Census layers (#450)

* Census layers

* Updated migration

Author: irees

schema/postgres/migrations/20250523103325_census_layers.up.pgsql

@@ -0,0 +1,27 @@
+BEGIN;
+
+ALTER TABLE tl_census_datasets rename column dataset_name to name;
+ALTER TABLE tl_census_datasets add column description text;
+ALTER TABLE tl_census_datasets alter column year_min drop not null;
+ALTER TABLE tl_census_datasets alter column year_max drop not null;
+ALTER TABLE tl_census_datasets alter column url drop not null;
+
+ALTER TABLE tl_census_sources rename column source_name to name;
+ALTER TABLE tl_census_sources add column description text;
+
+CREATE TABLE tl_census_layers (
+    id bigserial PRIMARY KEY,
+    dataset_id bigint REFERENCES tl_census_datasets(id) not null,
+    name text NOT NULL,
+    description text,
+    created_at timestamp without time zone DEFAULT now() NOT NULL,
+    updated_at timestamp without time zone DEFAULT now() NOT NULL
+);
+CREATE INDEX ON tl_census_layers (name);
+CREATE INDEX ON tl_census_layers (dataset_id);
+
+ALTER TABLE tl_census_geographies ADD COLUMN layer_id bigint REFERENCES tl_census_layers(id);
+ALTER TABLE tl_census_geographies DROP COLUMN layer_name;
+CREATE INDEX ON tl_census_geographies (layer_id);
+
+COMMIT;