NestedContentCreator - generate a NestedContent Property Value based on a Property Type and a list of dictionary items.

NestedContentCreator.cs

using Newtonsoft.Json;
using Newtonsoft.Json.Linq;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using Umbraco.Core;
using Umbraco.Core.Models;
using Umbraco.Core.Models.Editors;
using Umbraco.Core.PropertyEditors;

namespace RMS.Extensions.Importers
{
    public static class NestedContentCreator
    {

        public static List<object> GenerateNestedContentList(PropertyType property, IEnumerable<Dictionary<string, object>> data)
        {
            var contentType = GetContentType(property.DataTypeDefinitionId);
            
            List<object> nodes = new List<object>();
            foreach (var item in data)
            {
                nodes.Add(GenerateNestedContentItem(contentType, item));
            }

            return nodes;
        }

        public static string GenerateNestedContentValue(PropertyType property, IEnumerable<Dictionary<string, object>> data)
        {
            return JsonConvert.SerializeObject(GenerateNestedContentList(property, data));
        }

        public static object GenerateNestedContentItem(IContentType contentType, Dictionary<string, object> propertyData)
        {
            // Update template and populate.
            var propValues = new JObject();

            foreach (var propKey in propertyData.Keys)
            {
                var propType = contentType.PropertyTypes.FirstOrDefault(x => x.Alias == propKey);
                if (propType == null)
                {
                    if (propKey != "name")
                    {
                        // Property missing so just delete the value
                        propValues[propKey] = null;
                    }
                }
                else
                {
                    // Fetch the property types prevalue
                    var propPreValues = ApplicationContext.Current.Services.DataTypeService.GetPreValuesCollectionByDataTypeId(propType.DataTypeDefinitionId);

                    // Lookup the property editor
                    var propEditor = PropertyEditorResolver.Current.GetByAlias(propType.PropertyEditorAlias);

                    // Create a fake content property data object
                    var contentPropData = new ContentPropertyData(
                        propertyData[propKey] == null ? null : propertyData[propKey].ToString(), propPreValues,
                        new Dictionary<string, object>());

                    // Get the property editor to do it's conversion
                    var newValue = propEditor.ValueEditor.ConvertEditorToDb(contentPropData, propValues[propKey]);

                    // Add the property
                    propValues[propKey] = (newValue == null) ? null : JToken.FromObject(newValue);
                }
            }

            return propValues;
        }

        private static IContentType GetContentType(int propertyDefinitionId)
        {
            var preValueCollection = (PreValueCollection)ApplicationContext.Current.ApplicationCache.RuntimeCache.GetCacheItem(
                string.Concat("Our.Umbraco.NestedContent.GetPreValuesCollectionByDataTypeId_", propertyDefinitionId),
                () => ApplicationContext.Current.Services.DataTypeService.GetPreValuesCollectionByDataTypeId(propertyDefinitionId));

            var preValuesDict = preValueCollection.PreValuesAsDictionary.ToDictionary(x => x.Key, x => x.Value.Value);

            Guid contentTypeGuid;
            if (!preValuesDict.ContainsKey("docTypeGuid") || !Guid.TryParse(preValuesDict["docTypeGuid"], out contentTypeGuid))
                return null;

            var contentTypeAlias = GetContentTypeAliasByGuid(Guid.Parse(preValuesDict["docTypeGuid"]));
            return ApplicationContext.Current.Services.ContentTypeService.GetContentType(contentTypeAlias);
        }

        private static string GetContentTypeAliasByGuid(Guid id)
        {
            return (string)ApplicationContext.Current.ApplicationCache.RuntimeCache.GetCacheItem(
                string.Concat("Our.Umbraco.NestedContent.GetContentTypeAliasByGuid_", id),
                () => ApplicationContext.Current.DatabaseContext.Database
                    .ExecuteScalar<string>("SELECT [cmsContentType].[alias] FROM [cmsContentType] INNER JOIN [umbracoNode] ON [cmsContentType].[nodeId] = [umbracoNode].[id] WHERE [umbracoNode].[uniqueID] = @0", id));
        }

    }
}

NestedContentCreatorExampleUsage.cs

            // showbag is of type IContent.
            var pt = showbag.PropertyTypes.FirstOrDefault(p => p.Alias == "locations");

            // db is an EntityFramework CodeFirst database, with a table rasv_ShowbagStallLocation.
            // In this example I want to take all locations related to the showbag and import them as a NestedContent list.
            
            // Create and serialise the Showbag Locations
            showbag.SetValue(pt.Alias, NestedContentCreator.GenerateNestedContentValue(pt,
                    db.rasv_ShowbagStallLocation
                                        .Where(i => i.ShowbagId == showbagId)
                                        .ToList()
                                        .Select(location => new Dictionary<string, object>
                                            {
                                                {"location", location.ShowbagLocationHTML},
                                                // EnsureEventPrecinct is another method that effectively 
                                                // maps the EvenTPrecinctId to a Content Node.
                                                {"eventPrecinct", EnsureEventPrecinct(location.EventPrecinctId).Id}
                                            }
                                        )));