对于使用MongoDB C#Driver 2.0的某些属性，C#中的聚合确实返回null

我正在编写一个MongoDB应用程序，并在C#fow复杂查询中使用聚合管道。 当我将C#生成的聚合复制到shell中时，一切似乎都很好。但是，在C#中执行聚合时，某些属性被设置为

null

。有关更多信息，请参见下文

首先，让我向您展示我的模型：

public class Smartphone
{
    #region Properties

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

    [BsonElement("name")]
    [BsonIgnoreIfNull]
    [BsonIgnoreIfDefault]
    public string Name { get; set; }

    [BsonElement("description")]
    [BsonIgnoreIfNull]
    [BsonIgnoreIfDefault]
    public string Description { get; set; }

    [BsonElement("typenr")]
    [BsonIgnoreIfNull]
    [BsonIgnoreIfDefault]
    public string Type { get; set; }

    [BsonElement("props")]
    [BsonIgnoreIfNull]
    [BsonIgnoreIfDefault]
    public List<SmartphoneProperty> Properties { get; set; }

    #endregion
}

public class UnwindedSmartphone
{
    #region Properties

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

    [BsonElement("name")]
    [BsonIgnoreIfNull]
    [BsonIgnoreIfDefault]
    public string Name { get; set; }

    [BsonElement("description")]
    [BsonIgnoreIfNull]
    [BsonIgnoreIfDefault]
    public string Description { get; set; }

    [BsonElement("typenr")]
    [BsonIgnoreIfNull]
    [BsonIgnoreIfDefault]
    public string Type { get; set; }

    [BsonElement("props")]
    [BsonIgnoreIfNull]
    [BsonIgnoreIfDefault]
    public SmartphoneProperty Property { get; set; }

    #endregion
}

public class SmartphoneProperty
{
    #region Properties

    [BsonElement("type")]
    [BsonIgnoreIfNull]
    [BsonIgnoreIfDefault]
    public string Type { get; set; }

    [BsonElement("value")]
    [BsonIgnoreIfNull]
    [BsonIgnoreIfDefault]
    public string Value { get; set; }

    #endregion
}

需要执行的聚合命令如下所示：

{
    "_id" : ObjectId("55d45c0285afc59c146f66f0"),
    "name" : "LG Nexus 6",
    "description" : "A Nexus 6 device, created by Google.",
    "typenr" : "LG-NEX-5/BLACK",
    "props" : [ 
        {
            "type" : "os",
            "value" : "Android"
        }, 
        {
            "type" : "storage",
            "value" : "8"
        }, 
        {
            "type" : "storage",
            "value" : "16"
        }, 
        {
            "type" : "storage",
            "value" : "32"
        }, 
        {
            "type" : "storage",
            "value" : "64"
        }
    ]
}

// Get all the amount of filters that are defined.
db.smartphones.aggregate([
    // Unwind the "props".
    { "$unwind" : "$props" },

    // Grouping phase.
    // Group by unique properties, add a count for the amount of articles, and add articles to an element named "articles".
    // We use the function "$addToSet" here to ensure that only unique articles are being added.
    { 
        "$group" : { 
            "_id" : "$props", 
            count : { "$sum" : 1 }, 
            articles: { 
                "$addToSet": { 
                    name: "$name", 
                    description: "$description", 
                    typenr: "$typenr" 
                } 
            } 
        } 
    },

    // Sort the results based on the "_id" field.
    { "$sort" : { "_id" : 1 } }
]);

"_id" : {
    "type" : "storage",
    "value" : "128"
},
"count" : 1.0000000000000000,
"articles" : [ 
    {
        "name" : "Apple iPhone 6",
        "description" : "An iPhone 6 device, created by Apple.",
        "typenr" : "APP-IPHONE-6/BLACK"
    }
]

// Get all the amount of filters that are defined.
db.smartphones.aggregate([
    // Unwind the "props".
    { "$unwind" : "$props" }, 

    // Grouping phase.
    // Group by unique properties, add a count for the amount of articles, and add articles to an element named "articles".
    // We use the function "$addToSet" here to ensure that only unique articles are being added.
    { 
        "$group" : { 
            "_id" : "$props", 
            "count" : { "$sum" : 1 }, 
            "articles" : { 
                "$addToSet" : { 
                    "name" : "$name", 
                    "description" : "$description", 
                    "typenr" : "$typenr" 
                } 
            } 
        } 
    }, 
    { "$sort" : { "_id" : 1 } }
])

var aggregation = collection.Aggregate()
    .Unwind<Smartphone, UnwindedSmartphone>(x => x.Properties)
    .Group(key => key.Property, g => new
    {
        Count = g.Count(),
        Articles = g.Select(x => new AggregatedSmartphoneArticle
        {
            Name = x.Name,
            Description = x.Description,
            Type = x.Type
        }).Distinct()
    });

此聚合的单个结果将返回以下结果：

{
    "_id" : ObjectId("55d45c0285afc59c146f66f0"),
    "name" : "LG Nexus 6",
    "description" : "A Nexus 6 device, created by Google.",
    "typenr" : "LG-NEX-5/BLACK",
    "props" : [ 
        {
            "type" : "os",
            "value" : "Android"
        }, 
        {
            "type" : "storage",
            "value" : "8"
        }, 
        {
            "type" : "storage",
            "value" : "16"
        }, 
        {
            "type" : "storage",
            "value" : "32"
        }, 
        {
            "type" : "storage",
            "value" : "64"
        }
    ]
}

// Get all the amount of filters that are defined.
db.smartphones.aggregate([
    // Unwind the "props".
    { "$unwind" : "$props" },

    // Grouping phase.
    // Group by unique properties, add a count for the amount of articles, and add articles to an element named "articles".
    // We use the function "$addToSet" here to ensure that only unique articles are being added.
    { 
        "$group" : { 
            "_id" : "$props", 
            count : { "$sum" : 1 }, 
            articles: { 
                "$addToSet": { 
                    name: "$name", 
                    description: "$description", 
                    typenr: "$typenr" 
                } 
            } 
        } 
    },

    // Sort the results based on the "_id" field.
    { "$sort" : { "_id" : 1 } }
]);

"_id" : {
    "type" : "storage",
    "value" : "128"
},
"count" : 1.0000000000000000,
"articles" : [ 
    {
        "name" : "Apple iPhone 6",
        "description" : "An iPhone 6 device, created by Apple.",
        "typenr" : "APP-IPHONE-6/BLACK"
    }
]

// Get all the amount of filters that are defined.
db.smartphones.aggregate([
    // Unwind the "props".
    { "$unwind" : "$props" }, 

    // Grouping phase.
    // Group by unique properties, add a count for the amount of articles, and add articles to an element named "articles".
    // We use the function "$addToSet" here to ensure that only unique articles are being added.
    { 
        "$group" : { 
            "_id" : "$props", 
            "count" : { "$sum" : 1 }, 
            "articles" : { 
                "$addToSet" : { 
                    "name" : "$name", 
                    "description" : "$description", 
                    "typenr" : "$typenr" 
                } 
            } 
        } 
    }, 
    { "$sort" : { "_id" : 1 } }
])

var aggregation = collection.Aggregate()
    .Unwind<Smartphone, UnwindedSmartphone>(x => x.Properties)
    .Group(key => key.Property, g => new
    {
        Count = g.Count(),
        Articles = g.Select(x => new AggregatedSmartphoneArticle
        {
            Name = x.Name,
            Description = x.Description,
            Type = x.Type
        }).Distinct()
    });

现在，在C#中，我用以下方式编写了聚合：

var aggregation = collection.Aggregate()
    .Unwind<Smartphone, UnwindedSmartphone>(x => x.Properties)
    .Group(key => key.Property, g => new
    {
        Id = g.Key,
        count = g.Count(),
        articles = g.Select(x => new
        {
            name = x.Name,
            description = x.Description,
            typenr = x.Type
        }).Distinct()
    })
    .SortBy(x => x.Id);

