Mappings between product line items

So this is a problem I've had to look up every time I have it, so I'm posting it here as a way to keep track. In order to map attributes between product line items (opportunity product to quote product to order product to invoice product), you have to access the secret mapping URL to set it up. Steps to perform:

1. Find the GUID of the mapping you need to edit. In the Org_MSCRM database, run this query:
select * from entitymapbase where targetentityname = 'salesorderdetail'
Obviously, you might need to change the target entity value - the above will return all of the relationships where the order line item is the target. This returns a column that shows the "source entity name", so for a mapping from quote product to order product, pick the line where the source is "quotedetail". Copy the EntityMapId from this row.

2. Enter the following URL into IE (modified with your servername):

http://[servername]/Tools/SystemCustomization/Relationships/Mappings/mappingList.aspx?mappingId=[GUID]

Be sure to replace your server name for CRM, and put the GUID from step 1 at the end.

3. Create mappings and repeat as necessary!