Question

以下是我的代码，我将数据表转换为类列表

       var cities = ds.Tables[0].AsEnumerable().Select(c => new City
                {
                    CityCode = c.Field<object>("CITY_CODE"),
                    CityMid = c.Field<object>("CITY_MID"),
                    CityName = c.Field<object>("CITY_NAME"),
                    CountryCode = c.Field<object>("COUNTRY_CODE"),
                    StateCode = c.Field<object>("STATE_CODE"),
                    ActiveFlag = c.Field<object>("ACTIVE_FLG"),

                }).ToList();

我的问题是如何使.Select（）参数动态化

即

c => new City     {
                    CityCode = c.Field<object>("CITY_CODE"),
                    CityMid = c.Field<object>("CITY_MID"),
                    CityName = c.Field<object>("CITY_NAME"),
                    CountryCode = c.Field<object>("COUNTRY_CODE"),
                    StateCode = c.Field<object>("STATE_CODE"),
                    ActiveFlag = c.Field<object>("ACTIVE_FLG"),

                }

我知道我必须返回表达式，但是我不明白该如何使用任何类？

Answer 1

数据类型为Func<DataRow, City>，该函数采用DataRow并返回City：

public IEnumerable<City> GetCities(Func<DataRow, City> selector)
{
    return ds.Tables[0].AsEnumerable().Select(selector).ToList();
}

像

那样称呼它

var cities = GetCities(c => new City     
{
    CityCode = c.Field<object>("CITY_CODE"),
    CityMid = c.Field<object>("CITY_MID"),
    CityName = c.Field<object>("CITY_NAME"),
    CountryCode = c.Field<object>("COUNTRY_CODE"),
    StateCode = c.Field<object>("STATE_CODE"),
    ActiveFlag = c.Field<object>("ACTIVE_FLG"),
});

或使用上述类型的另一个变量：

Func<DataRow, City> myfunc = c => new City     
{
    CityCode = c.Field<object>("CITY_CODE"),
    CityMid = c.Field<object>("CITY_MID"),
    CityName = c.Field<object>("CITY_NAME"),
    CountryCode = c.Field<object>("COUNTRY_CODE"),
    StateCode = c.Field<object>("STATE_CODE"),
    ActiveFlag = c.Field<object>("ACTIVE_FLG"),
};

var cities = GetCities(myfunc);

如果您的课程不仅是City，而且是不同的课程，则可以使用泛型：

public IEnumerable<T> GetCities(Func<DataRow, T> selector)
{
    return ds.Tables[0].AsEnumerable().Select(selector).ToList();
}

Answer 2

我知道我必须返回表达式，但是我不明白该如何使用任何类？

c => new City { ... }是类型delegate的{{1}}，在某种程度上等效于获取Func<DataRow, City>并返回DataRow的Method。因此，您可以为其创建方法。

City

，然后将该方法传递给City ConvertToCity(DataRow row) => new City { CityCode = row.Field<object>("CITY_CODE"), CityMid = row.Field<object>("CITY_MID"), CityName = row.Field<object>("CITY_NAME"), CountryCode = row.Field<object>("COUNTRY_CODE"), StateCode = row.Field<object>("STATE_CODE"), ActiveFlag = row.Field<object>("ACTIVE_FLG"), };函数：

Select

使用任何类动态创建Func <t，tr> C＃

2 个答案: