protected override ValidationResult IsValid(object value, ValidationContext validationContext) { var projectFile = (CreateProjectFileViewModel)validationContext.ObjectInstance; if (projectFile._projectFileName == null) { return(new ValidationResult("File name is required!")); } if (!_projectFileService.projectFileExists(projectFile._projectFileName, projectFile._projectID)) { return(ValidationResult.Success); } else { return(new ValidationResult("A file with this name is already in Project!")); } }