postgresql C# 连接到 postgres 数据库
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C# connecting to a postgres database
提问by robertpas
This is my first time connecting to a database, but i'm having some problems
这是我第一次连接到数据库，但我遇到了一些问题
using Npgsql;
namespace DBPrj
{
class Program
{
static void Main(string[] args)
{
bool boolfound=false;
NpgsqlConnection conn = new NpgsqlConnection("Server=<ip>; Port=5432; User Id=Admin; Password=postgres.1; Database=Test1"); //<ip> is an actual ip address
conn.Open();
NpgsqlCommand cmd = new NpgsqlCommand();
NpgsqlDataReader dr= cmd.ExecuteReader(); //I get InvalidOperationException : The connection is not open.
if (dr.Read())
{
boolfound=true;
Console.WriteLine("connection established");
}
if(boolfound==false)
{
Console.WriteLine("Data does not exist");
}
dr.Close();
conn.Close();
}
}
}
}
What could be the problem? Is the NpgsqlConnection string written correctly? Could the database be protected from remote access?
可能是什么问题呢？NpgsqlConnection 字符串是否正确写入？可以保护数据库免受远程访问吗？
How could I fix this problem?
我该如何解决这个问题？
Thanks in advance!
提前致谢！
回答by Karl-Johan Sj?gren
You never assign your NpgsqlConnectionto your NpgsqlCommandand you don't supply a query to execute for your NpgsqlDataReader, fixing that should solve the immediate problems.
您永远不会将您的分配NpgsqlConnection给您NpgsqlCommand，也不会为您的 提供查询来执行NpgsqlDataReader，修复应该可以解决眼前的问题。
Also, wrapping at least your NpgsqlConnectionin a using()-statement is a good idea to make sure that the connection is always closed, even if there is an exception.
此外，至少NpgsqlConnection在 -using()语句中包装您是一个好主意，以确保连接始终关闭，即使有异常也是如此。
using Npgsql;
namespace DBPrj
{
class Program
{
static void Main(string[] args)
{
bool boolfound=false;
using(NpgsqlConnection conn = new NpgsqlConnection("Server=<ip>; Port=5432; User Id=Admin; Password=postgres.1; Database=Test1"))
{
conn.Open();
NpgsqlCommand cmd = new NpgsqlCommand("SELECT * FROM Table1", conn);
NpgsqlDataReader dr= cmd.ExecuteReader();
if (dr.Read())
{
boolfound=true;
Console.WriteLine("connection established");
}
if(boolfound==false)
{
Console.WriteLine("Data does not exist");
}
dr.Close();
}
}
}
}
回答by Shane.C
In your connection string you may be missing a semi-colon at the end of database.
在您的连接字符串中，您可能在数据库末尾缺少分号。
Database=Test1"
may need to be;
可能需要；
Database=Test1;"
also - it may be worth wrapping your conn.open() in a try catch statement for user-friendliness and ease of catching errors.
此外 - 为了用户友好和易于捕捉错误，将 conn.open() 包装在 try catch 语句中可能是值得的。
Edit 1:
编辑1：
Just did a little reading. Does NpgsqlCommand need parameters to be passed to it? just in pseudo code, something like;
刚读了一点。NpgsqlCommand 需要传递参数吗？只是在伪代码中，例如；
NpgsqlCommand cmd = new NpgsqlCommand(query, conn);
