ForeignKeyConstraint is a table-level definition, ForeignKey is a column level. If you have just a single ForeignKey on a single column, they are equivalent. for a composite foreign key, ForeignKeyConstraint gives you the extra verbosity needed (i.e. its exactly analgous to SQL's FOREIGN KEY clause which can be placed on a column or on the table overall).
"on_update" within ForeignKeyConstraint will place a "ON UPDATE=<something>" directive on your table's DDL definition. This is SQL level cascading and is described: http://www.postgresql.org/docs/8.1/interactive/sql-createtable.html (scroll down to "REFERENCES reftable [ ( refcolumn ) ]") the thing that "cascades" here is the update of a column value, such as UPDATE <sometable> SET x=5. the "cascade" flag on relation() also relates to the "cascading" of data along a relationship, but is talking about a relationship between two objects, and refers to various session operations such as save(), update(), delete(), etc. the thing that "cascades" here is a session call such as session.delete(x). so the term "cascade" refers to a general class of behavior (traversing along some kind of relationship), but has two totally different meanings in context (your database tables vs. a SQLAlchemy session object) --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To post to this group, send email to sqlalchemy@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy -~----------~----~----~----~------~----~------~--~---
