diff options
Diffstat (limited to 'lib/sqlalchemy/dialects')
| -rw-r--r-- | lib/sqlalchemy/dialects/mysql/base.py | 41 |
1 files changed, 40 insertions, 1 deletions
diff --git a/lib/sqlalchemy/dialects/mysql/base.py b/lib/sqlalchemy/dialects/mysql/base.py index d0f654fe2..445355e9f 100644 --- a/lib/sqlalchemy/dialects/mysql/base.py +++ b/lib/sqlalchemy/dialects/mysql/base.py @@ -265,6 +265,41 @@ http://dev.mysql.com/doc/refman/5.0/en/create-index.html http://dev.mysql.com/doc/refman/5.0/en/create-table.html +.. _mysql_foreign_keys: + +MySQL Foreign Key Options +------------------------- + +MySQL does not support the foreign key arguments "DEFERRABLE", "INITIALLY", +or "MATCH". Using the ``deferrable`` or ``initially`` keyword argument with +:class:`.ForeignKeyConstraint` or :class:`.ForeignKey` will have the effect of these keywords being +rendered in a DDL expression, which will then raise an error on MySQL. +In order to use these keywords on a foreign key while having them ignored +on a MySQL backend, use a custom compile rule:: + + from sqlalchemy.ext.compiler import compiles + from sqlalchemy.schema import ForeignKeyConstraint + + @compiles(ForeignKeyConstraint, "mysql") + def process(element, compiler, **kw): + element.deferrable = element.initially = None + return compiler.visit_foreign_key_constraint(element, **kw) + +.. versionchanged:: 0.9.0 - the MySQL backend no longer silently ignores + the ``deferrable`` or ``initially`` keyword arguments of :class:`.ForeignKeyConstraint` + and :class:`.ForeignKey`. + +The "MATCH" keyword is in fact more insidious, and is explicitly disallowed +by SQLAlchemy in conjunction with the MySQL backend. This argument is silently +ignored by MySQL, but in addition has the effect of ON UPDATE and ON DELETE options +also being ignored by the backend. Therefore MATCH should never be used with the +MySQL backend; as is the case with DEFERRABLE and INITIALLY, custom compilation +rules can be used to correct a MySQL ForeignKeyConstraint at DDL definition time. + +.. versionadded:: 0.9.0 - the MySQL backend will raise a :class:`.CompileError` + when the ``match`` keyword is used with :class:`.ForeignKeyConstraint` + or :class:`.ForeignKey`. + """ import datetime @@ -1612,7 +1647,11 @@ class MySQLDDLCompiler(compiler.DDLCompiler): (self.preparer.format_table(constraint.table), qual, const) - def define_constraint_deferrability(self, constraint): + def define_constraint_match(self, constraint): + if constraint.match is not None: + raise exc.CompileError( + "MySQL ignores the 'MATCH' keyword while at the same time " + "causes ON UPDATE/ON DELETE clauses to be ignored.") return "" class MySQLTypeCompiler(compiler.GenericTypeCompiler): |