配合ModelState使用，關於使用方法，參考微軟文件

https://docs.microsoft.com/en-us/aspnet/web-api/overview/formats-and-model-binding/model-validation-in-aspnet-web-api

自定義Data Annotations只需要繼承ValidationAttribute，並且重寫IsValid方法。

示例：

// =================================================================== 
// ModelState自定義註解
// 多個欄位分組判斷，全部不允許為空或至少有一個不為空
//====================================================================
// CreateTime：2019-04-24 
// Author：liucx
// ===================================================================
using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace OF.Component.Model
{
    /// <summary>
    ///  多個屬性欄位分組不為空判斷  傳入引數逗號間隔
    ///  <example>[GroupEmpty("p1,p2,p3",false,ErrorMessage="p1p2p3三個引數中至少有一個非空")] </example>
    /// </summary>
    public class GroupEmptyAttribute : ValidationAttribute
    {
        private readonly string _groupFields;
        private readonly bool _notNullableAll;
        /// <summary>
        ///  建構函式
        /// </summary>
        /// <param name="groupFields">屬性名，多個屬性名逗號隔開</param>
        /// <param name="notNullableAll"> true全部不允許為空。 false只要存在不為空的屬性即可</param>
        public GroupEmptyAttribute(string groupFields, bool notNullableAll)
        {
            _groupFields = groupFields;
            _notNullableAll = notNullableAll;
        }
        /// <summary>
        /// 建構函式,預設至少1個非空
        /// </summary>
        /// <param name="groupFields">屬性名，多個屬性名逗號隔開</param>
        public GroupEmptyAttribute(string groupFields)
        {
            _groupFields = groupFields;
            _notNullableAll = false;
        }
        protected override ValidationResult IsValid(object value, ValidationContext validationContext)
        {
            var validateResult = false;
            var obj = validationContext.ObjectInstance;
            Type Ts = obj.GetType();
            var fields = _groupFields.Split(',');
            if (fields.Count() > 0)
            {
                for (var i = 0; i < fields.Count(); i++)
                {
                    var filedName = Convert.ToString(fields[i]);
                    if (string.IsNullOrEmpty(filedName)) continue;
                    //value
                    string filedValue = Convert.ToString(Ts.GetProperty(filedName).GetValue(obj, null));
                    //_notNullableAll=true，任意一個為空直接驗證掛掉跳出迴圈
                    if (_notNullableAll && string.IsNullOrWhiteSpace(filedValue))
                    {
                        validateResult = false;
                        break;
                    }
                    //_notNullableAll=false,只要有一個不為空就可以過驗證
                    if (!_notNullableAll && !string.IsNullOrWhiteSpace(filedValue))
                    {
                        validateResult = true;
                        break;
                    }
                }
            }
            //success
            if (validateResult)
                return ValidationResult.Success;
            else
            {
                //fail
                if (string.IsNullOrEmpty(ErrorMessage) && _notNullableAll)
                    return new ValidationResult($"{_groupFields}欄位全部不允許為空值");
                else if (string.IsNullOrEmpty(ErrorMessage) && !_notNullableAll)
                    return new ValidationResult($"{_groupFields}欄位中至少要有一個不為空的值");
                else
                    return new ValidationResult(ErrorMessage);
            }

        }
    }

    /// <summary>
    /// 組內資料同步判斷，同時為空或同時不為空通過驗證
    /// </summary>
    public class GroupEmptySyncAttribute : ValidationAttribute
    {
        private readonly string _groupFields;

        public GroupEmptySyncAttribute(string groupFields)
        {
            _groupFields = groupFields;
        }
        protected override ValidationResult IsValid(object value, ValidationContext validationContext)
        {
            var validateResult = true;
            var obj = validationContext.ObjectInstance;
            Type Ts = obj.GetType();
            var fields = _groupFields.Split(',');
            if (fields.Count() > 0)
            {
                bool firstValueIsEmpty = true;//第一個值是否為空
                for (var i = 0; i < fields.Count(); i++)
                {
                    var filedName = Convert.ToString(fields[i]);
                    if (string.IsNullOrEmpty(filedName)) continue;
                    //value
                    string filedValue = Convert.ToString(Ts.GetProperty(filedName).GetValue(obj, null));
                    //第一個值記錄是否為空
                    if (i == 0 && string.IsNullOrWhiteSpace(filedValue))
                        firstValueIsEmpty = true;
                    if (i == 0 && !string.IsNullOrWhiteSpace(filedValue))
                        firstValueIsEmpty = false;

                    //後續值判斷是否和第一個值符合，不符合直接結束驗證
                    if (i > 0)
                    {
                        if (string.IsNullOrWhiteSpace(filedValue) != firstValueIsEmpty)
                        {
                            validateResult = false;
                            break;
                        }
                    }
                }
            }
            //success
            if (validateResult)
                return ValidationResult.Success;
            else
            {
                //fail
                if (string.IsNullOrEmpty(ErrorMessage))
                    return new ValidationResult($"{_groupFields}欄位是否為空不一致（必須同時為空或同時不為空）");
                else
                    return new ValidationResult(ErrorMessage);
            }

        }
    }

    /// <summary>
    /// 判斷時間格式是否對應，時間格式一致通過驗證
    /// </summary>
    public class DateFormatValidAttribute : ValidationAttribute
    {
        private readonly string _formatStr;
        public DateFormatValidAttribute(string formatStr)
        {
            _formatStr = formatStr;
        }
        protected override ValidationResult IsValid(object value, ValidationContext validationContext)
        {
            var validateResult = false;
            try
            {
                //轉成要求的格式後 再和傳入的值對比
                var formatValue = Convert.ToDateTime((string)value).ToString(_formatStr);
                if ((string)value == formatValue)
                    validateResult = true;
                else
                    validateResult = false;

                //success
                if (validateResult)
                    return ValidationResult.Success;
                else
                {
                    //fail
                    if (string.IsNullOrEmpty(ErrorMessage))
                        return new ValidationResult($"時間格式不符合{_formatStr}格式");
                    else
                        return new ValidationResult(ErrorMessage);
                }
            }
            catch (Exception ex)
            {
                if (string.IsNullOrEmpty(ErrorMessage))
                    return new ValidationResult($"時間格式不符合{_formatStr}格式");
                else
                    return new ValidationResult(ErrorMessage);
            }
        }

    }
}
 

使用：

測試結果：

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