一、原理與環境

在生成資料表的實體類時，利用自定義特性，給它打上表及欄位的特性，然後使用反射原理，將自定義特性拼接成增、刪、改、查對應的SQL，即可完成一個簡單的ORM。

本示例的執行環境：

1）資料庫：SQL Server。（可根據自己的需要，建立不同的資料庫工廠。）

2）資料表：需使用自增型別(identity)作為資料表的主鍵。主鍵名字可以隨便起，如ID。

3）實體類：實體類需提供無參建構函式。

二、演示資料表

Person表，包含主鍵（ID）、姓名（Name）、年齡（Age）、性別（Gender）。

CREATE TABLE [dbo].[Person](
    [ID] [BIGINT] IDENTITY(1,1) NOT NULL,[Name] [NVARCHAR](50) NULL,[Age] [INT] NULL,[Gender] [NVARCHAR](10) NULL,CONSTRAINT [PK_Person] PRIMARY KEY CLUSTERED 
(
    [ID] ASC
)WITH (PAD_INDEX = OFF,STATISTICS_NORECOMPUTE = OFF,IGNORE_DUP_KEY = OFF,ALLOW_ROW_LOCKS =
 
 ON,ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]

二、自定義特性

定義兩個自定義特性：

2.1、DataTableAttribute

此為資料表特性，包含表名（TableName）、主鍵（Key）。

    [Serializable]
    public class DataTableAttribute : Attribute
    {
        /// <summary>
        /// 資料表
        /// </summary>
        public
 
 string TableName { get; }

        /// <summary>
        /// 主鍵
        /// </summary>
        public string Key { get; }

        /// <summary>
        /// 建構函式
        /// </summary>
        /// <param name="tableName"></param>
        /// <param name="key"></param>
        public DataTableAttribute(string tableName,string key)
        {
            TableName = tableName;
            Key = key;
        }
    }

2.2、DataFieldAttribute

此為欄位特性，包含欄位名（FieldName）、欄位型別（FieldType）、長度（Length）、是否自增（IsIdentity）。

    [Serializable]
    public class DataFieldAttribute : Attribute
    {
        public string FieldName { get; set; }
        public string FieldType { get; set; }
        public int Length { get; set; }
        public bool IsIdentity { get; set; }

        /// <summary>
        /// 建構函式
        /// </summary>
        /// <param name="fieldName">欄位名</param>
        /// <param name="fieldType">欄位型別</param>
        /// <param name="length">長度</param>
        /// <param name="isIdentity">是否自增長</param>
        public DataFieldAttribute(string fieldName,string fieldType,int length,bool isIdentity)
        {
            FieldName = fieldName;
            FieldType = fieldType;
            Length = length;
            IsIdentity = isIdentity;
        }

        /// <summary>
        /// 建構函式
        /// </summary>
        /// <param name="fieldName"></param>
        /// <param name="length"></param>
        /// <param name="isIdentity"></param>
        public DataFieldAttribute(string fieldName,int length) : this(fieldName,fieldType,length,false)
        { }

        /// <summary>
        /// 建構函式
        /// </summary>
        /// <param name="fieldName"></param>
        /// <param name="fieldtype"></param>
        public DataFieldAttribute(string fieldName,string fieldType) : this(fieldName,0,false)
        { }

        /// <summary>
        /// 建構函式
        /// </summary>
        /// <param name="fieldName"></param>
        /// <param name="isIdentity"></param>
        public DataFieldAttribute(string fieldName,bool isIdentity) : this(fieldName,"",0,isIdentity)
        { }

        /// <summary>
        /// 建構函式
        /// </summary>
        /// <param name="fieldName"></param>
        public DataFieldAttribute(string fieldName) : this(fieldName,false)
        { }
    }

三、生成實體類

3.1、實體類樣式

依照前面的規劃，Person表需要生成下面這個樣子：

using System;
using System.Collections.Generic;
using System.Text;
using LinkTo.ORM.CustomAttribute;

namespace LinkTo.ORM.Model
{
    [DataTable("Person","ID")]
    [Serializable]
    public class Person
    {
        public Person() { }

