how to create custom validation in mvc ?

I think interviewer do not want to use data annotation,

 

in this scenario you need to add your own validation class, and implement your logic under this class method:

 

but if you think for data annotation : then go for details:

 

ValidationAttribute class is included in DataAnnotations namespace. It helps you to validate model data received from user. It gives you many in built validation attributes like StringLength, Required, DataType for validating model.

 

http://dotnetmentors.com/mvc/how-to-do-custom-validation-using-validationattribute-of-aspnet-mvc.aspx

let's say,In validation we want the end date to be today's date instead of anyhardcode value. To achieve this we would be use

 

DateTime.Now.ToShortDateString() as shown below.

At this point, if you compile, you will get an error - An attribute argument must be a constant expression, typeof expression or array creation expression of an attribute parameter type.

 

To fix this, we can create a custom DateRangeAttribute. Here is the code.

 

Copy and paste the following code in DateRangeAttribute.cs class file.

Finally decorate "Joining Date" property with our custom DateRangeAttribute as shown below.

Using Data annotation is good practice but what is meant with custom data validation is that we have to mention the data annotationa long overriding the predefined function of validations. Like the link given below is overriding the validation check function for the isnull

 

https://stackoverflow.com/questions/16100300/asp-net-mvc-custom-validation-by-dataannotation 

System.ComponentModel.DataAnnotations namespace. is the correct answer, but The ValidationSummary can be used to display all the error messages for all the fields. It can also be used to display custom error messages.