table protein does not have an attribute oid? why?

Dear All:



I want to create a delete cascade in children tables.  The primary key of 
parent table is oid.




CREATE TABLE Link (   Protein_ID oid,   Link varchar(128)   CONSTRAINT one   REFERENCES Protein (oid)   ON DELETE
CASCADE
);

Create child table is ok.

When I insert a record into this child table, it says
"ERROR: constraint one: table protein does not have an attribute oid"

Why?


Thanks.



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