        [DataField("ID","bigint",19,true)]
        public long? ID {get; set;}

        [DataField("Name","nvarchar",50,false)]
        public string Name {get; set;}

        [DataField("Age","int",10,false)]
        public int? Age {get; set;}

        [DataField("Gender",false)]
        public string Gender {get; set;}
    }
}

3.2、使用T4模板生成實體類

3.2.1、T4Code資料夾的文字模板

<#@ assembly name="System.Core" #>
<#@ assembly name="System.Data" #>
<#@ import namespace="System.Linq" #>
<#@ import namespace="System.Text" #>
<#@ import namespace="System.Collections.Generic" #>
<#@ import namespace="System.Data"#>
<#@ import namespace="System.Data.SqlClient"#>
<#+
    #region T4Code
    /// <summary>
    /// 資料庫架構介面
    /// </summary>
    public interface IDBSchema : IDisposable
    {
        List<string> GetTableList();
        DataTable GetTableMetadata(string tableName);
    }

    /// <summary>
    /// 資料庫架構工廠
    /// </summary>
    public class DBSchemaFactory
    {
        static readonly string DatabaseType = "SqlServer";
        public static IDBSchema GetDBSchema()
        {
            IDBSchema dbSchema;
            switch (DatabaseType) 
            {
                case "SqlServer":
                    {
                        dbSchema =new SqlServerSchema();
                        break;
                    }
                default: 
                    {
                        throw new ArgumentException("The input argument of DatabaseType is invalid.");
                    }
            }
            return dbSchema;
        }
    }

    /// <summary>
    /// SqlServer
    /// </summary>
    public class SqlServerSchema : IDBSchema
    {
        public string ConnectionString = "Server=.;Database=Test;Uid=sa;Pwd=********;";
        public SqlConnection conn;

        public SqlServerSchema()
        {
            conn = new SqlConnection(ConnectionString);
            conn.Open();
        }

        public List<string> GetTableList()
        {
            List<string> list = new List<string>();
            string commandText = "SELECT NAME TABLE_NAME FROM SYSOBJECTS WHERE XTYPE=‘U‘ ORDER BY NAME";

            using(SqlCommand cmd = new SqlCommand(commandText,conn))
            {
                using (SqlDataReader dr = cmd.ExecuteReader(CommandBehavior.CloseConnection))
                {
                    while (dr.Read())
                    {
                        list.Add(dr["TABLE_NAME"].ToString());
                    }
                }
            }

            return list;
        }
        
        public DataTable GetTableMetadata(string tableName)
        {
            string commandText=string.Format
                (
                    "SELECT A.NAME TABLE_NAME,B.NAME FIELD_NAME,C.NAME DATATYPE,ISNULL(B.PREC,0) LENGTH,"+
                        "CONVERT(BIT,CASE WHEN NOT F.ID IS NULL THEN 1 ELSE 0 END) ISKEY,CASE WHEN COLUMNPROPERTY(B.ID,B.NAME,‘ISIDENTITY‘) = 1 THEN 1 ELSE 0 END) AS ISIDENTITY,B.ISNULLABLE) ISNULLABLE "+
                    "FROM SYSOBJECTS A INNER JOIN SYSCOLUMNS B ON A.ID=B.ID INNER JOIN SYSTYPES C ON B.XTYPE=C.XUSERTYPE "+
                        "LEFT JOIN SYSOBJECTS D ON B.ID=D.PARENT_OBJ AND D.XTYPE=‘PK‘ "+
                        "LEFT JOIN SYSINDEXES E ON B.ID=E.ID AND D.NAME=E.NAME "+
                        "LEFT JOIN SYSINDEXKEYS F ON B.ID=F.ID AND B.COLID=F.COLID AND E.INDID=F.INDID "+
                    "WHERE A.XTYPE=‘U‘ AND A.NAME=‘{0}‘ "+
                    "ORDER BY A.NAME,B.COLORDER",tableName
                );

            using(SqlCommand cmd = new SqlCommand(commandText,conn))
            {
                SqlDataAdapter da = new SqlDataAdapter(cmd);
                DataSet ds = new DataSet();
                da.Fill(ds,"Schema");
                return ds.Tables[0];
            }
        }

        public void Dispose()
        {
            if (conn != null)
            {
                conn.Close();
            }
        }
    }
    #endregion
#>

