如何在 C# 中从 PostgreSQL 中获取所选行的值? [英] How to get the value of selected row from PostgreSQL in C#?

问题描述

我正在使用带有 C# 和 Npgsql 库的 PostgreSQL 数据库.

I am using PostgreSQL database with C# and the Npgsql library.

现在我可以选择表中的最后一行，但我不知道如何为其分配 C# 变量.我知道我的选择有效，因为我之前已经成功编辑了我的最后一个条目.

Right now I can select the last row in my table, but I can not figure out how to assign a C# variable to it. I know that my selection works, because I have successfully edited my last entry before.

您可以在下面找到我的代码.请注意，我没有粘贴其余的方法，因为我认为它们无关紧要.

You can find my code below. Note that I have not pasted the rest of the methods as I think they are irrelevant.

public void myMethod()
{
    this.OpenConn(); //opens the connection

    string sql = "SELECT id FROM information_schema.tables WHERE table_schema = 'public' AND table_name = 'customers' ORDER BY id DESC, LIMIT 1";

    using (NpgsqlCommand command = new NpgsqlCommand(sql, conn))
    {
        int id = 0; //instead of '0' I want it to be equal to the ID value from the row
        //something like "int id = sqlSelection.id;" -- this obviously doesn't work

        this.CloseConn(); //close the current connection
    }
}

推荐答案

您可以通过使用特定的 DataReader 来实现此目标:

You could achieve this goal by using the specific DataReader:

public void myMethod()
{
    this.OpenConn(); //opens the connection

    string sql = "SELECT id FROM information_schema.tables WHERE table_schema = 'public' AND table_name = 'customers' ORDER BY id DESC, LIMIT 1";

    using (NpgsqlCommand command = new NpgsqlCommand(sql, conn))
    {
        int val;
        NpgsqlDataReader reader = command.ExecuteReader();
        while(reader.Read()){
           val = Int32.Parse(reader[0].ToString());
           //do whatever you like
        }

        this.CloseConn(); //close the current connection
    }
}

有用的笔记

• 在某些情况下，ExecuteScalar 是一个不错的选择
• Npgsql 文档

• In some contexts ExecuteScalar is a good alternative
• Npgsql documentation

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