Merge "create placeholder tables for non-reflected remotes" into main

Author: zzzeek

alembic/autogenerate/compare/constraints.py

@@ -580,6 +580,44 @@ def _make_foreign_key(
         initially=options.get("initially"),
         name=params["name"],
     )
+
+    referred_schema = params["referred_schema"]
+    referred_table = params["referred_table"]
+
+    remote_table_key = sqla_compat._get_table_key(
+        referred_table, referred_schema
+    )
+    if remote_table_key not in conn_table.metadata:
+        # create a placeholder table
+        sa_schema.Table(
+            referred_table,
+            conn_table.metadata,
+            schema=(
+                referred_schema
+                if referred_schema is not None
+                else sa_schema.BLANK_SCHEMA
+            ),
+            *[
+                sa_schema.Column(remote, conn_table.c[local].type)
+                for local, remote in zip(
+                    params["constrained_columns"], params["referred_columns"]
+                )
+            ],
+            info={"alembic_placeholder": True},
+        )
+    elif conn_table.metadata.tables[remote_table_key].info.get(
+        "alembic_placeholder"
+    ):
+        # table exists and is a placeholder; ensure needed columns are present
+        placeholder_table = conn_table.metadata.tables[remote_table_key]
+        for local, remote in zip(
+            params["constrained_columns"], params["referred_columns"]
+        ):
+            if remote not in placeholder_table.c:
+                placeholder_table.append_column(
+                    sa_schema.Column(remote, conn_table.c[local].type)
+                )
+
     # needed by 0.7
     conn_table.append_constraint(const)
     return const
@@ -595,6 +633,7 @@ def _compare_foreign_keys(
 ) -> PriorityDispatchResult:
     # if we're doing CREATE TABLE, all FKs are created
     # inline within the table def
+
     if conn_table is None or metadata_table is None:
         return PriorityDispatchResult.CONTINUE
 

alembic/util/sqla_compat.py

@@ -293,6 +293,13 @@ def _get_variant_mapping(type_):
         return type_.impl, type_.mapping
 
 
+def _get_table_key(name: str, schema: Optional[str]) -> str:
+    if schema is None:
+        return name
+    else:
+        return schema + "." + name
+
+
 def _fk_spec(constraint: ForeignKeyConstraint) -> Any:
     if TYPE_CHECKING:
         assert constraint.columns is not None

docs/build/unreleased/1787.rst

@@ -0,0 +1,27 @@
+.. change::
+    :tags: bug, autogenerate
+    :tickets: 1787
+
+    Fixed regression in version 1.18.0 due to :ticket:`1771` where autogenerate
+    would raise ``NoReferencedTableError`` when a foreign key constraint
+    referenced a table that was not part of the initial table load, including
+    tables filtered out by the
+    :paramref:`.EnvironmentContext.configure.include_name` callable or tables
+    in remote schemas that were not included in the initial reflection run.
+
+    The change in :ticket:`1771` was a performance optimization that eliminated
+    additional reflection queries for tables that were only referenced by
+    foreign keys but not explicitly included in the main reflection run.
+    However, this optimization inadvertently removed the creation of
+    :class:`.Table` objects for these referenced tables, causing autogenerate
+    to fail when processing foreign key constraints that pointed to them.
+
+    The fix creates placeholder :class:`.Table` objects for foreign key targets
+    that are not reflected, allowing the autogenerate comparison to proceed
+    without error while maintaining the performance improvement from
+    :ticket:`1771`. When multiple foreign keys reference different columns in
+    the same filtered table, the placeholder table accumulates all necessary
+    columns. These placeholder tables may be visible when using the
+    :paramref:`.EnvironmentContext.configure.include_object` callable to
+    inspect :class:`.ForeignKeyConstraint` objects; they will have the name,
+    schema and basic column information for the relevant columns present.