<#@ assembly name="System.Core" #>
<#@ assembly name="System.Data" #>
<#@ assembly name="EnvDTE" #>
<#@ import namespace="System.Linq" #>
<#@ import namespace="System.Text" #>
<#@ import namespace="System.Collections.Generic" #>
<#@ import namespace="System.Data"#>
<#@ import namespace="System.IO"#>
<#@ import namespace="Microsoft.VisualStudio.TextTemplating"#>

<#+
// T4 Template Block manager for handling multiple file outputs more easily.
// Copyright (c) Microsoft Corporation.All rights reserved.
// This source code is made available under the terms of the Microsoft Public License (MS-PL)

// Manager class records the various blocks so it can split them up
class Manager
{
    public struct Block
    {
        public string Name;
        public int Start,Length;
    }

    public List<Block> blocks = new List<Block>();
    public Block currentBlock;
    public Block footerBlock = new Block();
    public Block headerBlock = new Block();
    public ITextTemplatingEngineHost host;
    public ManagementStrategy strategy;
    public StringBuilder template;
    public string OutputPath { get; set; }

    public Manager(ITextTemplatingEngineHost host,StringBuilder template,bool commonHeader)
    {
        this.host = host;
        this.template = template;
        OutputPath = string.Empty;
        strategy = ManagementStrategy.Create(host);
    }

    public void StartBlock(string name)
    {
        currentBlock = new Block { Name = name,Start = template.Length };
    }

    public void StartFooter()
    {
        footerBlock.Start = template.Length;
    }

    public void EndFooter()
    {
        footerBlock.Length = template.Length - footerBlock.Start;
    }

    public void StartHeader()
    {
        headerBlock.Start = template.Length;
    }

    public void EndHeader()
    {
        headerBlock.Length = template.Length - headerBlock.Start;
    }    

    public void EndBlock()
    {
        currentBlock.Length = template.Length - currentBlock.Start;
        blocks.Add(currentBlock);
    }

    public void Process(bool split)
    {
        string header = template.ToString(headerBlock.Start,headerBlock.Length);
        string footer = template.ToString(footerBlock.Start,footerBlock.Length);
        blocks.Reverse();
        foreach(Block block in blocks) {
            string fileName = Path.Combine(OutputPath,block.Name);
            if (split) {
                string content = header + template.ToString(block.Start,block.Length) + footer;
                strategy.CreateFile(fileName,content);
                template.Remove(block.Start,block.Length);
            } else {
                strategy.DeleteFile(fileName);
            }
        }
    }
}

class ManagementStrategy
{
    internal static ManagementStrategy Create(ITextTemplatingEngineHost host)
    {
        return (host is IServiceProvider) ? new VSManagementStrategy(host) : new ManagementStrategy(host);
    }

    internal ManagementStrategy(ITextTemplatingEngineHost host) { }

    internal virtual void CreateFile(string fileName,string content)
    {
        File.WriteAllText(fileName,content);
    }

    internal virtual void DeleteFile(string fileName)
    {
        if (File.Exists(fileName))
            File.Delete(fileName);
    }
}

class VSManagementStrategy : ManagementStrategy
{
    private EnvDTE.ProjectItem templateProjectItem;

    internal VSManagementStrategy(ITextTemplatingEngineHost host) : base(host)
    {
        IServiceProvider hostServiceProvider = (IServiceProvider)host;
        if (hostServiceProvider == null)
            throw new ArgumentNullException("Could not obtain hostServiceProvider");

        EnvDTE.DTE dte = (EnvDTE.DTE)hostServiceProvider.GetService(typeof(EnvDTE.DTE));
        if (dte == null)
            throw new ArgumentNullException("Could not obtain DTE from host");

        templateProjectItem = dte.Solution.FindProjectItem(host.TemplateFile);
    }

    internal override void CreateFile(string fileName,string content)
    {
        base.CreateFile(fileName,content);
        ((EventHandler)delegate { templateProjectItem.ProjectItems.AddFromFile(fileName); }).BeginInvoke(null,null,null);
    }

    internal override void DeleteFile(string fileName)
    {
        ((EventHandler)delegate { FindAndDeleteFile(fileName); }).BeginInvoke(null,null);
    }

    private void FindAndDeleteFile(string fileName)
    {
        foreach(EnvDTE.ProjectItem projectItem in templateProjectItem.ProjectItems)
        {
            if (projectItem.get_FileNames(0) == fileName)
            {
                projectItem.Delete();
                return;
            }
        }
    }
}
#>

