public static List<T> ToList<T>(DataTable dt)
{
List<T> list = new List<T>();
if (dt == null) return list;
DataTableEntityBuilder<T> eblist = DataTableEntityBuilder<T>.CreateBuilder(dt.Rows[0]);
foreach (DataRow info in dt.Rows)
list.Add(eblist.Build(info));
dt.Dispose();
dt = null;
return list;
}
public class DataTableEntityBuilder<T>
{
private static readonly MethodInfo getValueMethod =
typeof(DataRow).GetMethod("get_Item", new Type[] { typeof(int) });
private static readonly MethodInfo isDBNullMethod =
typeof(DataRow).GetMethod("IsNull", new Type[] { typeof(int) });
private delegate T Load(DataRow dataRecord);
private Load handler;
private DataTableEntityBuilder() { }
public T Build(DataRow dataRecord)
{
return handler(dataRecord);
}
public static DataTableEntityBuilder<T> CreateBuilder(DataRow dataRow)
{
DataTableEntityBuilder<T> dynamicBuilder = new DataTableEntityBuilder<T>();
DynamicMethod method = new DynamicMethod("DynamicCreateEntity",
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 < dataRow.ItemArray.Length; index++)
{
PropertyInfo propertyInfo = typeof(T).GetProperty(dataRow.Table.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);
dynamicBuilder.handler = (Load)method.CreateDelegate(typeof(Load));
return dynamicBuilder;
}
}
using System;
using System.Collections.Generic;
using System.Text;
using System.Data;
using System.Reflection;
using System.Reflection.Emit;
using System.Web.Caching;
using System.Web;
namespace LinFramework
{
/// <summary>
/// 实体转换
/// </summary>
public class EntityConverter
{
//数据类型和对应的强制转换方法的methodinfo，供实体属性赋值时调用
private static Dictionary<Type, MethodInfo> ConvertMethods = new Dictionary<Type, MethodInfo>()
{
{typeof(int),typeof(Convert).GetMethod("ToInt32",new Type[]{typeof(object)})},
{typeof(Int16),typeof(Convert).GetMethod("ToInt16",new Type[]{typeof(object)})},
{typeof(Int64),typeof(Convert).GetMethod("ToInt64",new Type[]{typeof(object)})},
{typeof(DateTime),typeof(Convert).GetMethod("ToDateTime",new Type[]{typeof(object)})},
{typeof(decimal),typeof(Convert).GetMethod("ToDecimal",new Type[]{typeof(object)})},
{typeof(Double),typeof(Convert).GetMethod("ToDouble",new Type[]{typeof(object)})},
{typeof(Boolean),typeof(Convert).GetMethod("ToBoolean",new Type[]{typeof(object)})},
{typeof(string),typeof(Convert).GetMethod("ToString",new Type[]{typeof(object)})}
};
//把datarow转换为实体的方法的委托定义
public delegate T LoadDataRow<T>(DataRow dr);
//把datareader转换为实体的方法的委托定义
public delegate T LoadDataRecord<T>(IDataRecord dr);
//emit里面用到的针对datarow的元数据信息
private static readonly AssembleInfo dataRowAssembly = new AssembleInfo(typeof(DataRow));
//emit里面用到的针对datareader的元数据信息
private static readonly AssembleInfo dataRecordAssembly = new AssembleInfo(typeof(IDataRecord));
/// <summary>
/// 构造转换动态方法（核心代码），根据assembly可处理datarow和datareader两种转换
/// </summary>
/// <typeparam name="T">返回的实体类型</typeparam>
/// <param name="assembly">待转换数据的元数据信息</param>
/// <returns>实体对象</returns>
private static DynamicMethod BuildMethod<T>(AssembleInfo assembly)
{
DynamicMethod method = new DynamicMethod(assembly.MethodName + typeof(T).Name, MethodAttributes.Public | MethodAttributes.Static, CallingConventions.Standard, typeof(T),
new Type[] { assembly.SourceType }, typeof(EntityContext).Module, 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);
foreach (PropertyInfo property in typeof(T).GetProperties())
{
Label endIfLabel = generator.DefineLabel();
generator.Emit(OpCodes.Ldarg_0);
generator.Emit(OpCodes.Ldstr, property.Name);
generator.Emit(OpCodes.Callvirt, assembly.CanSettedMethod);
generator.Emit(OpCodes.Brfalse, endIfLabel);
generator.Emit(OpCodes.Ldloc, result);
