如何使用 LINQ 的 AsQueryable() 从 MongoDB 中的内部数组获取数据？

问题描述

我无法从 MongoDB 的内部数组中获取数据。我收到错误：

BsonSerializationException: No matching creator found.

这是我在 MongoDB、查询和环境中的数据示例。

{
        "Id" : 1,"compName" : "Samsung Electronics Co.","symbol" : "005930-KRX","analyst" : [
                {
                        "analystId" : 4,"analystinit" : "SJ","analystFName" : "Steve","analystLName" : "Jobs","analystemail" : "[e-mail]"
                }
        ],"associates" : [
                {
                        "analystId" : 7,"analystinit" : "BG","analystFName" : "Bill","analystLName" : "Gates","analystemail" : "[e-mail]"
                },{
                        "analystId" : 10,"analystinit" : "MJ","analystFName" : "Michael","analystLName" : "Jordan","analystemail" : "[e-mail]"
                }
        ],"gics" : "75301020","cusip" : null
}

POCO

[BsonIgnoreExtraElements]
class CompanyClass
{
    #region [ Properties ]
    [BsonElement("issuerId")]
    public Int32 IssuerId { get; set; }
    [BsonElement("compName")]
    public string CompName { get; set; }
    [BsonElement("symbol")]
    public string Symbol { get; set; }
    [BsonElement("analyst")]
    public IEnumerable<AnalystClass> Analyst { get; set; }
    [BsonElement("associates")]
    public IEnumerable<AnalystClass> Associates { get; set; }
    [BsonElement("gics")]
    public string Gics { get; set; }
    [BsonElement("cusip")]
    public string Cusip { get; set; }
    #endregion
}
[BsonIgnoreExtraElements]
class AnalystClass
{
    #region [ Properties ]
    [BsonElement("init")]
    public string ResAnInit { get; set; }
    [BsonElement("firstName")]
    public string ResAnFirstName { get; set; }
    [BsonElement("lastName")]
    public string ResAnLastName { get; set; }
    [BsonElement("email")]
    public string ResAnEmail { get; set; }
    #endregion
}

查询：

compCollection = GetMonDB("Companies").GetCollection<CompanyClass>("coverage");
var comps = compCollection.AsQueryable()
.Select(c => new { 
    CompName = c.CompName,Symbol = c.Symbol,ResAnsFName = c.Analyst.Select(x => x.ResAnFirstName)  <-- Problem line
    CUSIP = c.Cusip
});

我想得到这个：

我的环境：

C# MongoDB.Driver = 2.12
MongoDB = 4.2
Windows = Win10

我似乎遗漏了一些明显的东西。我做错了什么？

解决方法

只需像这样进行投影：

var comps = await compCollection
    .AsQueryable()
    .Select(c => new
    {
        ...
        ResAnsFName = c.Analyst.first().ResAnFirstName
        ...
    })
    .ToListAsync();

,

ResAns 属性在 CompanyClass 类中不存在，因此您不能使用该属性。 此外 BsonElements 与您的 MongoDB 数据不匹配。 Select 应该足以执行 Linq，不需要 FirstorDefault 或 ToList()。

 ResAnsFName = c.Analyst.Select(x => x.ResAnFirstName)

更新

BSON：

{ 
  "_id" : ObjectId("59ce6b34f48f171624840b05"),"name" : "Nikola","blog" : "rubikscode.net","age" : 30,"location" : "Beograd" 
}

C# 强类型对象：

    public class User
    {
        [BsonId]
        public ObjectId Id { get; set; }
        [BsonElement("name")]
        public string Name { get; set; }
        [BsonElement("blog")]
        public string Blog { get; set; }
        [BsonElement("age")]
        public int Age { get; set; }
        [BsonElement("location")]
        public string Location { get; set; }
    }