Merge Sitecore layout details using XmlDeltas

One of the features that Sitecore introduced somewhere in the Sitecore 6.x range is “Layout Deltas“,  the possibility to merge an item’s layout details with the layout details on the item’s __Standard Values template.

It means that you can add sublayouts to the __Standard Values, and still modify the sublayouts on the actual item, without overwriting __Standard Values.

Because instead of copying all the layout details from the __Standard Values, Sitecore will only keep a difference list on the item, not the entire layout details. Sitecore then uses the XmlDeltas field type to merge the two.

If you look at the raw values in Sitecore, you will see that in the “Layout” field of your __Standard values, the contents look like this:

<r xmlns:xsd="http://www.w3.org/2001/XMLSchema" >
  <d id="{FE5D7FDF-89C0-4D99-9AA3-B5FBD009C9F3}" l="{45D794F6-9DBB-4DBE-9826-606456562FB4}">
    <r id="{153F8C66-033E-456A-9C5F-A98D587C7A7E}" ph="" uid="{DE3402CB-9E79-4539-8C54-1DA8FB8D3733}" />
    <r ds="" id="{69EB7A6D-ACEF-4D06-A923-804918AA245E}" par="" ph="NewsletterHeadSection" uid="{CECCDC8D-3AF8-448D-A527-F8471C139FE9}" />
    <r id="{424A40CD-CAF3-45D9-87BA-CBE88C895A64}" ph="" uid="{48640574-E4FB-433B-97B4-0B202D609CB2}" />
    <r ds="" id="{A5975387-6B3A-4A43-BDF5-2A422057E518}" par="" ph="NewsletterBody" uid="{56CA9222-D31E-400A-B697-B620CF431DFF}" />
    <r id="{E429A2F3-DCFC-416E-ACB1-6BB7DE70C846}" ph="" uid="{7DBE3A38-12AD-42B7-8115-F50121D38B84}" />
    <r ds="" id="{175839E3-AEF4-4830-B679-0F51B90B438E}" par="" ph="NewsletterFooter" uid="{DA53887E-B21F-4C8B-A7D7-C3770B79DDF3}" />
  </d>
</r>

But the “Layout” field of the actual item look like this:

<r xmlns:p="p" xmlns:s="s" p:p="1">
  <d id="{FE5D7FDF-89C0-4D99-9AA3-B5FBD009C9F3}">
    <r uid="{7B831873-DE0D-46AA-AA38-9B5A72A3A1B7}" p:before="r[@uid='{7DBE3A38-12AD-42B7-8115-F50121D38B84}']" s:ds="{C57FBE62-5181-49B8-BF6A-E7CEE7BED209}" s:id="{7CCB9656-AE33-4609-92F0-1FDC5632BB8B}" s:ph="newsletterbody" />
  </d>
</r>

Notice the p:before attribue in the last XML? These are the attributes telling Sitecore how to apply the changes to the finished layout details.

You can do the merge yourself using the XmlDeltas field. This example merges the __Standard values onto the item itself:

using Sitecore.Data;
using Sitecore.Data.Fields;
using Sitecore.Data.Items;

/// <summary>
/// Merge layouts
/// </summary>
/// <param name="destinationItem">Item that receives the merged layouts</param>
/// <param name="standardItem">Item to merge from (the Standard Values usually)</param>
private string MergeLayouts(Item destinationItem, Item standardItem)
{
  LayoutField layoutDestinationItem = destinationItem.Fields[Sitecore.FieldIDs.LayoutField];
  LayoutField layoutStandardItem = standardItem.Fields[Sitecore.FieldIDs.LayoutField];
  string deltaLayout = XmlDeltas.ApplyDelta(layoutDestinationItem.Value, layoutStandardItem.Value);
  destinationItem.Editing.BeginEdit();
  try
  {
    destinationItem.Fields[Sitecore.FieldIDs.LayoutField].Value = deltaLayout;
    destinationItem.Editing.EndEdit();
    return deltaLayout;
  }
  catch (Exception ex)
  {
    destinationItem.Editing.CancelEdit();
    throw new Exception("Updating '" + destinationItem.Paths.FullPath + "' failed: " + ex.ToString());
  }
}

It is the XmlDeltas.ApplyDelta that executes the merging.

Please notice that if you merge from __Standard Values, and later modify the item that was merges, Sitecore will identify the merge, and “unmerge” your merged item. It does so using the XmlDeltas.GetDelta() method:

string deltaLayout = XmlDeltas.GetDelta(layoutDestinationItem.Value, layoutStandardItem.Value);

MORE INFORMATION:

• Complex layouts in Sitecore using standard values hierarchy by Cognifide.
• Unsharing the Layout field in Sitecore – a multi-language strategy by Jan Hebnes
• What is Layout Deltas by Adam Conn