Glass Mapper Validate Required Field

ValidateItemTask.cs

public class ValidateItemTask : IObjectConstructionTask
{
    private bool IsValid(ObjectConstructionArgs args)
    {
        var context = (SitecoreTypeCreationContext) args.AbstractTypeCreationContext;
        var service = (SitecoreService)args.Service;

        var requiredFields = GetRequiredFields(args);
        foreach (var requiredField in requiredFields)
        {
            var field = Utilities.GetField(context.Item, requiredField.FieldId, requiredField.FieldName);

            // If the field does not exist it is not valid.
            if (field == null)
                return false;

            // If the field value is empty it is not valid.
            var value = field.GetValue(true, true);
            if (string.IsNullOrEmpty(value))
                return false;

            // Perform type specific checks.
            switch (field.Type)
            {
                case "Checkbox":
                case "Date":
                case "Datetime":
                case "Integer":
                case "Number":
                case "Multi-Line Text":
                case "Password":
                case "Rich Text":
                case "Single-Line Text":
                    break;
                case "General Link":
                case "General Link with Search":
                    {
                        var linkField = ((LinkField) field);
                        if (linkField.IsInternal)
                        {
                            var item = linkField.TargetItem;
                            if (item == null || item.Versions.Count == 0)
                                return false;
                        }
                        else if (linkField.IsMediaLink)
                        {
                            var item = linkField.TargetItem;
                            if (item == null)
                                return false;
                        }
                        break;
                    }
                case "Grouped Droplink":
                case "Droplink":
                case "Droptree":
                    {
                        ID itemId;
                        if (!ID.TryParse(value, out itemId))
                            return false;
                        var item = service.Database.GetItem(itemId);
                        if (item == null || item.Versions.Count == 0)
                            return false;
                        break;
                    }
                case "Multilist":
                case "Multilist with Search":
                case "Checklist":
                case "Searchable Tree List":
                case "Treelist":
                case "TreelistEx":
                case "ItemAggregate":
                    {
                        var itemIds = ID.ParseArray(value);
                        var exists = itemIds.Select(itemId => service.Database.GetItem(itemId))
                               .Any(item => item != null && item.Versions.Count != 0);
                        if (!exists)
                            return false;
                        break;
                    }
                case "File":
                    {
                        FileField fileField = field;
                        if (fileField.MediaItem == null)
                            return false;
                        break;
                    }
                case "Image":
                    {
                        ImageField imageField = field;
                        if (imageField.MediaItem == null)
                            return false;
                        break;
                    }
                default:
                    throw new NotImplementedException(string.Format("Support for the field type '{0}' has not been implemented.", field.Type));
            }
        }
        return true;
    }
}