Question

给出以下消息表：

     Column      |            Type             |
-----------------+-----------------------------+-
 id              | integer                     |
 body            | text                        |
 conversation_id | integer                     |
 user_id         | integer                     |
 inserted_at     | timestamp without time zone |
 updated_at      | timestamp without time zone |
 sid             | character varying(255)      |
 status          | character varying(255)      |

我正在尝试在Ecto中创建以下SQL查询：

SELECT COUNT(conversation_id) FROM messages m1 WHERE m1.id = ANY(SELECT MAX(m2.id) FROM messages m2 GROUP BY m2.conversation_id) AND status = 'received';

我试过了：

query = Message
  |> where([m], m.id in fragment("ANY(select max(m2.id) from messages m2 group by m2.conversation_id)") and m.status = "received")
  |> select([m], count(m.conversation_id))

但是我遇到了运行时错误：

** (Protocol.UndefinedError) protocol Ecto.Queryable not implemented for BlackMamba.Resolver.Message, the given module is not queryable
       (ecto) lib/ecto/queryable.ex:33: Ecto.Queryable.Atom.to_query/1
       (ecto) lib/ecto/query/builder/filter.ex:46: Ecto.Query.Builder.Filter.apply/3
(black_mamba) web/resolver/conversation.ex:56: BlackMamba.Resolver.Conversation.needs_response_conversation_count/2

非常感谢任何提示。

Answer 1

我从未使用过fragment/1，但正如错误消息所示，第一个参数（您传递的参数是sql_fragment）必须是关键字列表（此列表[abc: 1, def: 2] ）你正在传递一个字符串。

Ecto清理所有原始SQL以防止SQL注入。

在Ecto中使用子查询时遇到麻烦

1 个答案: