C# Distinct使用，支持对象的相等比较

最新推荐文章于 2022-11-11 11:22:18 发布

weixin_33805992

最新推荐文章于 2022-11-11 11:22:18 发布

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文章标签： c# 数据库

本文深入探讨了在C#中使用Distinct方法的高级用法，包括如何自定义比较器来实现更复杂的过滤逻辑，以及在不同上下文中的应用实例。

官网Enumerable.Distinct

https://msdn.microsoft.com/zh-cn/library/bb338049.aspx

优快云中作者oriency755

关于Distinct的使用：

http://blog.youkuaiyun.com/oriency755/article/details/13773557

使用

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data;
using System.Transactions;

namespace Activity
{
    public class ActivitySceneService
    {
        public List<DrawPlay> GetDraw(int activitySceneID)
        {
            using (var dbContext = new DbContext())
            {
                var merchant = dbContext.Find<Merchant>(1);
                var playList = new List<DrawPlay>();
                    playList = dbContext.Draw001Plays.Where(u => u.ActivitySceneID == activitySceneID).Distinct(
                        new Compare<DrawPlay>((x, y) => (x != null && y != null && x.UserID == y.UserID))).ToList();//放置比较器
                return playlist;
            }
        }
    }

    public delegate bool CompareDelegate<T>(T x, T y);
    public class Compare<T> : IEqualityComparer<T>
    {
        private CompareDelegate<T> _compare;
        public Compare(CompareDelegate<T> d)
        {
            this._compare = d;
        }

        public bool Equals(T x, T y)
        {
            if (_compare != null)
            {
                return this._compare(x, y);
            }
            else
            {
                return false;
            }
        }

        public int GetHashCode(T obj)
        {
            return obj.ToString().GetHashCode();
        }
    }
}

Test

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data;

namespace NAMESPACE
{
    public class CLASSNAME
    {
        public void Test()
        {
            using (var dbContext = new DbContext())
            {
                 dbContext.DATABASE.Distinct(
                        new Compare<MODELTYPE>((x, y) => (x != null && y != null && x.FIELD> VALUE && y.FIELD> VALUE))).ToList();
            }
        }
     }

//使用委托
    public delegate bool CompareDelegate<T>(T x, T y);
    public class Compare<T> : IEqualityComparer<T>
    {
        private CompareDelegate<T> _compare;
        public Compare(CompareDelegate<T> d)
        {
            this._compare = d;
        }

        public bool Equals(T x, T y)
        {
            if (_compare != null)
            {
                return this._compare(x, y);
            }
            else
            {
                return false;
            }
        }

        public int GetHashCode(T obj)
        {
            return obj.ToString().GetHashCode();
        }
    }
}

和上一个差不多

Distinct项目内使用

using Qxun.Framework.Utility

var onlineRecords = dbContext.OnLineRecords.ToList().Distinct(new CompareExtend<OnLineRecord>((x, y) => x != null && y != null && x.MerchantID == y.MerchantID && x.ActivitySceneID == y.ActivitySceneID));

****************************************CompareExtend类********************************************************

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

namespace Qxun.Framework.Utility
{
    public delegate bool CompareDelegate<T>(T x, T y);
    public class CompareExtend<T> : IEqualityComparer<T>
    {
        private CompareDelegate<T> _compare;
        public CompareExtend(CompareDelegate<T> d)
        {
            this._compare = d;
        }

        public bool Equals(T x, T y)
        {
            if (_compare != null)
            {
                return this._compare(x, y);
            }
            else
            {
                return false;
            }
        }

        public int GetHashCode(T obj)
        {
            return obj.ToString().GetHashCode();
        }
    }
}

distinct 项目中使用