DataTable和List之间互转

参考https://www.cnblogs.com/shiyh/p/7478241.html

Table to List 

一、

static public List<T> Tolist<T>(DataTable dt) where T : class, new()
        {
            Type t = typeof(T);
            PropertyInfo[] PropertyInfo = t.GetProperties();
            List<T> list = new List<T>();

            string typeName = string.Empty;
            foreach (DataRow item in dt.Rows)
            {
                T obj = new T();
                foreach (PropertyInfo s in PropertyInfo)
                {
                    typeName = s.Name;
                    if (dt.Columns.Contains(typeName))
                    {
                        if (!s.CanWrite) continue;

                        object value = item[typeName];
                        if (value == DBNull.Value) continue;

                        if (s.PropertyType == typeof(string))
                        {
                            s.SetValue(obj, value.ToString(), null);
                        }
                        else
                        {
                            s.SetValue(obj, value, null);
                        }
                    }
                }
                list.Add(obj);
            }
            return list;
        }

二、

public static IList<T> ConvertTo<T>(DataTable table)  
{  
   if (table == null)  
   {  
       return null;  
   }  
 
   List<DataRow> rows = new List<DataRow>();  
 
   foreach (DataRow row in table.Rows)  
   {  
       rows.Add(row);  
   }  
 
   return ConvertTo<T>(rows);  
}  
 
public static IList<T> ConvertTo<T>(IList<DataRow> rows)  
{  
   IList<T> list = null;  
 
   if (rows != null)  
   {  
       list = new List<T>();  
 
       foreach (DataRow row in rows)  
       {  
           T item = CreateItem<T>(row);  
           list.Add(item);  
       }  
   }  
 
   return list;
}    
 
public static T CreateItem<T>(DataRow row)    
{
    T obj = default(T);    
    if (row != null)    
    {    
       obj = Activator.CreateInstance<T>();    
 
       foreach (DataColumn column in row.Table.Columns)    
       {    
           PropertyInfo prop = obj.GetType().GetProperty(column.ColumnName);    
           try   
           {    
               object value = row[column.ColumnName];    
               prop.SetValue(obj, value, null);    
           }    
           catch   
           {  //You can log something here     
               //throw;    
           }    
       }    
    }    
 
return obj;    
}

三、利用反射和泛型，创建实体转换辅助类

调用;  IList<UserInfo> users = ModelConvertHelper<UserInfo>.ConvertToModel(dt);

using System;      
using System.Collections.Generic;  
using System.Text;    
using System.Data;    
using System.Reflection;  
namespace NCL.Data    
{    
    /// <summary>    
    /// 实体转换辅助类    
    /// </summary>    
    public class ModelConvertHelper<T> where   T : new()    
     {    
        public static IList<T> ConvertToModel(DataTable dt)    
         {    
            // 定义集合    
             IList<T> ts = new List<T>(); 
     
            // 获得此模型的类型   
             Type type = typeof(T);      
            string tempName = "";      
      
            foreach (DataRow dr in dt.Rows)      
             {    
                 T t = new T();     
                // 获得此模型的公共属性      
                 PropertyInfo[] propertys = t.GetType().GetProperties(); 
                foreach (PropertyInfo pi in propertys)      
                 {      
                     tempName = pi.Name;  // 检查DataTable是否包含此列    
   
                    if (dt.Columns.Contains(tempName))      
                     {      
                        // 判断此属性是否有Setter      
                        if (!pi.CanWrite) continue;         
   
                        object value = dr[tempName];      
                        if (value != DBNull.Value)      
                             pi.SetValue(t, value, null);  
                     }     
                 }      
                 ts.Add(t);      
             }     
            return ts;     
         }     
     }    
}

三(1):

        /// <summary>
        /// DateTable转为List
        /// </summary>
        /// <returns></returns>
        public static List<T> ToList<T>(this DataTable dt)
        {
            List<string> dataColumn = dt.Columns.Cast<DataColumn>().Select(c => c.ColumnName).ToList();
            PropertyInfo[] properties = typeof(T).GetProperties();
            string columnName = string.Empty;
            return dt.AsEnumerable().Select(row =>
            {
                T t = Activator.CreateInstance<T>();
                foreach (PropertyInfo p in properties)
                {
                    columnName = p.Name;
                    if (dataColumn.Contains(columnName))
                    {
                        if (!p.CanWrite)
                            continue;
                        object value = row[columnName];
                        Type type = p.PropertyType;
                        if (value != DBNull.Value)
                            p.SetValue(t, Convert.ChangeType(value, type), null);
                    }
                }
                return t;
            }).ToList();
        }

四、高性能的基于Emit的实现

/// <summary>
/// 把datatable转换为对象集合列表List<T>
/// </summary>
    public class DataTableConvert
    {
        //把DataRow转换为对象的委托声明
        private delegate T Load<T>(DataRow dataRecord);

        //用于构造Emit的DataRow中获取字段的方法信息
        private static readonly MethodInfo getValueMethod = typeof(DataRow).GetMethod("get_Item", new Type[] { typeof(int) });

