Question

我想将Linq查询插入到数据表中，但出现以下错误 IEnumberable“ <<”匿名类型无法转换为IEnumerable。为什么我会收到此错误以及如何解决？

IEnumerable<DataRow> sql = from dr in Csvdaten.AsEnumerable()
                      join dr2 in Csvimportdaten.AsEnumerable() on dr.Field<string>("customer_id_spam") equals dr2.Field<string>("customer_id_spam")
                      select new
                      {
                          CAMPAIGN_ID = Convert.ToInt32(dr2["CAMPAIGN_ID"]),
                          MEDIUM_CODE = Convert.ToString(dr2["MEDIUM_CODE"])
                      };

            DataTable dt = sql.CopyToDataTable();

Answer 1

如果您不关心匹配特定的DataTable，而只是想即时生成它们，而又不太担心反射引起的性能损失，则可以使用这些扩展。

首先，一些帮助程序扩展使使用带有属性或字段的反射更加容易：

public static class TypeExt {
    public static List<MemberInfo> GetPropertiesOrFields(this Type t, BindingFlags bf = BindingFlags.Public | BindingFlags.Instance) =>
        t.GetMembers(bf).Where(mi => mi.MemberType == MemberTypes.Field | mi.MemberType == MemberTypes.Property).ToList();    
}

public static class MemberInfoExt {
    public static Type GetMemberType(this MemberInfo member) {
        switch (member) {
            case FieldInfo mfi:
                return mfi.FieldType;
            case PropertyInfo mpi:
                return mpi.PropertyType;
            case EventInfo mei:
                return mei.EventHandlerType;
            default:
                throw new ArgumentException("MemberInfo must be if type FieldInfo, PropertyInfo or EventInfo", nameof(member));
        }
    }

    public static object GetValue(this MemberInfo member, object srcObject) {
        switch (member) {
            case FieldInfo mfi:
                return mfi.GetValue(srcObject);
            case PropertyInfo mpi:
                return mpi.GetValue(srcObject);
            default:
                throw new ArgumentException("MemberInfo must be of type FieldInfo or PropertyInfo", nameof(member));
        }
    }
    public static T GetValue<T>(this MemberInfo member, object srcObject) => (T)member.GetValue(srcObject);
}

然后是一个IEnumerable<T>扩展名，用于将IEnumerable<anonymous>转换为DataTable：

public static class IEnumerableExt {
    public static DataTable ToDataTable<T>(this IEnumerable<T> rows) {
        var dt = new DataTable();
        if (rows.Any()) {
            var rowType = typeof(T);
            var memberInfos = rowType.GetPropertiesOrFields();
            foreach (var info in memberInfos)
                dt.Columns.Add(new DataColumn(info.Name, info.GetMemberType()));

            foreach (var r in rows)
                dt.Rows.Add(memberInfos.Select(i => i.GetValue(r)).ToArray());
        }
        return dt;
    }
}

IEnumberable <<匿名类型=“” canot =“” be =“” convert =“” to =“” ienumerable <datarow =“”> C＃

1 个答案: