disallow that structures or properties are related to themselves

Author: ScriptRaccoon

databases/catdat/schema/001_structures.sql

@@ -27,6 +27,7 @@ CREATE TABLE related_structures (
     structure_id TEXT NOT NULL,
     related_structure_id TEXT NOT NULL,
     type TEXT NOT NULL,
+    CHECK (structure_id != related_structure_id),
     PRIMARY KEY (structure_id, related_structure_id),
     FOREIGN KEY (structure_id, type) REFERENCES structures (id, type) ON DELETE CASCADE,
     FOREIGN KEY (related_structure_id, type) REFERENCES structures (id, type) ON DELETE CASCADE

databases/catdat/schema/002_properties.sql

@@ -24,6 +24,7 @@ CREATE TABLE related_properties (
     property_id TEXT NOT NULL,
     related_property_id TEXT NOT NULL,
     type TEXT NOT NULL,
+    CHECK (property_id != related_property_id),
     PRIMARY KEY (property_id, related_property_id),
     FOREIGN KEY (property_id, type)
         REFERENCES properties (id, type) ON DELETE CASCADE,