Allan Thraen
Nov 27, 2017
(2 votes)

Limit number of elements in a LinkItemCollection or ContentArea

A colleague asked me today how to ensure that editors don't add too many elements in a LinkItemCollection or ContentArea - since too many could potentially break the design. I figured a simple validation attribute could do the trick - and sure enough, it can. I figured I'd share it here as it's a nice example of how to do custom validations of property values. I could have extended it even further to also ensure that the front-end code wouldn't even allow for the editor to try and drop an element if there's already too many - but due to time restraints and my limited dojo-skills, I simply left that part as a fun TODO for all of you out there. If you have that part, feel free to share in the comments...

Here is the main class:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.ModelBinding;
using EPiServer.Core;
using EPiServer.ServiceLocation;
using EPiServer.Shell.ObjectEditing;
using System.ComponentModel.DataAnnotations;
using System.Diagnostics.CodeAnalysis;
using EPiServer.SpecializedProperties;

namespace ExperimentsValidationAttributes
    /// <summary>
    /// Sets the maximum element count in a linkcollection, a content area - or any other type of collection.
    /// </summary>
    [AttributeUsage(AttributeTargets.Property, AllowMultiple = false)]
    public class MaxElementsAttribute : System.ComponentModel.DataAnnotations.ValidationAttribute, IMetadataAware
        public int MaxCount { get; set; }

        public void OnMetadataCreated(ModelMetadata metadata)
            //TODO: Use to disable editor drag and drop at a certain point.

        protected override ValidationResult IsValid(object value, ValidationContext validationContext)
            if (value == null)
                return null;
            if(value is LinkItemCollection)
                if((value as LinkItemCollection).Count > MaxCount)
                    return new ValidationResult("Too many Link Items in the collection. Maximum is " + MaxCount);
            } else if(value is ContentArea)
                if((value as ContentArea).Count>MaxCount)
                    return new ValidationResult("Too many content items in content area. Maximum is " + MaxCount);

            return null;

        public MaxElementsAttribute(int MaxElementsInList)
            this.MaxCount = MaxElementsInList;

And of course it's straightforward to use:

        public virtual LinkItemCollection Links { get; set; }

            GroupName = SystemTabNames.Content,
            Order = 320)]
        public virtual ContentArea MainContentArea { get; set; }
Nov 27, 2017


valdis Nov 28, 2017 10:16 AM

cool. also, similar - if you are using Bootstrap and want to notify editors that too much items in that content area might blow up something - you can use very similar validator.

Robert Runge
Robert Runge Nov 29, 2017 10:05 AM

Nice. Does this take into consideration the use of visitor groups?

I might want maximum five elements per visitor group - and not in all.

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