对于名为"id"的字段，MongoDB LINQ提供程序的奇怪行为是: [英] Strange behavior of MongoDB LINQ provider for fields called "id"

问题描述

这是Mongo LINQ提供程序失败的JSON文档:

Here's a JSON document where Mongo LINQ provider fails:

{"results":
     {"text":"@twitterapi  http://tinyurl.com/ctrefg",
     "to_user_id":396524,
     "to_user":"TwitterAPI",
     "from_user":"jkoum",
     "metadata":
     {
      "result_type":"popular",
      "recent_retweets": 109
     },
     "id":1478555574, 
     "from_user_id":1833773,
     "iso_language_code":"nl",
     "source":"<a href=\"http://twitter.com/\">twitter<\/a>",
     "profile_image_url":"http://s3.amazonaws.com/twitter_production/profile_images/118412707/2522215727_a5f07da155_b_normal.jpg",
     "created_at":"Wed, 08 Apr 2009 19:22:10 +0000",
     "since_id":0,
     "max_id":1480307926,
     "refresh_url":"?since_id=1480307926&q=%40twitterapi",
     "results_per_page":15,
     "next_page":"?page=2&max_id=1480307926&q=%40twitterapi",
     "completed_in":0.031704,
     "page":1,
     "query":"%40twitterapi"}
}

请注意一个"id"字段.以下是相关的C#实体定义:

Note an "id" field. Here are related C# entity definitions:

class Twitter
{
    [BsonId]
    public ObjectId Id { get; set; }
    public Result results { get; set; }
}

private class Result
{
    public string text { get; set; }
    public int to_user_id { get; set; }
    public string to_user { get; set; }
    public string from_user { get; set; }
    public Metadata metadata { get; set; }
    public int id { get; set; }
    public int from_user_id { get; set; }
    public string iso_language_code { get; set; }
    public string source { get; set; }
    public string profile_image_url { get; set; }
    public string created_at { get; set; }
    public int since_id { get; set; }
    public int max_id { get; set; }
    public string refresh_url { get; set; }
    public int results_per_page { get; set; }
    public string next_page { get; set; }
    public double completed_in { get; set; }
    public int page { get; set; }
    public string query { get; set; }
}

class Metadata
{
    public string result_type { get; set; }
    public int recent_retweets { get; set; }
}

如果创建"Twitter"集合并保存上面的文档，则当我使用Mongo LINQ提供程序对其进行查询时，它将引发FileFormatException异常: 元素'id'与Mongo.Context.Tests.NativeTests + Result类的任何字段或属性都不匹配"

If I create a "Twitter" collection and save the document above, then when I query it using Mongo LINQ provider, it throws a FileFormatException exception: "Element 'id' does not match any field or property of class Mongo.Context.Tests.NativeTests+Result"

但是，有两种替代方法可以解决此问题:

However there are two alternative workarounds to fix this problem:

1. 重命名结果"id"字段，例如JSON文档和Result类中的"idd".然后LINQ查询开始工作.
2. 保留"id"字段，但还要在Result类中添加字段"Id"，并使用属性[BsonId]对其进行标记.现在Result类同时包含"Id"和"id"字段，但查询有效！

我使用Mongo API查询集合，一切正常，所以我想这一定是MongoDB LINQ提供程序中的错误.嵌套JSON元素中的"id"不应该是保留的作品，对吗?

I use Mongo API to query the collection, everything works fine, so I guess this must be a bug in a MongoDB LINQ provider. "id" in a nested JSON element should not be a reserved work, should it?

更新:这是本机API查询执行的结果:

UPDATE: Here's the result of a native API query execution:

> db.Twitter.find().limit(1);

{ "_id" : ObjectId("50c9d3a4870f4f17e049332b"),
 "results" : { 
    "text" : "@twitterapi  http://tinyurl.com/ctrefg", 
    "to_user_id" : 396524, 
    "to_user" : "TwitterAPI", 
    "from_user" : "jkoum", 
    "metadata" : { "result_type" : "popular", "recent_retweets" : 109 }, 
    "id" : 1478555574, 
    "from_user_id" : 1833773, "
    iso_language_code" : "nl", 
    "source" : "<a href=\"http://twitter.com/\">twitter</a>", 
    "profile_image_url" : "http://s3.amazonaws.com/twitter_production/profile_images/118412707/2522215727_a5f07da155_b_normal.jpg", 
    "created_at" : "Wed, 08 Apr 2009 19:22:10 +0000", 
    "since_id" : 0, 
    "max_id" : 1480307926, 
    "refresh_url" : "?since_id=1480307926&q=%40twitterapi", "results_per_page" : 15,    "next_page" : "?page=2&max_id=1480307926&q=%40twitterapi", 
    "completed_in" : 0.031704, 
    "page" : 1, 
    "query" : "%40twitterapi" 
    } 
}

推荐答案

MongoDB要求存储在数据库中的每个文档都有一个名为"_id"的字段(在根级别).

MongoDB requires that every document stored in the database have a field (at the root level) called "_id".

C#驱动程序假定您的类中称为"Id"，"id"或"_id"的任何字段都应映射到特殊的"_id"字段.这是一个约定，可以重写. C#驱动程序不知道您的Result类不是要用作集合的根文档，因此它会找到您的"id"字段并将其映射到数据库中的"_id".

The C# driver assumes that any field in your class called "Id", "id" or "_id" is meant to be mapped to the special "_id" field. This is a convention, one that can be overridden. The C# driver doesn't know that your Result class isn't meant to be used as the root document of a collection, so it finds your "id" field and maps it to "_id" in the database.

您可以重写此方法的一种方法是更改​​类中字段的名称(如您所发现的).然后，您还可以使用[BsonElement]属性将C#字段名称(例如"idd")映射到数据库中实际使用的任何名称(例如"id").例如:

One way you can override this is to change the name of the field in your class (as you discovered). What you can then also do is use the [BsonElement] attribute to map your C# field name (e.g. "idd") to whatever name is actually being used in the database (e.g. "id"). For example:

public class Result
{
    [BsonElement("id")]
    public int idd; // matches "id" in the database
    // other fields
}

另一种替代方法是覆盖查找类的"Id"成员的约定，以禁止Result类的C#驱动程序的默认行为.您可以通过为Result类注册一个新的ConventionProfile来实现.例如:

Another alternative is to override the convention that finds the "Id" member of a class to suppress the default behavior of the C# driver for your Result class. You can do this by registering a new ConventionProfile for your Result class. For example:

var noIdConventions= new ConventionProfile();
noIdConventions.SetIdMemberConvention(new NamedIdMemberConvention()); // no names
BsonClassMap.RegisterConventions(noIdConventions, t => t == typeof(Result));

在确定Result类映射之前，您必须确保在程序的早期执行此操作.

You must be sure to do this very early in your program, before your Result class gets mapped.

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