我对MongoDB还比较新,正在将其用于Web Api以为移动应用提供服务。
现在,我需要运行聚合操作,并且由于我使用C#,因此希望通过在集合上使用
但是,我遇到了问题,并且在这里找到的信息并没有帮助我,因此提出了新的问题。
我已经构建了一个小型集合,其中包含一些基本属性的智能手机,并且智能手机集合中的单个项如下:
现在,我需要对这个集合进行聚合操作,但已经在基础方面遇到了困难:
然而,我需要更多关于如何从聚合命令中推送文章属性的信息。
现在,我需要运行聚合操作,并且由于我使用C#,因此希望通过在集合上使用
Aggregate
命令来流畅地执行它,从而返回IAggregateFluent
。但是,我遇到了问题,并且在这里找到的信息并没有帮助我,因此提出了新的问题。
我已经构建了一个小型集合,其中包含一些基本属性的智能手机,并且智能手机集合中的单个项如下:
{
"name" : "LG Nexus 5",
"description" : "A Nexus 5 device, created by Google.",
"typenr" : "LG-NEX-5/WHITE",
"props" : [
{
"type" : "os",
"value" : "Android"
},
{
"type" : "storage",
"value" : "8"
},
{
"type" : "storage",
"value" : "16"
},
{
"type" : "storage",
"value" : "32"
},
{
"type" : "storage",
"value" : "64"
}
]
}
现在,我已经在shell中创建了一个聚合,它看起来像下面这样:
// 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"
} x =>
}
}
},
// Sort the results based on the "_id" field.
{ "$sort" : { "_id" : 1 } }
]);
现在我需要将这个内容翻译为C#代码。
首先,我创建了以下代码(纯C#代码,只返回一个IMongoCollection<Article>
)。
var collection = context.ArticleRepository;
这是集合返回的模型:
public class Article
{
#region Properties
/// <summary>
/// Unique identifier for the article.
/// </summary>
[BsonRepresentation(BsonType.ObjectId)]
public string Id { get; set; }
/// <summary>
/// Name of the article.
/// </summary>
[BsonElement("name")]
[BsonIgnoreIfNull]
[BsonIgnoreIfDefault]
public BsonString Name { get; set; }
/// <summary>
/// Name of the element but in lowercase.
/// </summary>
/// <remarks>
/// We'll create this field to enable text-search on this field without respecting capital letters.
/// </remarks>
[BsonElement("namelc")]
[BsonIgnoreIfNull]
[BsonIgnoreIfDefault]
public BsonString LowercaseName { get; set; }
/// <summary>
/// Specification of the article.
/// </summary>
[BsonElement("specification")]
[BsonIgnoreIfNull]
[BsonIgnoreIfDefault]
public BsonString Specificiation { get; set; }
/// <summary>
/// Brand of the article.
/// </summary>
[BsonElement("brand")]
[BsonIgnoreIfNull]
[BsonIgnoreIfDefault]
public BsonString Brand { get; set; }
/// <summary>
/// Supplier of the article.
/// </summary>
[BsonElement("supplier")]
[BsonIgnoreIfNull]
[BsonIgnoreIfDefault]
public Supplier Supplier { get; set; }
/// <summary>
/// Number of the article.
/// </summary>
[BsonElement("nr")]
[BsonIgnoreIfNull]
[BsonIgnoreIfDefault]
public BsonString ArticleNumber { get; set; }
/// <summary>
/// Gtin number of the article.
/// </summary>
[BsonElement("gtin")]
[BsonIgnoreIfNull]
[BsonIgnoreIfDefault]
public string ArticleGtin { get; set; }
/// <summary>
/// type number of the article.
/// </summary>
[BsonElement("typeNr")]
[BsonIgnoreIfNull]
[BsonIgnoreIfDefault]
public string TypeNumber { get; set; }
/// <summary>
/// Properties of the article.
/// </summary>
/// <remarks>
/// This field can be used to ensure that we can filter on the articles.
/// By default, this is an empty list, this avoids initialization logic.
/// </remarks>
[BsonElement("props")]
[BsonIgnoreIfNull]
[BsonIgnoreIfDefault]
public List<ArticleProperty> Properties { get; set; } = new List<ArticleProperty>();
#endregion
}
/// <summary>
/// Class representing a single supplier in the database.
/// </summary>
/// <remarks>
/// This class is not used as a "root" document inside our database.
/// Instead, it's being embedded into our "Articles" document.
/// </remarks>
public class Supplier
{
#region Properties
/// <summary>
/// Name of the supplier.
/// </summary>
[BsonElement("supplier")]
[BsonIgnoreIfNull]
[BsonIgnoreIfDefault]
public BsonString Name { get; set; }
/// <summary>
/// Gln of the supplier.
/// </summary>
[BsonElement("gln")]
[BsonIgnoreIfNull]
[BsonIgnoreIfDefault]
public BsonString Gln { get; set; }
#endregion
}
/// <summary>
/// Class representing a single property for an article in the database.
/// </summary>
/// <remarks>
/// This class is not used as a "root" document inside our database.
/// Instead, it's being embedded into our "Articles" document.
/// </remarks>
public class ArticleProperty
{
#region Properties
/// <summary>
/// Type of the property.
/// </summary>
[BsonElement("type")]
[BsonIgnoreIfNull]
[BsonIgnoreIfDefault]
public BsonString Type { get; set; }
/// <summary>
/// Value of the property.
/// </summary>
[BsonElement("value")]
[BsonIgnoreIfNull]
[BsonIgnoreIfDefault]
public BsonString Value { get; set; }
#endregion
}
现在,我需要对这个集合进行聚合操作,但已经在基础方面遇到了困难:
// Build the aggregation using the fluent api.
var aggregation = collection.Aggregate()
.Unwind(x => x.Properties)
.Group(x => new { x.Properties );
目前,我只尝试按属性进行分组,就像聚合一样,但这会导致以下错误:
CS0411 方法“IAggregateFluent<BsonDocument>.Group<TNewResult>(ProjectionDefinition<BsonDocument, TNewResult>)”的类型参数无法从使用中推断出。请尝试明确指定类型参数。
即使这样做可以工作,我还需要额外的属性,如count
和addToSet
。有人能帮我解决吗?我已经寻找了两天,这让我发疯了。
编辑
我发现在C#中,跟随unwind
的group
有效,但为什么先使用unwind
就不起作用了呢?我真的需要先执行unwind
。
编辑2
我设法使一小部分有效,包括group
命令。请参见以下代码:
var aggregation = collection.Aggregate()
.Unwind<Smartphone, UnwindedSmartphone>(x => x.Properties)
.Group(key => key.Property, g => new
{
Id = g.Key,
Count = g.Count()
});
然而,我需要更多关于如何从聚合命令中推送文章属性的信息。