Show/hide blocks and properties based on selected site in multi-site solution

Optimizely PaaS CMS has a great support for multi-site solutions which can additionally be extended with the custom code. For example, we can enhance it to show or hide entire blocks or blocks elements based on the selected site in a multi-site setup. This enables tailored content experiences across different domains while maintaining a single content structure.

First let's create enum with list of our sites, it should match site definition names in CMS Settings -> Manage Websites panel:

public enum MySite
{
    Site1,
    Site2,
    Site3
}

We will also need a helper class to resolve a site based on current host name and port (helpful for local development):

public interface ISiteHelper
{
    public MySite GetCurrentSite();
}

public class SiteHelper : ISiteHelper
{
    private readonly ISiteDefinitionResolver _siteDefinitionResolver;
    private readonly IHttpContextAccessor _httpContextAccessor;

    public SiteHelper(ISiteDefinitionResolver siteDefinitionResolver, IHttpContextAccessor httpContextAccessor)
    {
        _siteDefinitionResolver = siteDefinitionResolver;
        _httpContextAccessor = httpContextAccessor;
    }

    public MySite GetCurrentSite()
    {
        var request = _httpContextAccessor.HttpContext?.Request;
        var host = request?.Host.Host;
        if (request.Host.Port != null)
        {
            host += ":" + request.Host.Port;
        }
        var siteDefinition = _siteDefinitionResolver.GetByHostname(host, true);

        if (siteDefinition != null)
        {
            foreach (var name in Enum.GetNames(typeof(MySite)))
           {
               if (siteDefinition.Name.Equals(name, StringComparison.InvariantCultureIgnoreCase))
               {
                   return (MySite)Enum.Parse(typeof(MySite), name);
               }
           }
        }
        throw new Exception($"Site not cunfigured for host {host}");
    }
}

Next we can implement an attribute which utilizes the helper class described above. Besides hiding the element, we want to ensure that if property is required but should be hidden validation logic won't be execured for that site:

public class ShowOnSitesAttribute : Attribute, IDisplayMetadataProvider
{
    private readonly MySite[] _sites;
    private readonly ISiteHelper _siteHelper;
    public bool Hide => !_sites.Contains(_siteHelper.GetCurrentSite());
    
    public ShowOnSitesAttribute(params MySite[] sites)
    {
        _sites = sites;
        _siteHelper = ServiceLocator.Current.GetService();
    }

    public void CreateDisplayMetadata(DisplayMetadataProviderContext context)
    {
         if (_sites.Contains(_siteHelper.GetCurrentSite()))
        {
            return;
        }

        var extendedMetadata = context.DisplayMetadata.AdditionalValues[ExtendedMetadata.ExtendedMetadataDisplayKey] as ExtendedMetadata;
        if (extendedMetadata == null)
        {
            return;
        }

        extendedMetadata.ShowForEdit = false;
        foreach (var property in extendedMetadata.Properties)
        {
            property.IsRequired = false;
            property.ValidationMetadata.IsRequired = false;
        }
    }
}

Finally we can use the attribute in a block for entire class or for the properties:

[ContentType(DisplayName = "My Block", GUID = "A4ED27A1-2B34-4323-885E-4B478A137578")]
[ShowOnSites(MySite.Site1, MySite.Site2)]
public class MyBlock : BlockData
{
    [CultureSpecific]
    [Required]
    [Display(Name = "Heading", GroupName = TabNames.Content, Order = 10)]
    [ShowOnSites(MySite.Site1)]
    public virtual string Heading { get; set; }

    [CultureSpecific]
    [Display(Name = "Description", GroupName = TabNames.Content, Order = 20)]
    public virtual XhtmlString Description { get; set; }
}