通过反射 c# 生成嵌套类的实例

Question

我有一个 DAL，它可以访问多个 CSV 文件，这些文件不断更新其格式，并不断添加新格式。

CSV 文件中的每一行都代表系统中的一个 class，但由于格式众多，输入通过两步处理。

步骤 1. 将 CSV 文件中的行转换为值列表。将此值列表转换为 "raw" 对象。

此原始对象稍后将映射到业务逻辑对象，因此所有原始对象都将转换为业务逻辑对象。

但是，由于某些 csv 行严重倾向于使用嵌套 class 生成 class，我的通用映射器目前用处不大。

映射对象，是一个属性，其索引位置由属性上的属性分配的值字段。

public static T BuildRawObject(string[] values)
        {
            T target = (T) Activator.CreateInstance(typeof(T), new object[] { });

            Type targetInfo = target.GetType();
            foreach (PropertyInfo pi in targetInfo.GetProperties())
            {
                if (!pi.PropertyType.IsValueType)
                {


                    if (pi.PropertyType.IsAssignableFrom(typeof(NestedObj1)))
                    {
                        var result = BuildRawObject2<NestedObj1>(values);
                        try
                        {
                            pi.SetValue(target, Convert.ChangeType(result, pi.PropertyType));
                        }
                        catch (Exception e)
                        {
                            Console.WriteLine("Exception on property: " + pi.PropertyType +
                                              " was bit not to set built instance on property. Instace was: " + result);
                            Console.WriteLine("Exception mesessage was: " + e.Message);
                            if (e.InnerException != null)
                            {
                                Console.WriteLine("Inner Exception message was: " + e.InnerException.Message);
                            }
                        }
                    }
                    else if(pi.PropertyType.IsAssignableFrom(typeof(NestedObj2)))
                    {
                        var result = BuildRawObject2<NestedObj2>(values);
                        try
                        {
                            pi.SetValue(target, Convert.ChangeType(result, pi.PropertyType));
                        }
                        catch (Exception e)
                        {
                            Console.WriteLine("Exception on property: " + pi.PropertyType +
                                              " was bit not to set built instance on property. Instace was: " + result);
                            Console.WriteLine("Exception mesessage was: " + e.Message);
                            if (e.InnerException != null)
                            {
                                Console.WriteLine("Inner Exception message was: " + e.InnerException.Message);
                            }
                        }
                    }
                    else if (pi.PropertyType.IsAssignableFrom(typeof(NestedObj3)))
                    {
                        var result = BuildRawObject2<NestedObj3>(values);
                        try
                        {
                            pi.SetValue(target, Convert.ChangeType(result, pi.PropertyType));
                        }
                        catch (Exception e)
                        {
                            Console.WriteLine("Exception on property: " + pi.PropertyType +
                                              " was bit not to set built instance on property. Instace was: " + result);
                            Console.WriteLine("Exception mesessage was: " + e.Message);
                            if (e.InnerException != null)
                            {
                                Console.WriteLine("Inner Exception message was: " + e.InnerException.Message);
                            }
                        }
                    }
                    else if (pi.PropertyType.IsAssignableFrom(typeof(NestedObj5)))
                    {
                        var result = BuildRawObject2<NestedObj5>(values);
                        try
                        {
                            pi.SetValue(target, Convert.ChangeType(result, pi.PropertyType));
                        }
                        catch (Exception e)
                        {
                            Console.WriteLine("Exception on property: " + pi.PropertyType +
                                              " was bit not to set built instance on property. Instace was: " + result);
                            Console.WriteLine("Exception mesessage was: " + e.Message);
                            if (e.InnerException != null)
                            {
                                Console.WriteLine("Inner Exception message was: " + e.InnerException.Message);
                            }
                        }
                    }
                    else if (pi.PropertyType.IsAssignableFrom(typeof(NestedObj6)))
                    {
                        var result = BuildRawObject2<NestedObj6>(values);
                        try
                        {
                            pi.SetValue(target, result);
                        }
                        catch (Exception e)
                        {
                            Console.WriteLine("Exception on property: " + pi.PropertyType +
                                              " was bit not to set built instance on property. Instace was: " + result);
                            Console.WriteLine("Exception mesessage was: " + e.Message);
                            if (e.InnerException != null)
                            {
                                Console.WriteLine("Inner Exception message was: " + e.InnerException.Message);
                            }
                        }
                    }
                    else if (pi.PropertyType.IsAssignableFrom(typeof(NestedObj7)))
                    {
                        var result = BuildRawObject2<NestedObj7>(values);
                        try
                        {
                            pi.SetValue(target, Convert.ChangeType(result, pi.PropertyType));
                        }
                        catch (Exception e)
                        {
                            Console.WriteLine("Exception on property: " + pi.PropertyType +
                                              " was bit not to set built instance on property. Instace was: " + result);
                            Console.WriteLine("Exception mesessage was: " + e.Message);
                            if (e.InnerException != null)
                            {
                                Console.WriteLine("Inner Exception message was: " + e.InnerException.Message);
                            }
                        }
                    }
                    else
                    {
                       Console.WriteLine("An unrecognized class exists in the raw object. This will not be mapped to: " + pi.Name);
                    }

