feat(blog) add implementation for table meta

backend/src/model/blog/meta.sql

@@ -2,3 +2,48 @@ CREATE TABLE IF NOT EXISTS Meta
 (
     post_id UUID PRIMARY KEY
 );
+
+DROP table meta;
+
+DO
+$$
+    DECLARE
+        _post_id        UUID  := 'd5a209d4-93b1-474e-8e4e-9c78d6e6e763'; -- test data
+        _meta_cols      JSONB := '{"title": " title", "tags": "example tags", "new_col1": "new_value1", "new_col3": "new_value2"}'; -- test data
+        _exists         BOOLEAN;
+        _col_name       TEXT;
+        _col_value      TEXT;
+        _sql            TEXT;
+        _insert_columns TEXT  := 'post_id';
+        _insert_values  TEXT  := quote_literal(_post_id);
+        _update_set     TEXT  := '';
+    BEGIN
+        SELECT EXISTS(SELECT 1 FROM meta WHERE post_id = _post_id) INTO _exists;
+
+        FOR _col_name, _col_value IN SELECT key, value FROM jsonb_each_text(_meta_cols)
+            LOOP
+                IF NOT EXISTS (SELECT 1
+                               FROM information_schema.columns
+                               WHERE table_name = 'meta'
+                                 AND column_name = _col_name
+                                 -- may change in the future
+                                 AND table_schema = 'public') THEN
+                    _sql := 'ALTER TABLE meta ADD COLUMN ' || quote_ident(_col_name) || ' TEXT';
+                    EXECUTE _sql;
+                END IF;
+                _insert_columns := _insert_columns || ', ' || quote_ident(_col_name);
+                _insert_values := _insert_values || ', ' || quote_literal(_col_value);
+                _update_set := _update_set || ', ' || quote_ident(_col_name) || ' = ' || quote_literal(_col_value);
+            END LOOP;
+
+        _update_set := substring(_update_set FROM 3);
+
+        IF _exists THEN
+            _sql := 'UPDATE meta SET ' || _update_set || ' WHERE post_id = ' || quote_literal(_post_id);
+            EXECUTE _sql;
+        ELSE
+            _sql := 'INSERT INTO meta (' || _insert_columns || ') VALUES (' || _insert_values || ')';
+            EXECUTE _sql;
+        END IF;
+    END;
+$$ LANGUAGE plpgsql;