MongoDb 一对多映射

Question

我正在尝试与 MongoDb 建立一对多关系，但坚持加入这两个集合。我在下面做了一个例子，看看我现在是怎么做的。

// schools collection
{
  _id: ObjectId("5ef206d1d21c573718ae6eda")
  name: "Hogwarts School of Witchcraft and Wizardry"
}

// students collection
{
  _id: ObjectId("5efed5df8b28770c2cb344b9"),
  school_id: ObjectId("5ef206d1d21c573718ae6eda")
  firstName: "Harry"
  lastName: "Potter"
}

和.net项目中的模型类：

public class School
{
    [BsonId]
    [BsonRepresentation(BsonType.ObjectId)]
    public string Id { get; set; }
    
    public string Name { get; set; }
    public List<Student> Students { get; set; }
}

public class Student
{
    [BsonId]
    [BsonRepresentation(BsonType.ObjectId)]
    public string Id { get; set; }
    
    [BsonRepresentation(BsonType.ObjectId)]
    [Required]
    public string School_id { get; set; }
    
    public string FirstName { get; set; }
    public string LastName { get; set; }
}

如何将 students 映射到 school 对象？我尝试了这些代码，但其中 none 行得通。

// 1st attempt
var q = _schools.Aggregate().Lookup<School, Student, School>(_students, school => school.Id, student 
=> student.school_id, a => a.Students);

// 2nd attempt
var q = from school in _schools.AsQueryable()
        join student in _students.AsQueryable() on school.Id equals student.school_id into students
        select new School()
        {
            Students = students
        };

var result = q.ToList();

我错过了什么？

Answer 1

实际上这两个代码片段都有效，唯一的错误是我拼错了数据库中的 school_id 值并引用了一个不存在的 School 文档。

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