因此，它与我试图转换为C代码的原始聚合相同，只是属性用双引号括起来，但这不是问题

如果我在shell中执行此聚合，结果很好。 但是，在C#中执行时，

articles

属性的

name

、

description

和

typenr

具有

null

值

有谁知道为什么会这样吗？

好的

感谢@BlakesSeven为我指明了正确的方向（见他对我问题的评论，我现在知道我为什么会有这个问题）

我需要转换

组中的
select
语句

可能不会返回匿名类型。 相反，我需要返回一个类型化对象

这意味着我的代码需要更改为以下内容：

{
    "_id" : ObjectId("55d45c0285afc59c146f66f0"),
    "name" : "LG Nexus 6",
    "description" : "A Nexus 6 device, created by Google.",
    "typenr" : "LG-NEX-5/BLACK",
    "props" : [ 
        {
            "type" : "os",
            "value" : "Android"
        }, 
        {
            "type" : "storage",
            "value" : "8"
        }, 
        {
            "type" : "storage",
            "value" : "16"
        }, 
        {
            "type" : "storage",
            "value" : "32"
        }, 
        {
            "type" : "storage",
            "value" : "64"
        }
    ]
}

// Get all the amount of filters that are defined.
db.smartphones.aggregate([
    // Unwind the "props".
    { "$unwind" : "$props" },

    // Grouping phase.
    // Group by unique properties, add a count for the amount of articles, and add articles to an element named "articles".
    // We use the function "$addToSet" here to ensure that only unique articles are being added.
    { 
        "$group" : { 
            "_id" : "$props", 
            count : { "$sum" : 1 }, 
            articles: { 
                "$addToSet": { 
                    name: "$name", 
                    description: "$description", 
                    typenr: "$typenr" 
                } 
            } 
        } 
    },

    // Sort the results based on the "_id" field.
    { "$sort" : { "_id" : 1 } }
]);

"_id" : {
    "type" : "storage",
    "value" : "128"
},
"count" : 1.0000000000000000,
"articles" : [ 
    {
        "name" : "Apple iPhone 6",
        "description" : "An iPhone 6 device, created by Apple.",
        "typenr" : "APP-IPHONE-6/BLACK"
    }
]

// Get all the amount of filters that are defined.
db.smartphones.aggregate([
    // Unwind the "props".
    { "$unwind" : "$props" }, 

    // Grouping phase.
    // Group by unique properties, add a count for the amount of articles, and add articles to an element named "articles".
    // We use the function "$addToSet" here to ensure that only unique articles are being added.
    { 
        "$group" : { 
            "_id" : "$props", 
            "count" : { "$sum" : 1 }, 
            "articles" : { 
                "$addToSet" : { 
                    "name" : "$name", 
                    "description" : "$description", 
                    "typenr" : "$typenr" 
                } 
            } 
        } 
    }, 
    { "$sort" : { "_id" : 1 } }
])

var aggregation = collection.Aggregate()
    .Unwind<Smartphone, UnwindedSmartphone>(x => x.Properties)
    .Group(key => key.Property, g => new
    {
        Count = g.Count(),
        Articles = g.Select(x => new AggregatedSmartphoneArticle
        {
            Name = x.Name,
            Description = x.Description,
            Type = x.Type
        }).Distinct()
    });

var aggregation=collection.Aggregate（）
.展开（x=>x.Properties）
.Group（key=>key.Property，g=>new
{
Count=g.Count（），
Articles=g.Select（x=>newaggregatedSmartPhoneArticle
{
Name=x.Name，
描述=x.描述，
类型=x.类型
}).Distinct（）
});

现在一切正常。

---

再次感谢。使用键入的代码比使用那些

BsonDocument

要清楚得多，谢谢你的回答，但是什么应该把它们改成我的代码，因为它不太清楚。我看不出我需要在哪里指定输出类型。好吧，我正要在你的“it serializes like this”上调用“phooey”，但你显然刚刚发现你需要给它一个类来用lambda进行迭代。