Verify string lengths when creating model objects

pyjeeves/models/ext.py

@@ -0,0 +1,55 @@
+from sqlalchemy.ext.instrumentation import InstrumentationManager
+# from sqlalchemy.orm.interfaces import AttributeExtension
+from sqlalchemy.orm import ColumnProperty
+from sqlalchemy.types import String
+from sqlalchemy import event
+
+
+class Error(Exception):
+    """Base class for exceptions in this module."""
+    pass
+
+
+class ValidationError(Error):
+    pass
+
+
+class JeevesDBError(Error):
+    """Exception raised for errors in the input.
+
+    Attributes:
+        expression -- input expression in which the error occurred
+        message -- explanation of the error
+    """
+
+    def __init__(self, field, message):
+        super().__init__(message)
+        self.field = field
+        self.message = message
+
+
+class InstallValidatorListeners(InstrumentationManager):
+    def post_configure_attribute(self, class_, key, inst):
+        """Add validators for any attributes that can be validated."""
+        prop = inst.prop
+        # Only interested in simple columns, not relations
+        if isinstance(prop, ColumnProperty) and len(prop.columns) == 1:
+            col = prop.columns[0]
+            # if we have string column with a length, create a length validator listner
+            if isinstance(col.type, String) and col.type.length:
+                event.listen(
+                    getattr(class_, key), 'set', LengthValidator(
+                        col.name, col.type.length), retval=True)
+
+
+class LengthValidator():
+    def __init__(self, col_name, max_length):
+        self.col_name = col_name
+        self.max_length = max_length
+
+    def __call__(self, state, value, oldvalue, initiator):
+        if len(value) > self.max_length:
+            raise ValidationError(
+                "%s.%s: Length %d exceeds allowed %d" % (
+                    state.__class__.__name__, self.col_name, len(value), self.max_length))
+        return value