>
    {
        Console.WriteLine(student);
    });
class StudentNew
{
    public ObjectId _id { get; set; }
    public string Name { get; set; }
    public string Age { get; set; }
    public IEnumerable<string> Address { get; set; }
    public string Sex { get; set; }
}