public static DynamicBuilder <T> CreateBuilder(IDataRecord dataRecord)
{
DynamicBuilder <T> dynamicBuilder = new DynamicBuilder <T>();
//定义一个名为DynamicCreate的动态方法，返回值typof(T)，参数typeof(IDataRecord)
DynamicMethod method = new DynamicMethod("DynamicCreate", typeof(T), new Type[] { typeof(IDataRecord) }, typeof(T), true);
ILGenerator generator = method.GetILGenerator(); //创建一个MSIL生成器，为动态方法生成代码
LocalBuilder result = generator.DeclareLocal(typeof(T)); //声明指定类型的局部变量 可以T t;这么理解
//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
generator.Emit(OpCodes.Newobj, typeof(T).GetConstructor(Type.EmptyTypes));
generator.Emit(OpCodes.Stloc, result);
for (int i = 0; i < dataRecord.FieldCount; i++) //数据集合，熟悉的for循环 要干什么你懂的
{
PropertyInfo propertyInfo = typeof(T).GetProperty(dataRecord.GetName(i)); //根据列名取属性 原则上属性和列是一一对应的关系
Label endIfLabel = generator.DefineLabel();
if (propertyInfo != null && propertyInfo.GetSetMethod() != null)//实体存在该属性 且该属性有SetMethod方法
{
/*The code then loops through the fields in the data reader, finding matching properties on the type passed in.
* When a match is found, the code checks to see if the value from the data reader is null.
*/
generator.Emit(OpCodes.Ldarg_0);
generator.Emit(OpCodes.Ldc_I4, i);
generator.Emit(OpCodes.Callvirt, isDBNullMethod);//就知道这里要调用IsDBNull方法 如果IsDBNull==true contine
generator.Emit(OpCodes.Brtrue, endIfLabel);
/*If the value in the data reader is not null, the code sets the value on the object.*/
generator.Emit(OpCodes.Ldloc, result);
generator.Emit(OpCodes.Ldarg_0);
generator.Emit(OpCodes.Ldc_I4, i);
generator.Emit(OpCodes.Callvirt, getValueMethod); //调用get_Item方法
generator.Emit(OpCodes.Unbox_Any, dataRecord.GetFieldType(i));
generator.Emit(OpCodes.Callvirt, propertyInfo.GetSetMethod()); //给该属性设置对应值
generator.MarkLabel(endIfLabel);
}
}
/*The last part of the code returns the value of the local variable*/
generator.Emit(OpCodes.Ldloc, result);
generator.Emit(OpCodes.Ret);//方法结束，返回
//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Invoke
dynamicBuilder.handler = (Load)method.CreateDelegate(typeof(Load));
return(dynamicBuilder);
}
/// <summary>
/// 执行存储过程读取数据
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="strProcedure"></param>
/// <param name="strErrText"></param>
/// <returns></returns>
protected List <T> LoadData <T>(string strProcedure, out string strErrText)
{
List <T> models = new List <T>();
SqlDataReader dr = null;
try
{
SqlCommand command = new SqlCommand();
command.Connection = m_conn;
command.CommandTimeout = 7200;
command.CommandText = strProcedure;
command.CommandType = CommandType.StoredProcedure;
m_strInfoMessage = string.Empty;
dr = command.ExecuteReader();
DynamicBuilder <T> builder = DynamicBuilder <T> .CreateBuilder(dr);
while (dr.Read())
{
T model = default(T);
model = builder.Build(dr);
models.Add(model);
}
//用于获取存储过程RaiseError命令发出的错误消息。
//如果存储过程中执行了RaiseError命令，则调用NextResult时就会引发异常
dr.NextResult();
dr.Close();
dr.Dispose();
strErrText = string.Empty;
return(models);
}
catch (Exception e)
{
if (dr != null)
{
dr.Close();
dr.Dispose();
}
strErrText = e.Message;
return(null);
}
}
