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| -rw-r--r-- | lib/sqlalchemy/ext/automap.py | 44 |
1 files changed, 44 insertions, 0 deletions
diff --git a/lib/sqlalchemy/ext/automap.py b/lib/sqlalchemy/ext/automap.py index 17ebef5b5..a4f86c78a 100644 --- a/lib/sqlalchemy/ext/automap.py +++ b/lib/sqlalchemy/ext/automap.py @@ -387,6 +387,50 @@ SQLAlchemy can guess:: 'inherit_condition': id == Employee.id } +Handling Simple Naming Conflicts +-------------------------------- + +In the case of naming conflicts during mapping, override any of +:func:`.classname_for_table`, :func:`.name_for_scalar_relationship`, +and :func:`.name_for_collection_relationship` as needed. For example, if +automap is attempting to name a many-to-one relationship the same as an +existing column, an alternate convention can be conditionally selected. Given +a schema: + +.. sourcecode:: sql + + CREATE TABLE table_a ( + id INTEGER PRIMARY KEY + ); + + CREATE TABLE table_b ( + id INTEGER PRIMARY KEY, + table_a INTEGER, + FOREIGN KEY(table_a) REFERENCES table_a(id) + ); + +The above schema will first automap the ``table_a`` table as a class named +``table_a``; it will then automap a relationship onto the class for ``table_b`` +with the same name as this related class, e.g. ``table_a``. This +relationship name conflicts with the mapping column ``table_b.table_a``, +and will emit an error on mapping. + +We can resolve this conflict by using an underscore as follows:: + + def name_for_scalar_relationship(base, local_cls, referred_cls, constraint): + name = referred_cls.__name__.lower() + local_table = local_cls.__table__ + if name in local_table.columns: + newname = name + "_" + warnings.warn( + "Already detected name %s present. using %s" % + (name, newname)) + return newname + return name + + + Base.prepare(engine, reflect=True, + name_for_scalar_relationship=name_for_scalar_relationship) Using Automap with Explicit Declarations ======================================== |