Razor Model Validation

Model Validation Annotation

Including Combined validations by using IValidatableObject

  public class RenewPracticeDetails : IValidatableObject
    {
        public string LegalName { get; set; }
        [Required(ErrorMessage = "The Name of the Practice as it appears on your bank statement field is required.")]
        public string LegalNameOnStatement { get; set; }
      
        public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
        {
            var controlName = new List<string>();
            if (TradingStatus == 3 && string.IsNullOrEmpty(LPNumber))
            {
                controlName.Add("LPNumber");
                yield return new ValidationResult("You must supply a LP Number", controlName);
            }
            if (TradingStatus == 4 && string.IsNullOrEmpty(LLPNumber))
            {
                controlName.Add("LLPNumber");
                yield return new ValidationResult("You must supply a LLP Number", controlName);
            }
        }
    }

in CSHTML

                            @Html.TextBoxFor(m=> m.LegalNameOnStatement, "", new { @class = "form-control" })
                            @Html.ValidationMessage("LegalNameOnStatement")

                            <div class="radio" id="div_4" >
                                <fieldset>
                                    <label class="control-label radioLabel" for="llpNumber">LLP Number</label>
                                    @Html.TextBoxFor(m => m.LLPNumber, "", new { @class = "form-control" })
                                    @Html.ValidationMessage("LLPNumber")
                                </fieldset>
                            </div>

Controller

   [HttpPost]
   public async Task<IActionResult> PracticeDetails(RenewPracticeDetails renewPracticeDetails)
   {
      if (ModelState.IsValid)
      {
      ....
      }
      return View(renewPracticeDetails);
   }