DBSchema.ttinclude主要實現了資料庫工廠的功能。注：請將資料庫連線字串改成您自己的。

MultiDocument.ttinclude主要實現了多文件的功能。

3.2.2、生成實體類的文字模板

<#@ template debug="true" hostspecific="true" language="C#" #>
<#@ assembly name="System.Core" #>
<#@ import namespace="System.Linq" #>
<#@ import namespace="System.Text" #>
<#@ import namespace="System.Collections.Generic" #>
<#@ output extension=".cs" #>
<#@ include file="T4Code/DBSchema.ttinclude"#>
<#@ include file="T4Code/MultiDocument.ttinclude"#>
<# var manager = new Manager(Host,GenerationEnvironment,true) { OutputPath = Path.GetDirectoryName(Host.TemplateFile)}; #>
<#
    //System.Diagnostics.Debugger.Launch();//除錯
    var dbSchema = DBSchemaFactory.GetDBSchema();
    List<string> tableList = dbSchema.GetTableList();
    foreach (string tableName in tableList)
    {
        manager.StartBlock(tableName+".cs");
        DataTable table = dbSchema.GetTableMetadata(tableName);

        //獲取主鍵
        string strKey = string.Empty;
        foreach (DataRow dataRow in table.Rows)
        {
            if ((bool)dataRow["ISKEY"] == true)
            {
                strKey = dataRow["FIELD_NAME"].ToString();
                break;
            }
        }
        
#>
//-------------------------------------------------------------------------------
// 此程式碼由T4模板MultModelAuto自動生成
// 生成時間 <#= DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss") #>
// 對此檔案的更改可能會導致不正確的行為，並且如果重新生成程式碼，這些更改將會丟失。
//-------------------------------------------------------------------------------

using System;
using System.Collections.Generic;
using System.Text;
using LinkTo.ORM.CustomAttribute;

namespace LinkTo.ORM.Model
{
    [DataTable("<#= tableName #>","<#= strKey #>")]
    [Serializable]
    public class <#= tableName #>
    {
        public <#= tableName #>() { }
<#
        foreach (DataRow dataRow in table.Rows)
        {
            //獲取資料型別
            string dbDataType = dataRow["DATATYPE"].ToString();
            string dataType = string.Empty;
                    
            switch (dbDataType)
            {
                case "decimal":
                case "numeric":
                case "money":
                case "smallmoney":
                    dataType = "decimal?";
                    break;
                case "char":
                case "nchar":
                case "varchar":
                case "nvarchar":
                case "text":
                case "ntext":
                    dataType = "string";
                    break;
                case "uniqueidentifier":
                    dataType = "Guid?";
                    break;
                case "bit":
                    dataType = "bool?";
                    break;
                case "real":
                    dataType = "Single?";
                    break;
                case "bigint":
                    dataType = "long?";
                    break;
                case "int":
                    dataType = "int?";
                    break;
                case "tinyint":
                case "smallint":
                    dataType = "short?";
                    break;
                case "float":
                    dataType = "float?";
                    break;
                case "date":
                case "datetime":
                case "datetime2":
                case "smalldatetime":
                    dataType = "DateTime?";
                    break;
                case "datetimeoffset ":
                    dataType = "DateTimeOffset?";
                    break;
                case "timeSpan ":
                    dataType = "TimeSpan?";
                    break;
                case "image":
                case "binary":
                case "varbinary":
                    dataType = "byte[]";
                    break;
                default:
                    break;
            }
#>

        [DataField("<#= dataRow["FIELD_NAME"].ToString() #>","<#= dataRow["DATATYPE"].ToString() #>",<#= dataRow["LENGTH"].ToString() #>,<#= dataRow["ISIDENTITY"].ToString().ToLower() #>)]
        public <#= dataType #> <#= dataRow["FIELD_NAME"].ToString() #> {get; set;}
<#
        }
#>
    }
}
<#
        manager.EndBlock();
    }
    dbSchema.Dispose();
    manager.Process(true);
#>

注：由於ORM拼接SQL時使用的是表特性及欄位特性，可以看出表特性上使用的表名、欄位特性上使用的欄位名，都是與資料庫一致的。有了這個保障，資料表生成實體類的時候，類名是可以更改的，因為我只需要保證表特性與資料庫一致即可。舉個例子，我有個資料表Person_A，在生成實體類時，類名可以生成為Class PersonA {...}，但是表特性依然是[DataTable("Person_A","...")]。相同的原理，屬性名也是可以更改的。

四、ORM實現

資料表的CURD，主要是通過反射來實現SQL拼接，實現如下：

using System;
using System.Collections;
using System.Collections.Generic;
using System.Data;
using System.Data.SqlClient;
using System.Linq;
using System.Reflection;
using System.Text;
using System.Threading.Tasks;
using LinkTo.ORM.CustomAttribute;

namespace LinkTo.ORM
{
    public static class DBHelper
    {
        public static readonly string ConnectionString = "Server=.;Database=Test;Uid=sa;Pwd=********;";
        private static readonly Hashtable _HashTableName = new Hashtable(); //表名快取
        private static readonly Hashtable _HashKey = new Hashtable();       //主鍵快取

        /// <summary>
        /// 資料庫連線
        /// </summary>
        /// <returns></returns>
        public static SqlConnection GetConnection()
        {
            SqlConnection conn = new SqlConnection(ConnectionString);
            return conn;
        }

        /// <summary>
        /// 新增
        /// </summary>
        /// <typeparam name="TEntity"></typeparam>
        /// <param name="entity"></param>
        /// <returns></returns>
        public static int Insert<TEntity>(TEntity entity) where TEntity : class
        {
            string strTableName = "";                                   //表名
            string strInsertSQL = "INSERT INTO {0} ({1}) VALUES ({2})"; //SQL拼接語句

            //獲取表名
            strTableName = GetTableName(entity);

            //獲取欄位列表及值列表
            StringBuilder strFields = new StringBuilder();
            StringBuilder strValues = new StringBuilder();
            List<SqlParameter> paraList = new List<SqlParameter>();

            PropertyInfo[] infos = entity.GetType().GetProperties();
            DataFieldAttribute dfAttr = null;
            object[] dfAttrs;

            int i = 0;
            foreach (PropertyInfo info in infos)
            {
                dfAttrs = info.GetCustomAttributes(typeof(DataFieldAttribute),false);
                if (dfAttrs.Length > 0)
                {
                    dfAttr = dfAttrs[0] as DataFieldAttribute;
                    if (dfAttr is DataFieldAttribute)
                    {
                        //自增欄位不作處理
                        if (dfAttr.IsIdentity) continue;

                        strFields.Append(i > 0 ? "," + dfAttr.FieldName : dfAttr.FieldName);
                        strValues.Append(i > 0 ? "," + "@" + dfAttr.FieldName : "@" + dfAttr.FieldName);
                        i++;
                        paraList.Add(new SqlParameter("@" + dfAttr.FieldName,info.GetValue(entity,null)));
                    }
                }
            }

            //格式化SQL拼接語句
            string[] args = new string[] { strTableName,strFields.ToString(),strValues.ToString() };
            strInsertSQL = string.Format(strInsertSQL,args);

            //執行結果
            int result = 0;
            try
            {
                using (SqlConnection conn = GetConnection())
                {
                    conn.Open();
                    using (SqlCommand cmd = new SqlCommand())
                    {
                        cmd.CommandText = strInsertSQL;
                        cmd.CommandType = CommandType.Text;
                        cmd.Connection = conn;
                        if (paraList != null)
                        {
                            foreach (SqlParameter param in paraList)
                            {
                                cmd.Parameters.Add(param);
                            }
                        }
                        result = cmd.ExecuteNonQuery();
                    }
                }
            }
            catch (Exception ex)
            {
                throw new Exception(ex.ToString());
            }

            //返回影響行數
            return result;
        }

        /// <summary>
        /// 刪除
        /// </summary>
        /// <typeparam name="TEntity"></typeparam>
        /// <param name="condition"></param>
        /// <returns></returns>
        public static int Delete<TEntity>(string condition) where TEntity : class,new()
        {
            string strTableName = "";                           //表名
            string strDeleteSQL = "DELETE FROM {0} WHERE {1}";  //SQL拼接語句

