Astronomer - Apache Airflow 3 Fundamentals DAG Authoring Study Guide

6: Passing data and templating - XComs, Jinja, Params, Variables, Connections

This chapter connects the DAG topology built in earlier chapters to a working data-passing and templating surface. It covers return-value XComs, explicit `ti.xcom_push` and `ti.xcom_pull` with `task_ids`, `key`, and `map_indexes`; `multiple_outputs`, `XComArg.map`, and `XComArg.zip`; custom XCom backends and the metadata-database size limitation of the default backend; the full Jinja runtime context, `template_fields`, `template_ext`, `render_template_as_native_obj`, `user_defined_macros`, `user_defined_filters`, and `template_searchpath`; DAG-level `params` with JSON-schema validation and the trigger-form UI; and Variable and Connection access with a firm rule against top-level metadata-database reads.