如何在c#中返回postgresql函数的结果?控制台输出为空 [英] How to return the result of a postgresql function in c#? Console output empty

问题描述

我有一个问题，我在 postgresql 中有一个计算两个整数的函数，应该将结果返回到 c# (npgsql) 控制台，我不知道我的错误在哪里，因为调试器没有对我这有帮助.

I have the problem that i have a function in postgresql that calculates two integer and should return the result to the c# (npgsql) conosle and i don't know where my mistake is, because the debugger doesn't say anything to me which is helpful.

所以首先是 c# 和函数的代码.

so first of all the code of c# and of the function.

                ...
            cmd.Parameters["x"].Value = 20;
            cmd.Parameters["y"].Value = 22;
            connection.Open();

            if (connection.State == System.Data.ConnectionState.Open) {
                //Console.WriteLine(cmd.Parameters["x"].Value);
                command.ExecuteNonQuery();
                Console.WriteLine(cmd.Parameters["sum"].Value);

            }

现在是数据库的代码:

CREATE OR REPLACE FUNCTION t2(
    IN x integer,
    IN y integer,
    OUT sum integer)
  RETURNS integer AS
$BODY$BEGIN
    sum := x + y;
    INSERT INTO  t2 (x, y, sum) values (x, y, sum);
END

所以当我尝试运行它时，

So when i try to run it,

Console.WriteLine(cmd.Parameters["sum"].Value);

将为空且 ["sum"].Value 为 NULL.我究竟做错了什么?我说的对，当我说sum"是一个 OUT 变量时，我不需要返回?

will be empty and the ["sum"].Value is NULL. What am I doing wrong? Am I right, that when I say that "sum" is an OUT variable, I do not need a return?

请帮忙.

解决了，谢谢大家！@Patrick 给了我正确的答案:使用 ExecuteScalar() 而不是 ExecuteNonQuery()

SOLVED, thank you to all! @Patrick gave me the right answer: use ExecuteScalar() instead of ExecuteNonQuery()

推荐答案

代替

command.ExecuteNonQuery();

你应该打电话

Object res = command.ExecuteScalar();
Console.WriteLine(res);

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