[SQL-CVS] r1445 - SQLObject/docs

[<sub...@co...>]

Author: phd
Date: 2005-12-30 20:36:19 +0000 (Fri, 30 Dec 2005)
New Revision: 1445

Modified:
   SQLObject/docs/FAQ.txt
Log:
Documented using applyConstraints for mutually referencing tables.


Modified: SQLObject/docs/FAQ.txt
===================================================================
--- SQLObject/docs/FAQ.txt	2005-12-30 20:18:32 UTC (rev 1444)
+++ SQLObject/docs/FAQ.txt	2005-12-30 20:36:19 UTC (rev 1445)
@@ -391,3 +391,35 @@
 The reason for this limit is that each object needs a database ID, and
 in many databases you cannot attain an ID until you create a row.
 
+Mutually referencing tables
+---------------------------
+
+How can I create mutually referencing tables? For the code::
+
+    class Person(SQLObject):
+        role = ForeignKey("Role")
+
+    class Role(SQLObject):
+        person = ForeignKey("Person")
+
+    Person.createTable()
+    Role.createTable()
+
+Postgres raises ProgrammingError: ERROR: relation "role" does not exist.
+
+The correct way is to delay constraints creation until all tables are
+created::
+
+    class Person(SQLObject):
+        role = ForeignKey("Role")
+
+    class Role(SQLObject):
+        person = ForeignKey("Person")
+
+    constraints = Person.createTable(applyConstraints=False)
+    constraints += Role.createTable(applyConstraints=False)
+
+    for constraint in constraints:
+        connection.query(constraint)
+
+Please be warned the delay can cause a race condition.