DataRelations. With or without the constraint?

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Guest

Why would you be able to (or want to), create a DataRelation without a
constraint? The DataRelation constructor takes a parent and child column
array to create the association, I assume (maybe incorrectly) that the child
column array would serve as the Foriegn Key. However, you need to set the
last parameter to TRUE to create the constraint in the child table. When
would you create a DataRelation without a FK constraint?

In SQL Server, can you create a DataRelation without a constraint?
 
Hi Michael,

In SQL Server, the relation and contraint are created together. Because a
database requires integrality. All data that goes into it must be valid.

However, the DataSet is not so strict. Sometimes people just need a
relation for them to find child rows. There can be some data whose value
does not follow the contraint, which means the constraint are not enforced.
This is a requirement for some apps, so the DataSet class must be flexible
enough to meet all the requirements.

If anything is unclear, please feel free to let me know.

Kevin Yu
Microsoft Online Community Support

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Thanks for your help. I guess that the DataRelation is sort of like putting 2
tables into a query designer and dragging a relation between tables. No
constraints there. Just the relation.

Adding the Constraint to the DataRelation is more akin to what occurs in SQL
Server when you create a relation with a FK constraint.

So, if I really only need the relation to retreive child rows, I don't need
the constraint created. If though I need child rows updated/deleted based on
what I due to a parent row, or if I need the sure that there are no orphan
child rows then I need the constraint.

Thanks
 
Hi Michael,

You can select what to create. Relation Only, FK constraint Only, or both.
Here are the steps:

1. Right click on the relation line in the DataSet designer and select
Properties from the context menu.
2. In the dialog box, you can choose what to create with the radio buttons.

Please try it and let me know the results. Thanks!

Kevin Yu
Microsoft Online Community Support
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(This posting is provided "AS IS", with no warranties, and confers no
rights.)
 
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