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到目前为止，在 Windows 上使用 PostgreSQL 数据库时，使用 Npgsql 驱动程序而不是 ODBC 没有任何区别。但现在我找到了一个。

我有这样的代码来检查表是否存在 ODBC：

Public Function dbTableExists(ByVal dbTable As String, ByVal dbName As String) As Boolean

    Dim retval As Boolean = False
    Dim nCon As New OdbcConnection
    Dim btCommand As OdbcCommand = Nothing
    nCon.ConnectionString = "Dsn=" + dbDsn + _
                            ";database=" + dbName & _
                            ";server=" + dbServer + _
                            ";port=" + dbPort + _
                            ";uid=" + dbUser + _
                            ";pwd=" + dbPass
    Try
        nCon.Open()
        btCommand = New OdbcCommand("SELECT 1 FROM pg_tables WHERE tablename='" & dbTable + "'", nCon)
        retval = CBool(btCommand.ExecuteNonQuery())

    Catch ex As Exception
        MsgBox(ex.Message, MsgBoxStyle.Critical)
        retval = False
    End Try

    Return retval
End Function

使用此代码，如果确定的数据库中存在特定表，则我得到 True，否则得到 False。
当我尝试使用 Npgsql 而不是 ODBC 函数时非常相似：

Public Function tExists(ByVal dbTable As String, ByVal dbName As String) As Boolean

    Dim retval As Boolean = False
    Dim btCommand As NpgsqlCommand = Nothing
    Dim nCon As New NpgsqlConnection(String.Format( _
                    "Server={0};Port={1};User Id={2};Password={3};Database={4};", _
                    dbServer, dbPort, dbUser, dbPass, dbName))
    Try
        nCon.Open()
        btCommand = New NpgsqlCommand("SELECT 1 FROM pg_tables WHERE tablename='" & dbTable + "'", nCon)
        retval = CBool(btCommand.ExecuteNonQuery())

    Catch ex As Exception
        MsgBox(ex.Message, MsgBoxStyle.Critical)
        retval = False
    End Try

    Return retval
End Function

但这不会按预期工作。
无论是否存在特定表，我总是得到 True 作为结果。

知道如何让 Npgsql 函数工作吗？

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1 回答 1

2

我不知道您是否不想/不能更改您的查询，但我建议您使用该information_schema表而不是使用pg_tables. 我个人使用这种方法：

 public override bool TableExists(string tableName)
    {
        string sql = "SELECT * FROM information_schema.tables WHERE table_name = '" + tableName + "'";
        using (var con = new NpgsqlConnection(preparedConnectionString))
        {
            using (var cmd = new NpgsqlCommand(sql))
            {
                if (cmd.Connection == null)
                    cmd.Connection = con;
                if (cmd.Connection.State != ConnectionState.Open)
                    cmd.Connection.Open();

                lock (cmd)
                {
                    using (NpgsqlDataReader rdr = cmd.ExecuteReader())
                    {
                        try
                        {
                            if (rdr != null && rdr.HasRows)
                                return true;
                            return false;
                        }
                        catch (Exception)
                        {
                            return false;
                        }
                    }
                }
            }
        }
    }

（不关心注射或类似的）

于 2013-07-15T09:32:20.090 回答