使用Linq进行包含IN的子查询并按指定字段分组统计代码,C#代码库,德仔网

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【C#】使用Linq进行包含IN的子查询并按指定字段分组统计

作者:雷霆 / 发布于2017/3/16/ 647

using System;
using System.Collections.Generic;
using System.Linq;

namespace ConsoleApplication2
{

    public class Program
    {
        static void Main(string[] args)
        {
            var includeKnowledgeIds = new List<KnowledgeBase> {
                new KnowledgeBase { KnowledgeId=1},
                new KnowledgeBase { KnowledgeId=2},
                new KnowledgeBase { KnowledgeId=3},
                new KnowledgeBase { KnowledgeId=5}
            };
            var questions = new List<Question> {
                new Question { Id=1,KnowledgeId=1},
                new Question { Id=2,KnowledgeId=2},
                new Question { Id=3,KnowledgeId=3},
                new Question { Id=4,KnowledgeId=1},
                new Question { Id=5,KnowledgeId=2},
                new Question { Id=6,KnowledgeId=4}
            };
            var query = from q in questions
                        where (
                            from i in includeKnowledgeIds
                            select i.KnowledgeId
                        ).ToList().Contains(q.KnowledgeId)
                        group q by q.KnowledgeId into questionGroup
                        select new
                        {
                            Key = questionGroup.Key,
                            Count = questionGroup.Count()
                        };
            query.ToList().ForEach(x =>
            {
                Console.WriteLine("KnowledgeId:{0}==>>Count:{1}", x.Key, x.Count);
            });
            Console.ReadKey();
        }
    }

    public class Question
    {
        public int Id { get; set; }
        public int KnowledgeId { get; set; }
    }

    public class KnowledgeBase
    {
        public int KnowledgeId { get; set; }
    }
}

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