[Ur] solution to the DB chicken and egg problem?

[Marko Schütz Schmuck]

On Sun, 02 Apr 2017 09:02:15 -0400,
Adam Chlipala wrote:
> 
> Actually, Ur/Web won't even accept those table definitions: no mutually recursive
> definitions yet, w.r.t. constraints.  And I haven't thought before about allowing
> temporary breaking of constraints.

"Constraints hold after every statement" -> "Constraints hold after
every transaction"?

> On 04/02/2017 08:35 AM, Marko Schütz Schmuck wrote:
> > If I have tables
> > 
> > table chicken : { Id : int, Egg : int }
> >        PRIMARY KEY (Id),
> >        CONSTRAINT egg FOREIGN KEY Egg REFERENCES egg(Id)
> > 
> > table egg : { Id : int, Chicken : int }
> >        PRIMARY KEY (Id),
> >        CONSTRAINT chicken FOREIGN KEY Chicken REFERENCES chicken(Id)
> > 
> > Outside of Ur/Web this would be solved by setting the constraints
> > DEFERRABLE INITIALLY DEFERRED and do the INSERTs pairwise inside a
> > single transaction.
> > 
> > I doubt that there currently is a way to do this in Ur/Web since there
> > is neither a way to specify DEFERRABLE INITIALLY DEFERRED nor a way to
> > explicitly form transactions.
> > 
> > Would it be enough to introduce an operator
> > 
> > dml_sequence : dml -> dml -> dml
> > 
> > allowing two dml statements to be composed and run in a single
> > transaction together with exposing DEFERRABLE INITIALLY DEFERRED at
> > the Ur/Web language level?
> > 
> > Best regards,
> > 
> > Marko
> 
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