如何限制内容区域中使用的块类型的数量？

Question

我有一个块类型，用于特定页面的特定内容区域。有什么方法可以验证（在页面级别或内容区域级别）该块未被多次使用？

Answer 1

没有内置内容，但您可以轻松连接到 SavingContent 或 PublishingContent 事件并在 saved/published 之前验证内容。

Answer 2

这是一个示例验证属性 class，应该会有帮助。我正在开发一个 "Validation Rules" nuget 包，我认为它可以包括这个。我只包含了 "Min by object type" 规则，但在发布之前会添加更多规则。

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}";
        }
    }
}

内容区域的示例应用程序：

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

无效时在编辑器视图中的结果（阻止发布）：

如何限制内容区域中使用的块类型的数量？

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

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