            //獲取表名
            strTableName = GetTableName(new TEntity());

            //格式化SQL拼接語句
            string[] args = new string[] { strTableName,condition };
            strDeleteSQL = string.Format(strDeleteSQL,args);

            //執行結果
            int result = 0;
            try
            {
                using (SqlConnection conn = GetConnection())
                {
                    conn.Open();
                    using (SqlCommand cmd = new SqlCommand())
                    {
                        cmd.CommandText = strDeleteSQL;
                        cmd.CommandType = CommandType.Text;
                        cmd.Connection = conn;
                        result = cmd.ExecuteNonQuery();
                    }
                }
            }
            catch (Exception ex)
            {
                throw new Exception(ex.ToString());
            }

            //返回影響行數
            return result;
        }

        /// <summary>
        /// 更新
        /// </summary>
        /// <typeparam name="TEntity"></typeparam>
        /// <param name="entity"></param>
        /// <returns></returns>
        public static int Update<TEntity>(TEntity entity) where TEntity : class
        {
            string strTableName = "";                               //表名
            string strUpdateSQL = "UPDATE {0} SET {1} WHERE {2}";   //SQL拼接語句
            string strKey = "";                                     //主鍵
            string strWhere = "";                                   //條件

            //獲取表名及主鍵
            strTableName = GetTableName(entity);
            strKey = GetKey(entity);

            //獲取更新列表
            StringBuilder strSET = new StringBuilder();
            List<SqlParameter> paraList = new List<SqlParameter>();

            PropertyInfo[] infos = entity.GetType().GetProperties();
            DataFieldAttribute dfAttr = null;
            object[] dfAttrs;

            int i = 0;
            foreach (PropertyInfo info in infos)
            {
                dfAttrs = info.GetCustomAttributes(typeof(DataFieldAttribute),false);
                if (dfAttrs.Length > 0)
                {
                    dfAttr = dfAttrs[0] as DataFieldAttribute;
                    if (dfAttr is DataFieldAttribute)
                    {
                        //條件處理
                        if (dfAttr.FieldName == strKey)
                        {
                            strWhere = strKey + "=" + info.GetValue(entity,null);
                        }

                        //自增欄位不作處理
                        if (dfAttr.IsIdentity) continue;

                        strSET.Append(i > 0 ? "," + dfAttr.FieldName + "[email protected]" + dfAttr.FieldName : dfAttr.FieldName + "[email protected]" + dfAttr.FieldName);
                        i++;
                        paraList.Add(new SqlParameter("@" + dfAttr.FieldName,strSET.ToString(),strWhere };
            strUpdateSQL = string.Format(strUpdateSQL,args);

            //執行結果
            int result = 0;
            try
            {
                using (SqlConnection conn = GetConnection())
                {
                    conn.Open();
                    using (SqlCommand cmd = new SqlCommand())
                    {
                        cmd.CommandText = strUpdateSQL;
                        cmd.CommandType = CommandType.Text;
                        cmd.Connection = conn;
                        if (paraList != null)
                        {
                            foreach (SqlParameter param in paraList)
                            {
                                cmd.Parameters.Add(param);
                            }
                        }
                        result = cmd.ExecuteNonQuery();
                    }
                }
            }
            catch (Exception ex)
            {
                throw new Exception(ex.ToString());
            }

            //返回影響行數
            return result;
        }

        /// <summary>
        /// 查詢
        /// </summary>
        /// <typeparam name="TEntity"></typeparam>
        /// <param name="condition"></param>
        /// <returns></returns>
        public static List<TEntity> Query<TEntity>(string condition) where TEntity : class,new()
        {
            string strTableName = "";                               //表名
            string strSelectSQL = "SELECT * FROM {0} WHERE {1}";    //SQL拼接語句
            List<TEntity> list = new List<TEntity>();               //實體列表

            //獲取表名
            strTableName = GetTableName(new TEntity());

            //格式化SQL拼接語句
            string[] args = new string[] { strTableName,condition };
            strSelectSQL = string.Format(strSelectSQL,args);

