1   /// 
 2     /// 使用Emit动态代理收集实体信息 3     /// 
 4     /// 
     
      实体类
      5     public class TDynamicBuilder
     
       6     { 7         #region 变量区域 8         private static readonly MethodInfo getValueMethod = typeof(IDataRecord).GetMethod("get_Item", new[] { typeof(int) }); 9 10         private static readonly MethodInfo isDBNullMethod = typeof(IDataRecord).GetMethod("IsDBNull", new[] { typeof(int) });11 12         private delegate T Load(IDataRecord dataRecord);13 14         /// 
      
15         /// 代理16         /// 
17         private Load Handler;//最终执行动态方法的一个委托 参数是IDataRecord接口18         #endregion19 20         #region 构造函数21         private TDynamicBuilder() { }22         #endregion23 24         #region +Build Emit动态代理生成一个实体对象25         /// 
      
26         /// Emit动态代理生成一个实体对象27         /// 
28         /// 
      DataReader接口实现对象29         /// 
      30         public T Build(IDataRecord dataRecord)31         {32             return Handler(dataRecord);//执行CreateBuilder里创建的DynamicCreate动态方法的委托33         }34         #endregion35 36         #region + CreateBuilder 创建一个Builder器37         /// 
      
38         /// 创建一个Builder器39         /// 
40         /// 
      DataReader接口实现对象41         /// 
      42         public static TDynamicBuilder
      
        CreateBuilder(IDataRecord dataRecord)43         {44             var dynamicBuilder = new TDynamicBuilder
       
        ();45             var type = typeof(T);46             //定义一个名为DynamicCreate的动态方法，返回值typof(T)，参数typeof(IDataRecord)47             var method = new DynamicMethod("DynamicCreate", type, new[] { typeof(IDataRecord) }, typeof(T), true);48             var generator = method.GetILGenerator();//创建一个MSIL生成器，为动态方法生成代码49             var result = generator.DeclareLocal(type);//声明指定类型的局部变量 可以T t;这么理解50             //The next piece of code instantiates the requested type of object and stores it in the local variable. 可以t=new T();这么理解51             generator.Emit(OpCodes.Newobj, type.GetConstructor(Type.EmptyTypes));52             generator.Emit(OpCodes.Stloc, result);53             var propertys = type.GetProperties();54             //数据集合55             for (var i = 0; i < dataRecord.FieldCount; i++)56             {57                 //查找属性58                 var propertyInfo = propertys.FirstOrDefault(a => string.Equals(a.Name.ToLower(), dataRecord.GetName(i).ToLower()));59                 if (propertyInfo == null) continue;60                 if (!string.Equals(propertyInfo.Name, dataRecord.GetName(i), StringComparison.CurrentCultureIgnoreCase)) continue;61                 //根据列名取属性  原则上属性和列是一一对应的关系62                 var endIfLabel = generator.DefineLabel();63 64                 /*The code then loops through the fields in the data reader, finding matching properties on the type passed in. 65                  * When a match is found, the code checks to see if the value from the data reader is null.66                  */67                 generator.Emit(OpCodes.Ldarg_0);68                 generator.Emit(OpCodes.Ldc_I4, i);69                 //就知道这里要调用IsDBNull方法 如果IsDBNull==true contine70                 generator.Emit(OpCodes.Callvirt, isDBNullMethod);71                 generator.Emit(OpCodes.Brtrue, endIfLabel);72 73                 /*If the value in the data reader is not null, the code sets the value on the object.*/74                 generator.Emit(OpCodes.Ldloc, result);75                 generator.Emit(OpCodes.Ldarg_0);76                 generator.Emit(OpCodes.Ldc_I4, i);77                 generator.Emit(OpCodes.Callvirt, getValueMethod); //调用get_Item方法78                 generator.Emit(OpCodes.Unbox_Any, dataRecord.GetFieldType(i));79                 generator.Emit(OpCodes.Callvirt, propertyInfo.GetSetMethod()); //给该属性设置对应值80 81                 generator.MarkLabel(endIfLabel);82 83             }84 85             /*The last part of the code returns the value of the local variable*/86             generator.Emit(OpCodes.Ldloc, result);87             generator.Emit(OpCodes.Ret);//方法结束，返回88 89             //完成动态方法的创建，并且创建执行该动态方法的委托，赋值到全局变量handler,handler在Build方法里Invoke90             dynamicBuilder.Handler = (Load)method.CreateDelegate(typeof(Load));91             return dynamicBuilder;92         }93         #endregion94 95     }