On 10/17/2013 08:32 AM, Sergey Mironov wrote:
The scheme is following:
(* Template.ur; page table is 'private' *)
table page : { Id : int, MenuText : string }
PRIMARY KEY Id
table product : { Id : int, Caption : string, Slogan : string, Logo :
string, PageId : int }
PRIMARY KEY Id
CONSTRAINT PageLink FOREIGN KEY PageId REFERENCES page(Id)
(* Template.urs declares only 'public' table, with no constraints *)
table product : { Id : int, Caption : string, Slogan : string, Logo :
string, PageId : int }
(* App.ur *)
val product = Template.product (* looks like table declarations don't
like dots in names. *)
Re: not liking dots, that's only the parsing sugar, which could
potentially be extended; though your approach here also seems reasonable
to me.
table featuret : { Id : int, Content: string, ProductId : int }
PRIMARY KEY Id,
CONSTRAINT ProductLink FOREIGN KEY ProductId REFERENCES product(Id)
The compiler doesn't allow this code.
There's a good reason the compiler doesn't like that code: the signature
of [Template] isn't enough to guarantee that you've written a valid SQL
table definition here! Foreign keys are only allowed to foreign fields
that are actually _keys_, and Ur/Web uses types to track the existence
of keys.
You'll need at least to indicate in Template.urs that [Id] is a key of
[product]. Currently that requires either (1) abandoning the [table]
syntactic sugar or (2) listing _all_ the constraints in Template.urs.
With (1), you can do (in Template.urs):
con product_constraints :: {{Unit}}
constraint [Pkey] ~ product_constraints
val product : sql_table [Id = int, Caption = string, Slogan =
string, Logo = string, PageId = int]
([Pkey = [Id]] ++ product_constraints)
[Actually, I had to add a small improvement to type inference to get the
example to work with only this change. You can pull the patch from the
public repo.]
It might be worth extending the [table] syntactic sugar to do something
like the above automatically; maybe I'll try it later.
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