Refine catalog migration for Postgres (#543)

* Refine migration for postgres.

* Use begin()

* one migration again

tiled/catalog/migrations/versions/83889e049ddc_reorganize_structure_and_rename_.py → tiled/catalog/migrations/versions/83889e049ddc_add_table_to_structurefamily_enum.py

@@ -13,6 +13,7 @@
 from sqlalchemy.dialects.postgresql import JSONB
 
 from tiled.serialization.table import deserialize_arrow
+from tiled.structures.core import StructureFamily
 from tiled.structures.table import B64_ENCODED_PREFIX
 
 # revision identifiers, used by Alembic.
@@ -21,26 +22,34 @@
 branch_labels = None
 depends_on = None
 
+
 # Use JSON with SQLite and JSONB with PostgreSQL.
 JSONVariant = sa.JSON().with_variant(JSONB(), "postgresql")
 
-# This is a *data migration* only. There are no changes to the SQL schema.
-
 
 def upgrade():
     connection = op.get_bind()
 
+    if connection.engine.dialect.name == "postgresql":
+        # This change must be committed befor ethe new 'table' enum value can be used.
+        with op.get_context().autocommit_block():
+            op.execute(
+                sa.text(
+                    "ALTER TYPE structurefamily ADD VALUE IF NOT EXISTS 'table' AFTER 'dataframe'"
+                )
+            )
     # Rename "dataframe" to "table".
     nodes = sa.Table(
         "nodes",
         sa.MetaData(),
         sa.Column("id", sa.Integer),
         sa.Column("structure_family", sa.Unicode(32)),
     )
-    connection.execute(
-        nodes.update()
-        .where(nodes.c.structure_family == "dataframe")
-        .values(structure_family="table")
+    # Use a raw text query to work around type fussiness in postgres.
+    op.execute(
+        sa.text(
+            "UPDATE nodes SET structure_family='table' WHERE nodes.structure_family = 'dataframe'"
+        )
     )
 
     data_sources = sa.Table(
@@ -59,15 +68,15 @@ def upgrade():
         ).select_from(joined)
     ).fetchall()
     for id_, structure, structure_family in results:
-        if structure_family == "array":
+        if structure_family == StructureFamily.array:
             # Consolidate "macro" and "micro".
             new_structure = {}
             new_structure["shape"] = structure["macro"]["shape"]
             new_structure["dims"] = structure["macro"]["dims"]
             new_structure["chunks"] = structure["macro"]["chunks"]
             new_structure["resizable"] = structure["macro"]["resizable"]
             new_structure["data_type"] = structure["micro"]
-        elif structure_family == "table":
+        elif structure_family == StructureFamily.table:
             # Consolidate "macro" and "micro".
             new_structure = {}
             new_structure["columns"] = structure["macro"]["columns"]