ASP.NET Core Web API - How to validate EndDate greater than StartDate in EF

Question

In my ASP.NET Core Web API Entity Framework Data Annotaion Code first, I have this code in DTO (Data Transformation Object):

[DataType(DataType.Date)]
[Display(Name = "Start Date")]
[Required(ErrorMessage = "Start Date is Required")]
[JsonProperty(PropertyName = "StartDate")]
public DateTime StartDate { get; set; }

[DataType(DataType.Date)]
[Display(Name = "End Date")]
[Required(ErrorMessage = "End Date is Required")]
[JsonProperty(PropertyName = "EndDate")]
public DateTime EndDate { get; set; }

How do I validate that EndDate must be greater than StartDate?

Thank you

Answer 1

You can add custom validation logic by implementing the IValidatableObject on your DTO class. Aside from adding the interface to your class definition, add the following method:

public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
{
    // if either date is null, that date's required attribute will invalidate
    if (StartDate != null && EndDate != null && StartDate >= EndDate)
        yield return new ValidationResult("EndDate is not greater than StartDate.");
}