C＃在做一个简单的数据库比较器时发生错误 [英] C# Errors when doing a simple datarow comparer

问题描述

我基本上是试图做一个自定义的数据记录比较器，一些小的东西，并保持简单。

I'm basically trying to do a custom datarow comparer, something small and to keep it simple.

基本上我试图比较列<$ c $在datatableA和 Mykey2 中，在datatableB中的c> Mykey1

Basically i'm trying to compare column Mykey1 in datatableA and Mykey2 in datatableB.

错误，我不知道为什么他们被抛出或如何纠正它们。是的，我知道我正在使用一个int循环并将其更改为一个字符串，但显然这只是一个实验室，是的，我会比较字符串。

I'm getting three errors, and i'm not sure why they are being thrown or how to correct them. And Yes I know i'm using a for int loop and changing it to a string, but obviously this is just a lab, and yes i will be comparing strings.

1. 不能将类型'int'隐式转换为'string'


2. ConsoleApplication2 .MyDataRowComparer'不实现接口成员'System.Collections.Generic.IEqualityComparer.GetHashCode（System.Data.DataRow）


3. ConsoleApplication2.MyDataRowComparer'不实现接口成员'System.Collections'。 Generic.IEqualityComparer.Equals（System.Data.DataRow，System.Data.DataRow）

这里是代码

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

namespace ConsoleApplication2
{
    class Program
    {
        static void Main(string[] args)
        {
            DataTable DT1 = dt1();
            DataTable DT2 = dt2();
            IEnumerable<DataRow> idrP = DT1.AsEnumerable();
            IEnumerable<DataRow> idrS = DT2.AsEnumerable();

            MyDataRowComparer MyComparer = new MyDataRowComparer();
            IEnumerable<DataRow> Results = idrS.Except(idrP, MyComparer);
        }



        private static DataTable dt1()
        {
            DataTable DT1 = new DataTable();
            DT1.Columns.Add("Mykey1");
            for (int i = 0; i < 10000; i++)
            {
                DataRow newRow = DT1.NewRow();
                newRow[0] = i.ToString();
                DT1.Rows.Add(newRow);
            }

            return DT1;

        }


        private static DataTable dt2()
        {
            DataTable DT2 = new DataTable();
            DT2.Columns.Add("Mykey2");
            for (int i = 0; i < 20000; i++)
            {
                DataRow newRow = DT2.NewRow();
                newRow[0] = i.ToString();
                DT2.Rows.Add(newRow);
            }

            return DT2;

        }
    }

    public class MyDataRowComparer : IEqualityComparer<DataRow>`
    {
        public string Compare(DataRow x, DataRow y)
        {
            return String.Compare(x.Field<string>("Mykey1"), y.Field<string>("Mykey2"));
        }
    }
}

---

编辑

这是我的新DataRowComparer，但是它没有返回任何结果，而是获得

---

EDIT

Here is my new DataRowComparer, however it's not returning any results instead i get

{索引不在数组的边界。}

public class DataRowComparer : IEqualityComparer
    {
        public bool Equals(DataRow x, DataRow y)
        {
            return
             x.ItemArray.Except(new object[] { x["Mykey1"] }) ==
             y.ItemArray.Except(new object[] { y["Mykey2"] });
        }

        public int GetHashCode(DataRow obj)
        {
            var values = obj.ItemArray.Except(new object[] { obj[obj.Table.PrimaryKey[0].ColumnName] });
            int hash = 0;
            foreach (var value in values)
            {
                hash = (hash * 397) ^ value.GetHashCode();
            }
            return hash;
        }
    }

推荐答案

比较返回整数而不是字符串，因此您需要更改Compare方法签名。
这应该会解决第一个错误。

String.Compare returns an integer and not a string so you need to change your Compare method signature. That should resolve the first error.

其余的错误是由于您的类中缺少所需的实现，因为错误提示您缺少 System.Collections.Generic.IEqualityComparer.GetHashCode（System.Data.DataRow）方法和 System.Collections.Generic.IEqualityComparer.Equals （System.Data.DataRow，System.Data.DataRow）方法。

The rest of your errors are due to the fact your are missing needed implementations in your classes, as the error suggest you are missing the System.Collections.Generic.IEqualityComparer.GetHashCode(System.Data.DataRow) method and the System.Collections.Generic.IEqualityComparer.Equals(System.Data.DataRow, System.Data.DataRow) method.

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