当键和值是不同的子集时，查询子集--linq。

Question

我不能像下面这样查询一个集合，以获得给定 "key "的最大 "value"，但key和value是一个集合的子集合。

我需要得到这个集合的 "Revision "键的最大值。

- document 
    - id
    - description
    - key
        - version
        - revision
        - otherkey
    - value
        - "1.0"
        - 1
        - "othervalue"
- document 
    - id
    - description
    - key
        - version
        - revision
        - otherkey
    - value
        - "1.0"
        - 2
        - "othervalue"
- document 
    - id
    - description
    - key
        - version
        - revision
        - otherkey
    - value
        - "1.0"
        - 3
        - "othervalue"
- document 
    - id
    - description
    - key
        - version
        - revision
        - otherkey
    - value
        - "2.0"
        - 1
        - "othervalue"

有什么提示吗？

Answer 1

使用linq Zip函数可以将这两个子数组合并为一个。下面是一个获取每个版本的最大修订值的例子。

void Main()
{
    var data = GetData();

    var maxRevisions = data
        .Select(x => new { Document = x, KeyValue = x.Key.Zip(x.Value, (k, v) => new { Key = k, Value = v }) })
        .GroupBy(x => new { Version = x.KeyValue.First(kv => kv.Key == "version").Value })
        .Select(x => new { Version = x.Key.Version, MaxRevision = x.Max(y => y.KeyValue.First(kv => kv.Key == "revision").Value) })
        .ToList();


    maxRevisions.ForEach(mr => Console.WriteLine($"Version: {mr.Version} - MaxRevision: {mr.MaxRevision}"));
}

public class Document
{
    public int Id { get; set; }
    public string Description { get; set; }
    public List<String> Key { get; set; }
    public List<String> Value { get; set; }
}

public static List<Document> GetData()
{
    return new List<Document> {
        new Document {
            Id = 1,
            Description = "one-one",
            Key = new List<string> { "version", "revision", "otherkey" },
            Value = new List<string> { "1.0", "1", "othervalue" }
        },
        new Document {
            Id = 1,
            Description = "one-two",
            Key = new List<string> { "version", "revision", "otherkey" },
            Value = new List<string> { "1.0", "2", "othervalue" }
        },
        new Document {
            Id = 1,
            Description = "one-three",
            Key = new List<string> { "version", "revision", "otherkey" },
            Value = new List<string> { "1.0", "3", "othervalue" }
        },
        new Document {
            Id = 1,
            Description = "two-one",
            Key = new List<string> { "version", "revision", "otherkey" },
            Value = new List<string> { "2.0", "1", "othervalue" }
        }};
}

这将输出以下结果：

Version: 1.0 - MaxRevision: 3
Version: 2.0 - MaxRevision: 1