如何从Bson文档中获取值列表? [英] How to fetch a list of values from a Bson document?

问题描述

我正在解析一个Json文档，该文档使用

I'm parsing in a Json document that stores a list of type <Country> (which holds the name and code), using the MongoDB.Net driver. But I'm not sure how to retrieve that list of countries from the Bson document.

我单步执行了解析代码，所有值都被解析到CountryModel中.然后存储在返回的collection var中.

I stepped through the parsing code, all values are being parsed in to the CountryModel. Then stored in the returned collection var.

Google搜索给我带来了此解决方案，但仅显示了如何通过ID返回记录而不是完整列表.我想知道是否可以在这里使用Lambda重载来查找列表.

Googling brought me this solution but it only shows how to return a record by ID not a complete List. I'm wondering if a Lambda overload can be used here to find the list.

到目前为止，我已经设法检索了完整的文档，并将其分配给列表:

So far I've managed to retrieve the complete doc, and assign it to a list :

countries = collection.Find(new BsonDocument()).ToListAsync().GetAwaiter().GetResult();

有人知道我怎么能只获取List<Country>而不是整个文档?

Does anyone know how I can fetch just List<Country> and not the whole document?

检索数据涉及的两种主要方法如下:

The two main methods involved in retrieving the data are as follows:

    public void LoadDb()
    {
        var collection = StartConnection();          
        countries = collection.Find(new BsonDocument()).ToListAsync().GetAwaiter().GetResult();

    }


    public IMongoCollection<CountryModel> StartConnection()
    {            
        var client = new MongoClient(connectionString);
        var database = client.GetDatabase("orders");
        //Get a handle on the countries collection:
        var collection = database.GetCollection<CountryModel>("countries");
        return collection;
    }

这是在以下位置解析的Json数据的示例:

This is a sample of the Json data that's parsed in:

{
    "_id": {
        "$oid": "565f5d3ae4b0ed465284d17a"
    },
    "countries": [
        {
            "name": "Afghanistan",
            "code": "AF"
        },
        {
            "name": "Antigua and Barbuda",
            "code": "AG"
        }
    ]
}

这是支持POCO的类，CountryModel:

And this is the backing POCO class, CountryModel :

namespace MongoDBApp.Models
{
    [ImplementPropertyChanged]
    public class CountryModel
    {

        [BsonId]
        public ObjectId Id { get; set; }

        [BsonElement("countries")]
        public List<Country> countries { get; set; }



    }

    [ImplementPropertyChanged]
    public class Country
    {
        [BsonElement("name")]
        public string Name { get; set; }

        [BsonElement("code")]
        public string Code { get; set; }
    }
}

推荐答案

尝试投影:

 var result = await collection.Find(x => x.Id == {ObjectId}).Project(x => x.countries).FirstOrDefaultAsync();

{ObjectId} 是要从中获取国家/地区集合的CountryModel的ID.

Where {ObjectId} is the id of the CountryModel from which you want to fetch the countries collection.

顺便说一句:有一种使用ObjectId的更方便的方法.您可以在模型中放置string并添加属性:

Btw: There is more convenient way for using ObjectId. You can place string in your model and add attributes:

[BsonId]
[BsonRepresentation(BsonType.ObjectId)]
public string Id { get; set; }

然后您可以将Find与string中的ID一起使用:

Then you can use Find with Id in string:

 collection.Find(x => x.Id == "sample_object_id")

这篇关于如何从Bson文档中获取值列表?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！