--- a
+++ b/tests/generative/data_setup.py
@@ -0,0 +1,59 @@
+from ehrql.query_model.nodes import (
+    AggregateByPatient,
+    Function,
+    SelectPatientTable,
+    SelectTable,
+)
+from tests.lib.orm_utils import orm_classes_from_tables
+
+
+def setup(schema, num_patient_tables, num_event_tables):
+    patient_tables = [
+        SelectPatientTable(f"p{i}", schema=schema) for i in range(num_patient_tables)
+    ]
+    event_tables = [
+        SelectTable(f"e{i}", schema=schema) for i in range(num_event_tables)
+    ]
+    all_tables = patient_tables + event_tables
+
+    orm_classes = orm_classes_from_tables(all_tables)
+    _add_classes_to_module_namespace(orm_classes)
+
+    patient_classes = [orm_classes[table.name] for table in patient_tables]
+    event_classes = [orm_classes[table.name] for table in event_tables]
+
+    all_patients_query = _build_query(all_tables)
+
+    # We arbitrarily choose the first patient class, but all the ORM classes share the
+    # same MetaData
+    metadata = patient_classes[0].metadata
+
+    return (
+        patient_classes,
+        event_classes,
+        all_patients_query,
+        metadata,
+    )
+
+
+def _add_classes_to_module_namespace(orm_classes):
+    # It's helpful to have the classes available as module properties so that we can
+    # copy-paste failing test cases from Hypothesis. These classes naturally believe
+    # that they belong to the `orm_utils` module which created them, so we have to
+    # re-parent them here. We use only the final component of the module name as that's
+    # how we import it in `test_query_model`.
+    for class_ in orm_classes.values():
+        class_.__module__ = __name__.rpartition(".")[2]
+        globals()[class_.__name__] = class_
+
+
+def _build_query(tables):
+    clauses = [AggregateByPatient.Exists(source=table) for table in tables]
+    return _join_with_or(clauses)
+
+
+def _join_with_or(clauses):
+    query = clauses[0]
+    for clause in clauses[1:]:
+        query = Function.Or(query, clause)
+    return query