如何使用pqxx的hstore

Question

我有一个PostgreSQL表定义如下：

                    Table "public.dm_metadata"
   Column   |            Type             |       Modifiers        
------------+-----------------------------+------------------------
 id         | character varying(60)       | not null
 insertedat | timestamp without time zone | not null default now()
 metadata   | hstore                      | 
Indexes:
    "dm_metadata_pkey" PRIMARY KEY, btree (id, insertedat)
    "dm_metadata_metadata_idx" gist (metadata)

有人能举例说明如何使用libpqxx和预编译语句将INSERT和SELECT数据插入此表吗？

具体来说，我对以下查询感兴趣：

INSERT INTO dm_metadata(id, metadata) VALUES ('werwer', '"a" => 1234');
INSERT INTO dm_metadata(id, metadata) VALUES ('werwer', '"a" => 1234, "b" => "hello"');
SELECT metadata FROM dm_metadata WHERE metadata @> '"a"=>1234';
SELECT metadata FROM dm_metadata WHERE metadata @> '"a"=>1234,"b"=>"hello"';