        //用于构造Emit的DataRow中判断是否为空行的方法信息
        private static readonly MethodInfo isDBNullMethod = typeof(DataRow).GetMethod("IsNull", new Type[] { typeof(int) });

        //使用字典存储实体的类型以及与之对应的Emit生成的转换方法
        private static Dictionary<Type, Delegate> rowMapMethods = new Dictionary<Type, Delegate>();

        public static List<T> ToList<T>(DataTable dt)
        {
            List<T> list = new List<T>();
            if (dt == null)
                return list;

            //声明 委托Load<T>的一个实例rowMap
            Load<T> rowMap = null;


            //从rowMapMethods查找当前T类对应的转换方法，没有则使用Emit构造一个。
            if (!rowMapMethods.ContainsKey(typeof(T)))
            {
                DynamicMethod method = new DynamicMethod("DynamicCreateEntity_" + typeof(T).Name, typeof(T), new Type[] { typeof(DataRow) }, typeof(T), true);
                ILGenerator generator = method.GetILGenerator();
                LocalBuilder result = generator.DeclareLocal(typeof(T));
                generator.Emit(OpCodes.Newobj, typeof(T).GetConstructor(Type.EmptyTypes));
                generator.Emit(OpCodes.Stloc, result);

                for (int index = 0; index < dt.Columns.Count; index++)
                {
                    PropertyInfo propertyInfo = typeof(T).GetProperty(dt.Columns[index].ColumnName);
                    Label endIfLabel = generator.DefineLabel();
                    if (propertyInfo != null && propertyInfo.GetSetMethod() != null)
                    {
                        generator.Emit(OpCodes.Ldarg_0);
                        generator.Emit(OpCodes.Ldc_I4, index);
                        generator.Emit(OpCodes.Callvirt, isDBNullMethod);
                        generator.Emit(OpCodes.Brtrue, endIfLabel);
                        generator.Emit(OpCodes.Ldloc, result);
                        generator.Emit(OpCodes.Ldarg_0);
                        generator.Emit(OpCodes.Ldc_I4, index);
                        generator.Emit(OpCodes.Callvirt, getValueMethod);
                        generator.Emit(OpCodes.Unbox_Any, propertyInfo.PropertyType);
                        generator.Emit(OpCodes.Callvirt, propertyInfo.GetSetMethod());
                        generator.MarkLabel(endIfLabel);
                    }
                }
                generator.Emit(OpCodes.Ldloc, result);
                generator.Emit(OpCodes.Ret);

                //构造完成以后传给rowMap
                rowMap = (Load<T>)method.CreateDelegate(typeof(Load<T>));
            }
            else
            {
                rowMap = (Load<T>)rowMapMethods[typeof(T)];
            }

            //遍历Datatable的rows集合，调用rowMap把DataRow转换为对象（T）
            foreach (DataRow info in dt.Rows)
                list.Add(rowMap(info));
            return list;

        }
    }

List To Tabel

一、

/// <summary>
/// Convert a List{T} to a DataTable.
/// </summary>
private DataTable ToDataTable<T>(List<T> items)
{
    var tb = new DataTable(typeof (T).Name);
 
    PropertyInfo[] props = typeof (T).GetProperties(BindingFlags.Public | BindingFlags.Instance);
 
    foreach (PropertyInfo prop in props)
    {
        Type t = GetCoreType(prop.PropertyType);
        tb.Columns.Add(prop.Name, t);
    }
 
    foreach (T item in items)
    {
        var values = new object[props.Length];
 
        for (int i = 0; i < props.Length; i++)
        {
            values[i] = props[i].GetValue(item, null);
        }
 
        tb.Rows.Add(values);
    }
 
    return tb;
}
 
/// <summary>
/// Determine of specified type is nullable
/// </summary>
public static bool IsNullable(Type t)
{
    return !t.IsValueType || (t.IsGenericType && t.GetGenericTypeDefinition() == typeof(Nullable<>));
}
 
/// <summary>
/// Return underlying type if type is Nullable otherwise return the type
/// </summary>
public static Type GetCoreType(Type t)
{
    if (t != null && IsNullable(t))
    {
        if (!t.IsValueType)
        {
            return t;
        }
        else
        {
            return Nullable.GetUnderlyingType(t);
        }
    }
    else
    {
        return t;
    }
}

二、

public static DataTable ToDataTable<T>(IEnumerable<T> collection)
 {
     var props = typeof(T).GetProperties();
     var dt = new DataTable();
     dt.Columns.AddRange(props.Select(p => new DataColumn(p.Name, p.PropertyType)).ToArray());
     if (collection.Count() > 0)
     {
         for (int i = 0; i < collection.Count(); i++)
         {
             ArrayList tempList = new ArrayList();
             foreach (PropertyInfo pi in props)
             {
                 object obj = pi.GetValue(collection.ElementAt(i), null);
                 tempList.Add(obj);
             }
             object[] array = tempList.ToArray();
             dt.LoadDataRow(array, true);
         }
     }
     return dt;
 }

高性能的基于Emit实现的