Multiple entities in Microsoft Dynamics CRM

var dialogId = "38D394F3-0C1B-46C5-A682-53F373501CBD";
var parentEntityLogicalName = "ar_parententity";

function Process(items) {
    if (items.length != 0) {
        var parentEntity = {};
        var parentEntityId;
        var parentEntityName;

        // Creating parent entity with some name
        parentEntity.ar_name = (new Date()).toString();
        SDK.JQuery.createRecord(
            parentEntity,
            parentEntityLogicalName,
            // call back from parent entity creating
            function (entity) {
                // saving parent entity id and name
                parentEntityId = entity.ar_parententityId;
                parentEntityName = entity.ar_name;

                // creating child entities
                for (var i = 0; i < items.length; i++) {
                    var childEntity = {};
                    childEntity.ar_name = (new Date()).toString();
                    // setting ParentEntity field to assotiate child entity with parent
                    childEntity.ar_ParentEntity = { Id: parentEntityId, LogicalName: parentEntityLogicalName, Name: parentEntityName };
                    // storing customer in child entity using the reference to customer
                    childEntity.ar_Customer = { Id: items[i].toString(), LogicalName: parentEntityLogicalName };
                    // creating record
                    SDK.JQuery.createRecord(
                        childEntity,
                        "ar_childentity",
                        function(chEntity) {},
                        errorHandler
                    );
                }

                // we didn't wait until all children will be created so starting dialog immediately after parent entity is created
                var serverUri = Mscrm.CrmUri.create('/cs/dialog/rundialog.aspx');
                window.showModalDialog(serverUri + '?DialogId=' + "%7b" + dialogId + "%7d" + '&EntityName=' + parentEntityLogicalName + '&ObjectId=' + parentEntityId,
                                null, 'dialogWidth: 615px; dialogHeight: 480px; resizable: yes; status: yes, scrollbars:yes;');
            },
            errorHandler
        );
    } else {
        alert("No records selected");
    }
}

function errorHandler(error) {
    alert(error.message);
}

using System;
using System.Linq;
using System.Text;

using Microsoft.Xrm.Sdk;
using Microsoft.Xrm.Sdk.Client;

using Xrm;

namespace ProcessMultipleRecords
{
    /// <summary>
    /// Process customers' invoices plugin
    /// </summary>
    public class ProcessCustomersPlugin : Plugin
    {
        /// <summary>
        /// Post operation pipeline stage.
        /// </summary>
        private const int PostOperationPipelineStage = 40;

        /// <summary>
        /// Create event name.
        /// </summary>
        private const string UpdateEventName = "Update";

        /// <summary>
        /// Assign customers to billing run trigger CRM name.
        /// </summary>
        private const string ParentEntityLogicalName = "ar_parententity";

        /// <summary>
        /// Initializes a new instance of the <see cref="ProcessCustomersPlugin"/> class.
        /// </summary>
        public ProcessCustomersPlugin()
            : base(typeof(ProcessCustomersPlugin))
        {
            this.RegisteredEvents.Add(
                new Tuple<int, string, string, Action<LocalPluginContext>>(
                    PostOperationPipelineStage, UpdateEventName, ParentEntityLogicalName, this.ExecuteProcessCustomers));
        }

        /// <summary>
        /// Executes customers processing.
        /// </summary>
        /// <param name="localPluginContext">
        /// The local plugin context.
        /// </param>
        private void ExecuteProcessCustomers(LocalPluginContext localPluginContext)
        {
            if (localPluginContext == null)
            {
                throw new ArgumentNullException("localPluginContext");
            }

            // Getting trigger entity
            ar_parententity trigger;
            if (localPluginContext.PluginExecutionContext.InputParameters != null
                && localPluginContext.PluginExecutionContext.InputParameters.Contains("Target")
                && localPluginContext.PluginExecutionContext.InputParameters["Target"] is Entity)
            {
                var entity = (Entity)localPluginContext.PluginExecutionContext.InputParameters["Target"];
                if (!entity.LogicalName.Equals(ar_parententity.EntityLogicalName))
                {
                    throw new ArgumentException("Plugin execution failure. Can not retrieve required reading.");
                }

                trigger = entity.ToEntity<ar_parententity>();
            }
            else
            {
                throw new ArgumentException("Plugin execution failure. Can not retrieve required reading.");
            }

            this.ProcessCustomers(trigger, localPluginContext);
        }

        /// <summary>
        /// Processes invoces connected to customers.
        /// </summary>
        /// <param name="trigger">
        /// The trigger with amount value.
        /// </param>
        /// <param name="localPluginContext">
        /// The local plugin context.
        /// </param>
        private void ProcessCustomers(ar_parententity trigger, LocalPluginContext localPluginContext)
        {
            using (var context = new PluginServiceContext(localPluginContext.OrganizationService))
            {
                // Getting Child Entities
                var triggerChildrens = context.ar_childentitySet.Where(x => x.ar_ParentEntity.Id == trigger.Id);
                foreach (var triggerChildren in triggerChildrens)
                {
                    // Getting customers from Child Entitites
                    var customer = context.ContactSet.FirstOrDefault(x => x.Id == triggerChildren.ar_Customer.Id);
                    if (customer != null)
                    {
                        // Getting invoices
                        var invoices =
                            context.InvoiceSet.Where(
                                x => x.CustomerId.Id == customer.Id && x.StateCode == InvoiceState.Active);
                        foreach (var invoice in invoices)
                        {
                            // Updating invoices
                            invoice.DiscountAmount =
                                new Money(
                                    (invoice.DiscountAmount ?? new Money(0)).Value
                                    + (trigger.ar_Amount ?? new Money(0)).Value);
                            context.UpdateObject(invoice);
                        }
                    }
                }

                // Saving all changes
                var results = context.SaveChanges(SaveChangesOptions.ContinueOnError);
                if (results.HasError)
                {
                    var sb = new StringBuilder();
                    foreach (var result in results)
                    {
                        if (result.Error != null)
                        {
                            sb.AppendFormat("{0}\n", result.Error.Message);
                        }
                    }

                    throw new InvalidOperationException(sb.ToString());
                }
            }
        }
    }
}