Question

我在Ubuntu上使用.NET Npgsql库连接到PostgreSQL dbms。

在我的数据库中，我有一个声明的FUNCTION“user_plan（）”，它返回一个SETOF SELECT查询结果：

CREATE FUNCTION user_plan(varchar(20), int) RETURNS SETOF user_plan_type AS
$$
    SELECT pr.participant, t.talk_id, t.start_time, t.description, t.room
    FROM talks t JOIN participant_registrations pr USING(event)
    WHERE pr.participant=$1
    ORDER BY 3
    LIMIT $2;
$$ LANGUAGE SQL;

当我直接从psql环境测试时，一切都按预期进行。但是当我使用Npgsql库以这种方式调用FUNCTION时：

using (var query = new NpgsqlCommand())
{
    query.Connection = conn;
    query.CommandText = "SELECT user_plan(@user, @limit::int)";
    query.Parameters.AddWithValue("user", login);
    query.Parameters.AddWithValue("limit", limit);
    using (var dr = query.ExecuteReader()) {
        while(dr.Read()){
            Console.Write("{0} \n", dr[0]);
        }
    }
}

或者这样：

using (var query = new NpgsqlCommand())
{
    query.Connection = conn;
    query.CommandText = "SELECT user_plan(@user, @limit::int)";
    query.Parameters.AddWithValue("user", login);
    query.Parameters.AddWithValue("limit", limit);
    using (var dr = query.ExecuteReader()) {
        while(dr.Read()){
            Console.WriteLine(dr.GetString(0));
        }
    }
}

我收到以下错误：

System.Collections.ListDictionaryInternal: 
The field 'user_plan' has a type currently unknown to Npgsql (OID 16642).
You can retrieve it as a string by marking it as unknown, please see the FAQ.

我只是想编写控制user_plan()查询的结果集。我该怎么办？

Answer 1

问题出在query本身。它返回函数类型，而不是返回值。

而不是：

query.CommandText = "SELECT user_plan(@user, @limit::int)";

应该是：

query.CommandText = "SELECT * FROM user_plan(@user, @limit::int)";

在Ubuntu上使用.NET的Npgsql：如何将数据库查询结果写入控制台？

1 个答案: