Sitecore package installation options explained
A lot of times there is some ignorance with developers about the possible package installation options. This also included myself. Sort of like an old habit I always use the "overwrite" option for data templates and layouts and the merge-clear option for content-items.
Looking at the description that is shown in the popup dialog during package installation, got me confused about the difference between the options and sub-options.
The descriptions of the installation options in the package installation wizard says:
| Overwrite | Replace the entire subtree with the subtree in the package |
| Merge - Clear | Leave the subtree and replace any matching items and versions with those from the package but do not replace any subitems. |
| Merge - Append | Leave the subtree. Overwrite nothing. Append any matching items to the existing subtree by giving them incremental numbers. |
| Merge - Overwrite | Leave the subtree and replace any matching items and versions with those from the package. |
| Skip | Take no action and move on to the next item. |
Looking at these descriptions, the Overwrite and Skip seem obvious although the description could be a bit better. But what about the merge-clear, merge-append and merge-overwrite? Those got me really confused.
The correct description of what each option does should be something like this:
| Overwrite | Items with the same ID (along with it's descendants) will be removed and replaced by items from the package. |
| Skip | Items with the same ID from the target database will remain unchanged; the item from the package will be skipped. |
| Merge - Clear | all existing versions for a language of the item being installed are removed prior to adding new versions. This options 'clears out' the versions of the language and creates one new version. |
| Merge - Append | item versions from the package are added 'on-top' of the existing versions of the item. This preserves history, but numbers the package versions with numbers higher than the existing version numbers. A user can merge information between versions afterwards. |
| Merge - Merge | if there is a version with the same number in the item, the Installation Wizard will overwrite it, otherwise a new version with the specific number is added. This makes it possible to replace specific versions of items. |
As you can see, the Merge-options doesn't remove items, but instead, merges versions of an item.
The Merge-Append option could be useful when updating content from a testing or acceptance environment to a production environment (or vice versa) where the customer has already started creating content without losing any of the previous content.