Question

我正在使用NpgSQL和PostgreSQL以及ADO.NET。原谅这个问题的简单性，因为我本周刚开始使用PostgreSQL和NpgSQL。

这样的事情很好：

[Test]
public void InsertNoParameters()
{
    NpgsqlConnection conn = new NpgsqlConnection("Host=localhost; Database=postgres; User ID=postgres; Password=password");
    conn.Open();

    IDbCommand command = conn.CreateCommand();
    string sql = "INSERT INTO Customers (FirstName,LastName) VALUES ('Test','Tube')";
    command.CommandText = sql;
    command.ExecuteNonQuery();
    conn.Close();
}

当我输入参数时，我收到错误消息： Npgsql.NpgsqlException：错误：42703：列“_firstname”不存在

[Test]
public void InsertWithParameters()
{
NpgsqlConnection conn = new NpgsqlConnection("Host=localhost; Database=postgres; User ID=postgres; Password=password");
conn.Open();

IDbCommand command = conn.CreateCommand();
string sql = "INSERT INTO Customers (FirstName,LastName) VALUES (_FirstName,_LastName)";
command.CommandText = sql;

var parameter = command.CreateParameter();
parameter.ParameterName = "_FirstName";
parameter.Value = "Test";
command.Parameters.Add(parameter);

parameter = command.CreateParameter();
parameter.ParameterName = "_LastName";
parameter.Value = "Tube";
command.Parameters.Add(parameter);

command.ExecuteNonQuery();
conn.Close();
}

Answer 1

评论中的回答是正确的：

Npgsql不支持_作为参数占位符表示法。您应该使用@或:(所以@FirstName或：FirstName，而不是_FirstName）。
PostgreSQL会自动小写你的表名和列名，除非它们是双引号。在SQL查询中使用小写名称（更简单）或引用标识符。

所以你的代码应该或多或少看起来像这样：

namespace SomethingLikeStrategy
{
  public interface Behaviour {
    void doThis();
    void changeM(ref int m);
    void doThat();
  }

  public class BehaviourOriginal : Behaviour {
    public void doThis() {
      Console.WriteLine("foo");
    }
    public void changeM(ref int m) {
      m = 20;
    }
    public void doThat() {
      throw new Exception("not implemented");
    }
  }

  public class BehaviourSpecial : Behaviour {
    public void doThis() {
      Console.WriteLine("bar");
    }
    public void changeM(ref int m) {
      m = 10;
    }
    public void doThat() {
      throw new Exception("not implemented");
    }
  }

  public class MyClass {

    Behaviour mBehaviour;
    int mM = 0;

    public MyClass() {
      mBehaviour = new BehaviourOriginal();
    }

    public void setSpecialBehaviour(bool special) {
      if (special) {
        mBehaviour = new BehaviourSpecial();
      } else {
        mBehaviour = new BehaviourOriginal();
      }
    }

    public void doThis() {
      mBehaviour.doThis();
    }

    public void doThat() {
      mBehaviour.doThat();
    }

    public void changeM() {
      mBehaviour.changeM(ref mM);
    }

    public void printM() {
      Console.WriteLine(mM);
    }

  }

  class Program
  {
    public static void Main(string[] args)
    {
      MyClass myClass = new MyClass();
      myClass.doThis();
      myClass.setSpecialBehaviour(true);
      myClass.doThis();

      myClass.setSpecialBehaviour(false);
      myClass.printM();
      myClass.changeM();
      myClass.printM();
      myClass.setSpecialBehaviour(true);
      myClass.changeM();
      myClass.printM();

      Console.Write("Press any key to continue . . . ");
      Console.ReadKey(true);
    }
  }
}

使用ADO.NET进行PostgreSQL参数化插入

1 个答案: