如何在PostgreSQL plpgsql函数中将JSON文本字段强制转换为UUID

我在RPC(远程过程调用)中使用了以下函数,在该函数中,我尝试访问JSON对象的可选文本字段,并将其强制转换为UUID:

CREATE OR REPLACE FUNCTION update_wcomponent (item wcomponents)
returns wcomponents
language plpgsql
security definer
SET search_path = public
as $$
DECLARE
  existing wcomponents%ROWTYPE;
BEGIN

  UPDATE wcomponents
  SET
    modified_at = now(),
    title = item.json::json->'title',
    type = item.json::json->'type',
    -- Following line errors
    attribute_id = (item.json::json->'attribute_wcomponent_id')::text::uuid,
    json = item.json
  WHERE id = item.id AND modified_at = item.modified_at;

  -- Get the latest value
  SELECT * INTO existing FROM wcomponents WHERE id = item.id;

  return existing;
END;
$$;

但是,将文本强制转换为uuid时会出现以下错误:

invalid input syntax for type uuid: ""310edbfb-0af1-411b-9275-3fc87948c3a5""

我在这里发布了一个JSON对象,其结构如下:

{
    "item": {
        "base_id": 18,
        "id": "27e46ec1-3d9a-412d-9807-8e08e515988d",
        "json": {
            "id": "27e46ec1-3d9a-412d-9807-8e08e515988d",
            "title": "",
            "type": "state_value",
            "attribute_wcomponent_id": "310edbfb-0af1-411b-9275-3fc87948c3a5"
        },
        "modified_at": "2022-04-23T22:11:13.533Z"
    }
}

attribute_wcomponent_id 是可选的,所以当 undefined 因为它将缺席。

如何成功地将它从json文本属性转换为uuid?文本字符串似乎被引用为 "310edbfb-0af1-411b-9275-3fc87948c3a5" 而不仅仅是 310edbfb-0af1-411b-9275-3fc87948c3a5 .