                }
                else
                {
                    Mapping mapping = pi.GetCustomAttribute<Mapping>();
                    if (mapping != null)
                    {
                        values[mapping.SourceIndex] = EmptyStringValuesWhenEmpty(values[mapping.SourceIndex]);
                        if (pi.PropertyType == typeof(DateTime) || pi.PropertyType == typeof(DateTime?))
                        {
                            bool valid = DateTime.TryParse(values[mapping.SourceIndex], out DateTime dateTime);
                            if (valid)
                            {
                                pi.SetValue(target, dateTime, null);
                            }
                            else
                            {
                                Console.WriteLine("Value: " + values[mapping.SourceIndex] + " on position[" +
                                                  mapping.SourceIndex + "] was not a valid date time. Value is required.");
                            }
                        }
                        else
                        {
                            try
                            {
                                pi.SetValue(target, GenericConverter(values[mapping.SourceIndex], pi.PropertyType), null);
                            }
                            catch (Exception e)
                            {
                                Console.WriteLine("Exception on index: " + mapping.SourceIndex + " contained value: " +
                                                  values[mapping.SourceIndex] + " was attempted for property type: " +
                                                  pi.PropertyType +
                                                  "Parse was not possible. Either input file is in wrong format, or RawInputObject has incorect property");
                                Console.WriteLine("Exception mesessage was: " + e.Message);
                                if (e.InnerException != null)
                                {
                                    Console.WriteLine("Inner Exception message was: " + e.InnerException.Message);
                                }
                            }
                        }
                    }
                    else
                    {
                        Console.WriteLine("Mapping to field: " + pi.Name +
                                          " was skipped due to missing mapping attribute definition.");
                    }
                }
            }
            return target;
        }

当我尝试为 "Raw return object".

的嵌套 classes 赋值时，问题就来了

理想情况下，我更愿意将整个事情变成一个递归方法。但是，父 class 与嵌套 class 的类型不同。所以我必须生成一个新方法，它与父 class 相同，但接受嵌套的 classes

但是，从理论上讲，生成可能出现在泛型方法中的命名类型对象的无限列表是……错误的。我宁愿简单地让程序从传递给方法的任何专门的嵌套 class 进行推断，以确定方法的 return 类型。这可能吗？我不知道怎么办。

如果我的问题不清楚，或者您对我如何更好地提出问题有建议，请告诉我。如果缺少细节。请指教，我会提供。

编辑：提供解决方案后的方法

public static object BuildRawObject(Type objectType, string[] values)
    {
        dynamic target = Activator.CreateInstance(objectType, new object[] { });

        Type targetInfo = target.GetType();
        foreach (PropertyInfo pi in targetInfo.GetProperties())
        {
            if (pi.PropertyType.GetInterfaces().AsEnumerable().Contains(typeof(IRawObjectBase))  || pi.PropertyType.GetInterfaces().AsEnumerable().Contains(typeof(IRawNestedObjectBase)))
            {
                var result = BuildRawObject(pi.PropertyType, values);
                try
                {
                    pi.SetValue(target, Convert.ChangeType(result, pi.PropertyType));
                }
                catch (Exception e)
                {
                    Console.WriteLine("Exception on property: " + pi.PropertyType +
                                      " was bit not to set built instance on property. Instace was: " + result);
                    Console.WriteLine("Exception mesessage was: " + e.Message);
                    if (e.InnerException != null)
                    {
                        Console.WriteLine("Inner Exception message was: " + e.InnerException.Message);
                    }
                }

            }
            else
            {
                Mapping mapping = pi.GetCustomAttribute<Mapping>();
                if (mapping != null)
                {
                    values[mapping.SourceIndex] = EmptyStringValuesWhenEmpty(values[mapping.SourceIndex]);
                    if (pi.PropertyType == typeof(DateTime) || pi.PropertyType == typeof(DateTime?))
                    {
                        bool valid = DateTime.TryParse(values[mapping.SourceIndex], out DateTime dateTime);
                        if (valid)
                        {
                            pi.SetValue(target, dateTime, null);
                        }
                        else
                        {
                            Console.WriteLine("Value: " + values[mapping.SourceIndex] + " on position[" +
                                              mapping.SourceIndex + "] was not a valid date time. Value is required.");
                        }
                    }
                    else
                    {
                        try
                        {
                            pi.SetValue(target, GenericConverter(values[mapping.SourceIndex], pi.PropertyType), null);
                        }
                        catch (Exception e)
                        {
                            Console.WriteLine("Exception on index: " + mapping.SourceIndex + " contained value: " +
                                              values[mapping.SourceIndex] + " was attempted for property type: " +
                                              pi.PropertyType +
                                              "Parse was not possible. Either input file is in wrong format, or RawInputObject has incorect property");
                            Console.WriteLine("Exception mesessage was: " + e.Message);
                            if (e.InnerException != null)
                            {
                                Console.WriteLine("Inner Exception message was: " + e.InnerException.Message);
                            }
                        }
                    }
                }
                else
                {
                    Console.WriteLine("Mapping to field: " + pi.Name +
                                      " was skipped due to missing mapping attribute definition.");
                }
            }
        }
        return target;
    }

Answer 1

在这种情况下，似乎不必要地使用泛型会让您感到厌烦。如果您将签名更改为

static object BuildRawObject(Type objectType, string[] values)

您将能够直接在那里传递属性类型，而无需对属性类型进行大量检查：

if (propertyIsNotPrimitiveType) {
    var result = BuildRawObject(pi.PropertyType, values);
}

为方便起见，您仍然可以保留通用重载：

static T BuildRawObject<T>(string[] values) {
     return (T) BuildRawObject(typeof(T), values);
}

通过反射 c# 生成嵌套类的实例

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通过反射 c# 生成嵌套 类 的实例

Generating instances of nested classes via reflection c#

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通过反射 c# 生成嵌套类的实例