List relationship is a new concept in SharePoint 2010 which allows you to have one list have a lookup into another one and if delete is performed on the dependent items – you can either choose to perform cascade delete or restrict deletion.
To set this up using UI, you need to pick Main and Dependent list, then establish a lookup in your Dependent that will point to a field in Main list, and right away you will see the options similar to below:
Now, if you`re like me … you will probably want to configure this setting through solution deployment and not ask your users to perform manual configuration. Here is how to do that:
Note: We`ll use SharePoint 2010 Blog template which has Posts and Comments making them two dependent lists. I want to delete all of the comments when user deletes posts (out of the box comments remain undeleted).
1. Copy Blog Template (C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\TEMPLATE\SiteTemplates\Blog) to your Blank SharePoint solution in Visual Studio 2010.
2. Open Blog->Lists->Comments->Schema.xml
3. Find the following field definition and add the highlighted part to it:
<Field Name=”PostTitle” Type=”Lookup” Required=”TRUE” DisplayName=”$Resources:comments_schema_blgfld_posttitle;” List=”$Resources:core,lists_Folder;/$Resources:core,blogpost_Folder;” ShowField=”Title” ID=”{a131e489-d3d6-4f0c-a152-a3beb89f12be}” Indexed=”TRUE” RelationshipDeleteBehavior=”Cascade” Sealed=”TRUE” SourceID=”http://schemas.microsoft.com/sharepoint/v3″ StaticName=”PostTitle”>
Note that I also have Indexed=”TRUE” in my field definition, now this is because each column that will have relationship with other list`s field has to be indexed – to speed up underlying processing.
Example of Blog site template is a great pattern to follow when you need to define your own relationship between lists.
Here is some more on the field usage.
Enjoy!
