用DataRow参数递归调用泛型函数——MakeGenericMethod失败

本文关键字：函数 MakeGenericMethod 失败 泛型 调用 DataRow 参数 递归 | 更新日期: 2023-09-27 18:02:26

问题是:如果我有MyConvertDataRowToEntity(DataRow row)和我调用T对象从类型Parent和内部我调用相同的函数与子类型Child我该如何传递DataRow参数?这个问题是在调用MakeGenericMethod的Invoke时产生的。将类型更改为DataSet, string和string类型。没有运气。(我在列名中识别子对象但前缀- prefixdataccolumn) 

public static T MyConvertDataRowToEntity<T>(DataRow row ) where T : class, new()
    {
        Type objType = typeof(T);
        Type parentObjType = typeof(T);
        T obj = Activator.CreateInstance<T>(); //hence the new() contsraint
        PropertyInfo propertyGenericType = null;
        object childInstance = null;
        PropertyInfo property;
        string childColumnName = string.Empty ;
        foreach (DataColumn column in row.Table.Columns)
        {
            column.ColumnName = column.ColumnName.Replace("_", "");
            string PrefixDataColumn;
            if (column.ColumnName.IndexOf(".") > (-1))
            {
                ///gets the prefix that is the same as child entity name
                PrefixDataColumn = column.ColumnName.Substring(0, column.ColumnName.IndexOf("."));
                ///the column name in the child
                int length = column.ColumnName.Length - 1;
                int start = column.ColumnName.IndexOf(".") + 1;
                childColumnName = column.ColumnName.Substring(column.ColumnName.IndexOf(".") + 1);
                propertyGenericType = objType.GetProperty(PrefixDataColumn,
                                    BindingFlags.Public | BindingFlags.Instance | BindingFlags.IgnoreCase | BindingFlags.FlattenHierarchy);
                parentObjType = objType;
                if (propertyGenericType != null)
                {
                    Type childType = propertyGenericType.PropertyType;
                    objType = childType;
                    childInstance = Activator.CreateInstance(propertyGenericType.PropertyType);

                    // get the get method for the property
                    MethodInfo method = propertyGenericType.GetGetMethod(true);
                    // get the generic get-method generator 
                    MethodInfo genericHelper = typeof(DataUtil).GetMethod("MyConvertDataRowToEntity", BindingFlags.Public | BindingFlags.Static);
                    List<Type> signature = new List<Type>();
                    // first type parameter is type of target object
                    signature.Add(childType);
                    //next parameters are real types of method arguments
                    foreach (ParameterInfo pi in genericHelper.GetParameters())
                    {
                        signature.Add(pi.ParameterType);
                    }
                    // last parameters are known types of method arguments
                    signature.AddRange(typeof(T).GetGenericArguments());
                    // reflection call to the generic get-method generator to generate the type arguments
                    //MethodInfo constructedHelper = genericHelper.MakeGenericMethod(signature.ToArray());
                    // reflection call to the generic get-method generator to generate the type arguments
                    MethodInfo constructedHelper = genericHelper.MakeGenericMethod(childType );
                    // now call it. The null argument is because it's a static method.
                    object ret = constructedHelper.Invoke(null, new object[] { method });
                   // object myObj =  method.Invoke(null, row);
                   //// property.SetValue(obj, MyConvertDataRowToEntity<childInstance>(DataRow row),null);
                   // childInstance = DataUtil.GetMethod("MyConvertDataRowToEntity").MakeGenericMethod(childType); //MyConvertDataRowToEntity<object>(row); 
                    //childType initializedChild = ;
                    //property.SetValue(obj, value, null);
                    //objType = parentObjType;
                }
                else
                {
                    continue; 
                }
            }

        }
        return obj;
    }

得到这个错误:System.Reflection类型的对象。RuntimeMethodInfo'不能转换为'System.Data.DataRow'类型。

有解决办法吗?

注。尽可能缩小代码范围。

如何使用继承类型递归地调用方法并传递数据流?

用DataRow参数递归调用泛型函数——MakeGenericMethod失败

错误的原因是因为您正在调用MyConvertDataRowToEntity<ChildType>，但随后将属性的getaccessor方法作为参数传递，而不是仅包含这些字段的数据行。

如果您想继续使用当前使用的代码处理逻辑，则需要构造一个新的数据流，其中包含从列名开头删除的所需字段(带有前缀和"。")。

或者，您可以创建一个助手方法，接受一个列名，源对象，它只是更新值。

static void UpdateItemProperty<T>(T item, string columnName, object rowValue) {
  var prefixColumn=columnName.IndexOf(".")==-1 ? columnName : columnName.Split(".")[0];
  var pi = typeof(T).GetProperty(prefixColumn // Add your binding flags);
  // if pi==null then there is an error...
  if (column.ColumnName.IndexOf(".") == (-1)) { // No Nesting
    pi.SetValue(item,rowValue);
    return;
  }
  // Nesting 
  var child=pi.GetValue(item);
  if (child==null) {
        // Logic here to get childs type and create an instance then call pi.SetValue with child
  }
  var remainder=string.Join(',',columnName.Split(".").Skip(1).ToArray());
  // make your generic method info for UpdateItemProperty with pi.PropertyType into mi
  mi.Invoke(null,new object[] { child,remainder,value };
}
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