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Max & Min element validation for Content Area or Link Collection

Reccently we had a business requirement for setting minimum & maximum limit for blocks in Content Areas. While we can educate the content authors to set the correct number of blocks in the content area it's always recommended to add validation within the CMS to avoid human errors.

Here's the code to to set the maximum number of blocks in the content area and Link Item Collection. 

/// <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 : 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("This field exceeds the maximum limit of " + MaxCount + " items");
                }
            }
            else if (value is ContentArea)
            {
                if ((value as ContentArea).Count > MaxCount)
                {
                    return new ValidationResult("This field exceeds the maximum limit of " + MaxCount + " items");
                }
            }

            return null;
        }

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

On the Content Area field (or Link Item Collection) set the MaxElements attribute as shown below. 

[Display(
            Name = "Items",
            Description = "Items",
            GroupName = SystemTabNames.Content,
            Order = 30)]
        [MaxElements(25)]
        public virtual ContentArea Items { get; set; }

You can use the same logic for setting the minimum number of elements as well. 



Happy coding :)

Hi Aniket, first thanks for sharing this.

You should use the 'is' pattern matching in the code, see the docs. Now you first test is the value of some type (casting) and then if it was successful then the code casts again the object.

The XML comment says that it handles 'any other type of collection' but there is no implementation for collections in the code you have provided.

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