LINQ：根据子列表中的属性进行分组

发布于 2024-10-21 19:16:03 字数 653 浏览 2 评论 0原文

我正在尝试使用 LINQ 创建基于元数据的文档分组列表，元数据是文档上的列表。

下面是我的对象结构的外观：

List<Document>
         --> List<Metadata>
                      --> Metadata has a name and a value property.

我想根据名称为 ID 的元数据标签对文档进行分组，并在 ID 属性的值相同的情况下对它们进行分组。

我尝试了这样的操作：

var x = response.Document
         .GroupBy(d => d.Metadata.Where(dc => dc.Name == DocProperty.ID)
         .Select(dc => dc.Value));

这会生成单个文档的列表，但不会按 ID 分组。

还考虑过选择一个不同的 ID 列表，然后循环遍历文档列表并查找与 ID 匹配的文档。这似乎是很大的开销，因为对于不同列表中的每个 ID，我每次都必须进入元数据列表并查找文档，并且必须对找到的多个项目进行额外检查，获取我需要的属性等

。关于如何让这个东西发挥作用的好主意？

原文

I'am trying to use LINQ to create a grouped list of documents based on metadata which is a list on the document.

Below is how my object structure looks:

List<Document>
         --> List<Metadata>
                      --> Metadata has a name and a value property.

I want to group the documents based on an metadata tag which has a name: ID and group them where the values for the ID property are the same.

I tried it like this:

var x = response.Document
         .GroupBy(d => d.Metadata.Where(dc => dc.Name == DocProperty.ID)
         .Select(dc => dc.Value));

This results in a list of single documents, but not grouped on ID.

Also thought about selecting a distinct list of ID's and then loop through the document list and find documents that match the ID. That one seems like a lot of overhead, because for every ID in the distinct list i have to go every time into the metadata list and find the documents and have to extra checks for multiple items found, get the property i need etc.

Anyone has a good idea about how to get this thing working?

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逆蝶 2024-10-28 19:16:03

var x = from doc in source
        from meta in doc.Metadata
        where meta.Name == DocProperty.Id
        group doc by meta.Value;

或者（注释）作为流畅的表示法：

var y = source
    .SelectMany(doc => doc.Metadata, (doc, meta) => new { doc, meta })
    .Where(pair => pair.meta.Name == DocProperty.Id)
    .GroupBy(pair => pair.meta.Value, pair => pair.doc);

var x = from doc in source
        from meta in doc.Metadata
        where meta.Name == DocProperty.Id
        group doc by meta.Value;

Or (comments) as fluent notation:

var y = source
    .SelectMany(doc => doc.Metadata, (doc, meta) => new { doc, meta })
    .Where(pair => pair.meta.Name == DocProperty.Id)
    .GroupBy(pair => pair.meta.Value, pair => pair.doc);

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