Question

这个问题的原理与this one相同，但是当此对象嵌套在集合的数组中时，我想在对象属性上使用强类型化方法创建索引。

我可以使用：

new CreateIndexModel<T>( Builders<T>.IndexKeys.Ascending( a ) )

其中 a 是可访问直接属性的表达式。

但是我没有发现类似的东西

Builders<Library>.Filter.ElemMatch(x => x.Author.Books, b => b.IsVerified == false));

以便我可以将嵌套在作为集合成员的数组中的对象的某些字段定义为索引。

有可能做到吗？如何做到？

Answer 1

请考虑以下数据模型：

public class Course
{
   public string Name { get; set; }
   public string Teacher { get; set; }
}

public class Student
{
  public string Name { get; set; }
  public int Age { get; set; }
  public ReadOnlyCollection<Course> Courses { get; set; }
}

您可以按以下方式在“课程”字段上创建一个升序的多键索引：

using MongoDB.Driver;
using System;
using System.Collections.Generic;
using System.Threading.Tasks;

namespace ConsoleApp1
{
  public static class Program
  {
    private static MongoClient Client;
    private static IMongoDatabase Database;
    private static IMongoCollection<Student> Collection;

    public static async Task Main(string[] args)
    {
      Client = new MongoClient();
      Database = Client.GetDatabase("test-index");
      Collection = Database.GetCollection<Student>("students");

      var courses1 = new List<Course>()
      {
        new Course { Name = "Math", Teacher = "Bob" }
      }.AsReadOnly();

      var courses2 = new List<Course>()
      {
        new Course { Name = "Computer Science", Teacher = "Alice" }
      }.AsReadOnly();

      var mark = new Student
      {
        Name = "Mark",
        Courses = courses1,
        Age = 20
      };

      var lucas = new Student
      {
        Name = "Lucas",
        Courses = courses2,
        Age = 22
      };

      await Collection.InsertManyAsync(new[] { mark, lucas }).ConfigureAwait(false);


      var model = new CreateIndexModel<Student>(
        Builders<Student>.IndexKeys.Ascending(s => s.Courses));

      await Collection.Indexes.CreateOneAsync(model).ConfigureAwait(false);

      Console.WriteLine("All done !");
    }
  }
}

此查询由您创建的索引提供： db.students.find({Courses: {"Name": "Math", "Teacher": "Bob"}})

如果您不想在整个数组Courses上创建索引，而是想要在嵌套对象（Course对象）的Name字段上创建索引，这是一种方法：

using MongoDB.Driver;
using System;
using System.Collections.Generic;
using System.Threading.Tasks;

namespace ConsoleApp1
{
  public static class Program
  {
    private static MongoClient Client;
    private static IMongoDatabase Database;
    private static IMongoCollection<Student> Collection;

    public static async Task Main(string[] args)
    {
      Client = new MongoClient();
      Database = Client.GetDatabase("test-index");
      Collection = Database.GetCollection<Student>("students");

      var courses1 = new List<Course>()
      {
        new Course { Name = "Math", Teacher = "Bob" }
      }.AsReadOnly();

      var courses2 = new List<Course>()
      {
        new Course { Name = "Computer Science", Teacher = "Alice" }
      }.AsReadOnly();

      var mark = new Student
      {
        Name = "Mark",
        Courses = courses1,
        Age = 20
      };

      var lucas = new Student
      {
        Name = "Lucas",
        Courses = courses2,
        Age = 22
      };

      await Collection.InsertManyAsync(new[] { mark, lucas }).ConfigureAwait(false);


      var model = new CreateIndexModel<Student>(
        Builders<Student>.IndexKeys.Ascending("Courses.Name"));

      await Collection.Indexes.CreateOneAsync(model).ConfigureAwait(false);

      Console.WriteLine("All done !");
    }
  }
}

此查询由您创建的索引提供：db.students.explain("executionStats").find({"Courses.Name": "Math"})

在我的第二个示例中，避免使用魔术字符串的一种可能方法是利用C＃运算符nameof的功能： $"{nameof(Student.Courses)}.{nameof(Course.Name)}"

Answer 2

这是使用MongoDB.Entities便捷库为嵌套字段创建索引的强类型方法。 [免责声明：我是作者]

using MongoDB.Entities;
using System.Collections.Generic;

namespace StackOverflow
{
    public class Program
    {
        public class Parent : Entity
        {
            public Child[] Children { get; set; }
        }

        public class Child
        {
            public List<Friend> Friends { get; set; }
        }

        public class Friend
        {
            public string Name { get; set; }
        }

        static void Main(string[] args)
        {
            new DB("test");

            DB.Index<Parent>()
              .Key(p => p.Children[-1].Friends[-1].Name, KeyType.Ascending)
              .Create();

        }
    }
}

上面的代码在name字段上创建一个升序索引，该字段使用以下命令嵌套在两层深处：

db.Parent.createIndex({
    "Children.Friends.Name": NumberInt("1")
}, {
    name: "Children.Friends.Name(Asc)",
    background: true
})

如何在C＃Mongodb强类型驱动程序中基于嵌套数组元素创建索引

2 个答案: