how do you set same error message for all required attribute validation?

Question

I am new to .net core. The following code changes all required validation message to "This field is required" for asp.net framework.

 public class CustomRequiredAttribute:RequiredAttribute, IClientValidatable
    {

        public override bool IsValid(object value)
        {
            return base.IsValid(value);
        }

        public override string FormatErrorMessage(string name)
        {
            return base.FormatErrorMessage(name); // expandable to format given message later
        }

        public IEnumerable<ModelClientValidationRule> GetClientValidationRules(ModelMetadata metadata, ControllerContext context)
        {
            return new[] { new ModelClientValidationRule { ErrorMessage = "This field is required", ValidationType = "required" } };
        }
    }

How do you do same for .net core?

 public class CustomRequiredAttribute:RequiredAttribute
    { 
      //set required field message to : This field is requried.
    }

Answer 1

For your requirement, you could implement RequiredAttribute, IClientModelValidator like

public class DefaultRequiredAttribute: RequiredAttribute, IClientModelValidator
{
    public DefaultRequiredAttribute()
    {
        ErrorMessage = "This field is required";
    }

    public void AddValidation(ClientModelValidationContext context)
    {
        MergeAttribute(context.Attributes, "data-val", "true");
        MergeAttribute(context.Attributes, "data-val-required", ErrorMessage);
    }
    private bool MergeAttribute(IDictionary<string, string> attributes, string key, string value)
    {
        if (attributes.ContainsKey(key))
        {
            return false;
        }

        attributes.Add(key, value);
        return true;
    }
}

And use like

public class Product
{
    public int Id { get; set; }
    public string Name { get; set; }
    [DefaultRequired]
    public string UserImage { get; set; }
}