generator.Emit(OpCodes.Ldarg_0);
generator.Emit(OpCodes.Ldstr, property.Name);
generator.Emit(OpCodes.Callvirt, assembly.GetValueMethod);
if (property.PropertyType.IsValueType || property.PropertyType == typeof(string))
generator.Emit(OpCodes.Call, ConvertMethods[property.PropertyType]);
else
generator.Emit(OpCodes.Castclass, property.PropertyType);
generator.Emit(OpCodes.Callvirt, property.GetSetMethod());
generator.MarkLabel(endIfLabel);
}
generator.Emit(OpCodes.Ldloc, result);
generator.Emit(OpCodes.Ret);
return method;
}
/// <summary>
/// 从Cache获取委托 LoadDataRow<T>的方法实例，没有则调用BuildMethod构造一个。
/// </summary>
/// <typeparam name="T"></typeparam>
/// <returns></returns>
private static LoadDataRow<T> GetDataRowMethod<T>()
{
string key = dataRowAssembly.MethodName + typeof(T).Name;
LoadDataRow<T> load = null;
if (HttpRuntime.Cache[key] == null)
{
load = (LoadDataRow<T>)BuildMethod<T>(dataRowAssembly).CreateDelegate(typeof(LoadDataRow<T>));
HttpRuntime.Cache[key] = load;
}
else
{
load = HttpRuntime.Cache[key] as LoadDataRow<T>;
}
return load;
}
/// <summary>
/// 从Cache获取委托 LoadDataRecord<T>的方法实例，没有则调用BuildMethod构造一个。
/// </summary>
/// <typeparam name="T"></typeparam>
/// <returns></returns>
private static LoadDataRecord<T> GetDataRecordMethod<T>()
{
string key = dataRecordAssembly.MethodName + typeof(T).Name;
LoadDataRecord<T> load = null;
if (HttpRuntime.Cache[key] == null)
{
load = (LoadDataRecord<T>)BuildMethod<T>(dataRecordAssembly).CreateDelegate(typeof(LoadDataRecord<T>));
HttpRuntime.Cache[key] = load;
}
else
{
load = HttpRuntime.Cache[key] as LoadDataRecord<T>;
}
return load;
}
public static T ToItem<T>(DataRow dr)
{
LoadDataRow<T> load = GetDataRowMethod<T>();
return load(dr);
}
public static List<T> ToList<T>(DataTable dt)
{
List<T> list = new List<T>();
if (dt == null || dt.Rows.Count == 0)
{
return list;
}
LoadDataRow<T> load = GetDataRowMethod<T>();
foreach (DataRow dr in dt.Rows)
{
list.Add(load(dr));
}
return list;
}
public static List<T> ToList<T>(IDataReader dr)
{
List<T> list = new List<T>();
LoadDataRecord<T> load = GetDataRecordMethod<T>();
while (dr.Read())
{
list.Add(load(dr));
}
return list;
}
}
/// <summary>
/// emit所需要的元数据信息
/// </summary>
public class AssembleInfo
{
public AssembleInfo(Type type)
{
SourceType = type;
MethodName = "Convert" + type.Name + "To";
CanSettedMethod = this.GetType().GetMethod("CanSetted", new Type[] { type, typeof(string) });
GetValueMethod = type.GetMethod("get_Item", new Type[] { typeof(string) });
}
public string MethodName;
public Type SourceType;
public MethodInfo CanSettedMethod;
public MethodInfo GetValueMethod;
/// <summary>
/// 判断datareader是否存在某字段并且值不为空
/// </summary>
/// <param name="dr">当前的datareader</param>
/// <param name="name">字段名</param>
/// <returns></returns>
public static bool CanSetted(IDataRecord dr, string name)
{
bool result = false;
for (int i = 0; i < dr.FieldCount; i++)
{
if (dr.GetName(i).Equals(name, StringComparison.CurrentCultureIgnoreCase) && !dr[i].Equals(DBNull.Value))
{
result = true;
break;
}
}
return result;
}
/// <summary>
/// 判断datarow所在的datatable是否存在某列并且值不为空
/// </summary>
/// <param name="dr">当前datarow</param>
/// <param name="name">字段名</param>
/// <returns></returns>
public static bool CanSetted(DataRow dr, string name)
{
return dr.Table.Columns.Contains(name) && !dr.IsNull(name);
}
}
}
四、如何使用
使用起来就很简单了
List<E> list = EntityConverter.ToList<E>(dr);
...
List<E> list = EntityConverter.ToList<E>(dt);
当然，利用泛型还可以再进一步封装，
public List<TEntity> QueryBySQL<TEntity>(string sql)
{
using (IDataReader dr = sqlCommand.ExecuteReader(sql)
{
return EntityConverter.ToList<TEntity>(dr);
}
}