Umbraco Relations

RelationLookupType.cs

namespace MyProject.Models
{
    /// <summary>
    /// Enum RelationLookupType
    /// </summary>
    public enum RelationLookupType
    {
        Child,
        Parent
    }
}

RelationRepository.cs

using System.Collections.Generic;
using System.Linq;
using MyProject.Models;
using Our.Umbraco.Ditto;
using Umbraco.Core.Models;
using Umbraco.Core.Services;
using Umbraco.Web;

namespace MyProject.Repositories
{
    /// <summary>
    /// Class RelationRepository.
    /// </summary>
    public class RelationRepository
    {
        private readonly UmbracoHelper _umbracoHelper;
        private readonly ServiceContext _serviceContext;

        /// <summary>
        /// Initializes a new instance of the <see cref="RelationRepository" /> class.
        /// </summary>
        /// <param name="umbracoContext">The umbraco context.</param>
        /// <param name="serviceContext">The service context.</param>
        public RelationRepository(UmbracoContext umbracoContext, ServiceContext serviceContext)
        {
            _umbracoHelper = new UmbracoHelper(umbracoContext);
            _serviceContext = serviceContext;
        }

        /// <summary>
        /// Gets the related models.
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="content">The content.</param>
        /// <param name="relationAlias">The relation alias.</param>
        /// <param name="relationLookupType">Type of the relation lookup.</param>
        /// <returns>IList&lt;T&gt;.</returns>
        public IList<T> GetRelatedModels<T>(IPublishedContent content, string relationAlias, RelationLookupType relationLookupType = RelationLookupType.Child) where T : class
        {
            IEnumerable<IRelation> relations = null;
            switch (relationLookupType)
            {
                case RelationLookupType.Parent:
                    relations = _serviceContext.RelationService.GetByChildId(content.Id).Where(x => x.RelationType.Alias == relationAlias);
                    break;
                case RelationLookupType.Child:
                    relations = _serviceContext.RelationService.GetByParentId(content.Id).Where(x => x.RelationType.Alias == relationAlias);
                    break;
            }
            if (relations == null || !relations.Any()) return null;
            var relatedModels = MapRelatedModels<T>(relationLookupType, relations);

            return !relatedModels.Any() ? null : relatedModels;
        }

        /// <summary>
        /// Maps the related models.
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="relationLookupType">Type of the relation lookup.</param>
        /// <param name="relations">The relations.</param>
        /// <returns>List&lt;T&gt;.</returns>
        private List<T> MapRelatedModels<T>(RelationLookupType relationLookupType, IEnumerable<IRelation> relations) where T : class
        {
            var relatedModels = new List<T>();
            foreach (var relation in relations)
            {
                if (relation == null) continue;
                IPublishedContent node = null;
                switch (relationLookupType)
                {
                    case RelationLookupType.Child:
                        node = _umbracoHelper.TypedContent(relation.ChildId);
                        break;
                    case RelationLookupType.Parent:
                        node = _umbracoHelper.TypedContent(relation.ParentId);
                        break;
                }

                if (node == null) continue;
                relatedModels.Add(node.As<T>());
            }
            return relatedModels;
        }
        /// <summary>
        /// Determines whether the specified node has relations.
        /// </summary>
        /// <param name="nodeId">The node identifier.</param>
        /// <returns><c>true</c> if the specified node identifier has relations; otherwise, <c>false</c>.</returns>
        public bool HasRelations(int nodeId)
        {
            return _serviceContext.RelationService.GetByParentId(nodeId).Any();
        }
    }
}