How to restrict the number of a blocktype used in contentarea?

Question

I have a block type which I am using on a specific content area on a specific page. is there any way that I can validate(on page level or contentarea level) that block is not used more than once?

Do you want to make sure there is only one block in the content area, one block of that type (but with possibly multiple other types), or both? I think this can be done with a validation decorator pretty readily without the event hooks below. — egandalf, Jul 25 '17 at 13:50

score 3 · Accepted Answer · answered Jul 25 '17 at 17:21

Here's a sample validation attribute class that should help. I am working on a "Validation Rules" nuget package that I thought could include this. I only included the "Min by object type" rule but will add more before it's released.

Class:

using EPiServer;
using EPiServer.Core;
using EPiServer.ServiceLocation;
using System;
using System.ComponentModel.DataAnnotations;
using System.Reflection;

namespace eGandalf.Epi.Validation.Lists
{
    /// <summary>
    /// Detects whether the minimum required items of a specific type within a ContentArea condition has been met. Only supports items that can be loaded by IContentLoader. Supports type inheritance.
    /// </summary>
    [AttributeUsage(AttributeTargets.Property | AttributeTargets.Field, AllowMultiple = true, Inherited = true)]
    public class MinimumOfTypeAttribute : ValidationAttribute
    {
        public int Limit { get; }
        public Type ObjectType { get; }

        public MinimumOfTypeAttribute(int limit, Type t)
        {
            Limit = limit;
            ObjectType = t;
        }

        public override bool IsValid(object value)
        {
            if (value == null && Limit > 0) return false;

            var area = value as ContentArea;
            if (area != null) return ValidateContentArea(area);

            throw new TypeMismatchException("Minimum of type only works with ContentArea properties.");
        }

        private bool ValidateContentArea(ContentArea area)
        {
            if (area?.Items?.Count < Limit) return false;

            var typeCount = 0;
            foreach (var item in area.Items)
            {
                if (CanLoadContentByType(item.ContentLink))
                {
                    typeCount++;
                    // Return as soon as the validation is true.
                    if (typeCount >= Limit) return true;
                }
            }
            return false;
        }

        private bool CanLoadContentByType(ContentReference reference)
        {
            var loader = ServiceLocator.Current.GetInstance<IContentLoader>();
            var loaderType = loader.GetType();
            MethodInfo getMethod = loaderType.GetMethod("Get", new Type[] { typeof(ContentReference) });
            MethodInfo genericGet = getMethod.MakeGenericMethod(new[] { ObjectType });

            try
            {
                var content = genericGet.Invoke(loader, new object[] { reference });
                return content != null;
            }
            catch (Exception ex)
            {
                return false;
            }
        }

        public override string FormatErrorMessage(string name)
        {
            return $"ContentArea {name} must include at least {Limit} items of type {ObjectType.Name}";
        }
    }
}

Sample application on a content area:

[MinimumOfType(1, typeof(RssReaderBlock))]
public virtual ContentArea RelatedContentArea { get; set; }

Result in editor view when invalid (prevents publish):

score 1 · Answer 2 · edited Jun 17 '17 at 17:37

1

Nothing built-in, but you can easily hook up to the SavingContent or PublishingContent events and validate content before it's saved/published.

Examples here and there.

edited Jun 17 '17 at 17:37

Billal Begueradj

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answered Jun 16 '17 at 15:17

Ted Nyberg

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How to restrict the number of a blocktype used in contentarea?

2 Answers2