[英]How to create a fluent Aggregation using MongoDB C# Driver 2.0
I'm quite new to MongoDB and I'm using it in a Web Api to serve a mobile application. 我是MongoDB的新手,我在Web Api中使用它来为移动应用程序提供服务。
Now, I need to run an aggregation and since I'm using C#, I would like to do it fluently by using the Aggregate
command on a collection which returns me an IAggregateFluent
. 现在,我需要运行一个聚合,因为我正在使用C#,我想通过在一个集合上使用Aggregate
命令来流利地执行它,该集合返回一个IAggregateFluent
。
However, I'm stuck and the information which I found here on SO doesn't help me, so therefore a new question. 但是,我被困住了,我在SO上找到的信息对我没有帮助,因此是一个新问题。
I've built a small collection that holds smartphones with some basic properties, and a single item in the smartphone collection does look like: 我已经建立了一个小型集合,其中包含具有一些基本属性的智能手机,智能手机集合中的单个项目看起来像:
{
"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"
}
]
}
Now, I've created an aggregation in the shell which looks like the following: 现在,我在shell中创建了一个聚合,如下所示:
// 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 } }
]);
And now I need to translate this to C#. 现在我需要将其转换为C#。
First, I do create the following (plain C# code, it just returns an IMongoCollection<Article>
). 首先,我创建了以下(纯C#代码,它只返回一个IMongoCollection<Article>
)。
var collection = context.ArticleRepository;
Here's the model which the collection does return: 这是集合确实返回的模型:
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
}
Now, I need to aggregate on this collection, and I'm strugling already with the basics: 现在,我需要在这个集合上进行聚合,而且我已经对基础知识进行了深入研究:
// Build the aggregation using the fluent api.
var aggregation = collection.Aggregate()
.Unwind(x => x.Properties)
.Group(x => new { x.Properties );
Right now, I only try to group on properties, like in the aggregation but this results in the following error: 现在,我只尝试对属性进行分组,就像在聚合中一样,但这会导致以下错误:
CS0411 The type arguments for method 'IAggregateFluent<BsonDocument>.Group<TNewResult>(ProjectionDefinition<BsonDocument, TNewResult>)' cannot be inferred from the usage. Try specifying the type arguments explicitly.
But even when that's working, I also need the extra properties as count
and addToSet
. 但即使它正在工作,我还需要额外的属性作为count
和addToSet
。 Can someone help me with this one. 有人可以帮助我这个。 I'm already searching for 2 days on this and it's driving me crazy. 我已经在这上面搜索了2天,这让我发疯了。
Edit 编辑
I've found that a group followed by an unwind does work in C#, but why doesn't it work with the unwind first? 我发现一个后续放松的小组确实在C#中工作,但为什么它不能先解开呢? I really need the unwind to happen first. 我真的需要先放松一下。
Edit 2 I've managed to get a small portion working, inclusive the group
command. 编辑2我设法让一小部分工作,包括group
命令。 See the code below: 请参阅以下代码:
var aggregation = collection.Aggregate()
.Unwind<Smartphone, UnwindedSmartphone>(x => x.Properties)
.Group(key => key.Property, g => new
{
Id = g.Key,
Count = g.Count()
});
However, I need some more information on how to push the Articles property from the aggregation command. 但是,我需要更多关于如何从聚合命令中推送Articles属性的信息。
I've found the solution to the problem. 我找到了问题的解决方案。 The following C# code should be used: 应使用以下C#代码:
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
}).Distinct()
})
.SortBy(x => x.Id);
This gives me the following aggregation: 这给了我以下聚合:
db.smartphones.aggregate([{ "$unwind" : "$props" }, { "$group" : { "_id" : "$props", "Count" : { "$sum" : 1 }, "Articles" : { "$addToSet" : { "Name" : "$name" } } } }, { "$sort" : { "_id" : 1 } }])
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