Hello SftwDude and Jon,

Yes, indeed. You are right. The warning message "DBML1062" is due to the
lack of PK in the table tblPart. We also received several reports of this
problem in MSDN forum:
http://forums.microsoft.com/MSDN/ShowPost.aspx?PostID=2510382&SiteID=1
http://forums.microsoft.com/MSDN/ShowPost.aspx?PostID=2896891&SiteID=1
And the resolution is to, as Jon said, add a PK to the table.

SftwDude, though the second table (tblPart) does not contain any fields
that are unique, we can add a PK to it in one of the following ways:

Method 1. Add an int-typed column (e.g. tblPartID) to the table tblPart,
and fill the value 1, 2, 3, 4¡­ to this column for the existing items. Then
set the PartID column as PK, and set its Identity Specification as True in
SQL Server Table designer so that when new item is inserted into the table,
the value of PartID could be automatically generated.

Method 2. In the table tblPart, if multiple columns together (e.g. the
combination of part number and part name) can identify one item, we can
turn the fields into a PK:
alter table tblPart add constraint applied_tags_PK primary key
(part_number, part_name);

If you have any other concerns or questions, please feel free to let me
know.

Regards,
Jialiang Ge (jialge@online.microsoft.com, remove 'online.')
Microsoft Online Community Support

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Thanks Jon and Jialiang.

It added an Identity field and made it a Primary Field as you suggested.
This works, now I get the power of having non flat entity and having the
DataContext managing CRUD and concurrency, etc...

I was reluctant to add a field to the table that is not necessary, but the
benefit out ways the additional field.

Thanks again