            //獲取實體列表
            PropertyInfo[] infos = typeof(TEntity).GetProperties();
            DataFieldAttribute dfAttr = null;
            object[] dfAttrs;
            try
            {
                using (SqlConnection conn = GetConnection())
                {
                    conn.Open();
                    using (SqlCommand cmd = new SqlCommand(strSelectSQL,conn))
                    {
                        using (SqlDataReader dr = cmd.ExecuteReader(CommandBehavior.CloseConnection))
                        {
                            while (dr.Read())
                            {
                                TEntity entity = new TEntity();
                                foreach (PropertyInfo info in infos)
                                {
                                    dfAttrs = info.GetCustomAttributes(typeof(DataFieldAttribute),false);
                                    if (dfAttrs.Length > 0)
                                    {
                                        dfAttr = dfAttrs[0] as DataFieldAttribute;

                                        if (dfAttr is DataFieldAttribute)
                                        {
                                            info.SetValue(entity,dr[dfAttr.FieldName]);
                                        }
                                    }
                                }
                                list.Add(entity);
                            }
                        }
                    }
                }
            }
            catch (Exception ex)
            {
                throw new Exception(ex.ToString());
            }

            //返回實體列表
            return list;
        }

        /// <summary>
        /// 根據實體返回表名
        /// </summary>
        /// <param name="entity"></param>
        /// <returns></returns>
        public static string GetTableName<TEntity>(TEntity entity) where TEntity : class
        {
            Type entityType = entity.GetType();
            string strTableName = Convert.ToString(_HashTableName[entityType.FullName]);

            if (strTableName == "")
            {
                if (entityType.GetCustomAttributes(typeof(DataTableAttribute),false)[0] is DataTableAttribute dtAttr)
                {
                    strTableName = dtAttr.TableName;
                }
                else
                {
                    throw new Exception(entityType.ToString() + "未設定DataTable特性。");
                }

                _HashTableName[entityType.FullName] = strTableName;
            }

            return strTableName;
        }

        /// <summary>
        /// 根據實體返回主鍵
        /// </summary>
        /// <param name="entity"></param>
        /// <returns></returns>
        public static string GetKey<TEntity>(TEntity entity) where TEntity : class
        {
            Type entityType = entity.GetType();
            string strKey = Convert.ToString(_HashKey[entityType.FullName]);

            if (strKey == "")
            {
                if (entityType.GetCustomAttributes(typeof(DataTableAttribute),false)[0] is DataTableAttribute dtAttr)
                {
                    strKey = dtAttr.Key;
                }
                else
                {
                    throw new Exception(entityType.ToString() + "未設定DataTable特性。");
                }

                _HashKey[entityType.FullName] = strKey;
            }

            return strKey;
        }
    }
}

五、執行測試

新建一個控制檯程式：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using LinkTo.ORM.Model;

namespace LinkTo.ORM.Client
{
    class Program
    {
        static void Main()
        {
            //新增
            Person insertPerson = new Person
            {
                Name = "Hello",Age = 18,Gender = "male"
            };
            int insertResult = DBHelper.Insert(insertPerson);
            Console.WriteLine($"共新增了 {insertResult} 條記錄。");

            //更新
            List<Person> updateList = DBHelper.Query<Person>("Name=‘Hello‘");
            int updateResult = 0;
            if (updateList.Count > 0)
            {
                foreach (var item in updateList)
                {
                    Person updatePerson = item;
                    updatePerson.Age = 19;
                    updateResult += DBHelper.Update(updatePerson);
                }
            }
            Console.WriteLine($"共更新了 {updateResult} 條記錄。");

            //查詢
            List<Person> selectList = DBHelper.Query<Person>("Name=‘Hello‘");
            if (selectList.Count > 0)
            {
                foreach (var item in selectList)
                {
                    Console.WriteLine("person.Name = " + item.Name);
                    Console.WriteLine("person.Age = " + item.Age);
                    Console.WriteLine("person.Gender = " + item.Gender);
                }
            }

            //刪除
            int deleteResult = DBHelper.Delete<Person>("Name=‘Hello‘");
            Console.WriteLine($"共刪除了 {deleteResult} 條記錄。");

            Console.Read();
        }
    }
}

執行結果如下：

原始碼下載

參考自：

MiniORM

https://blog.csdn.net/m0_37224390/article/details/81134550