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Asp.net – Read a SQL-DOUBLE column as raw

I have data defined as double saved in a PSQL-Database (Actian) and I’m using DbDataReader to read the values. I know I can use GetDouble to read the value, but I would like read the raw value into a byte array. The GetBytes method comes back with InvalidCastException since it’s designed to be used with BLOB or VARBINARY. Is there any other way, like read the entire data buffer?

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  1. Chosen as BEST ANSWER
    0

    so I tested the code with SqlConnection, but unforunately the field that had the value -0 in DB came back with a 8 byte array with zeroes in MyDoubleArray. However, I tried to use basically the same code but in OleDB, which is operating on a lower level, and it worked fine. The last byte in MyDoubleArray contained a value of 128, indicating that the higest bit was set - just what I was looking for.

    using (OleDbCommand command = new OleDbCommand(sqlQuery, connection))
{
    using (OleDbDataReader reader = command.ExecuteReader())
    {
        
        while (reader.Read())
        {

             double d = (double)reader.GetDouble(0);

            byte[] MyDoubleArray = BitConverter.GetBytes(d); 

        }
     }
}

    Now I can extract the value and find a way to save it a proper way :)


  2. 0

    Hum, a somewhat strange request.

    I can see wanting a int, a long, or bigint, or even a unsigned integer value being converted to a byte array. And even perhaps a packed decimal number, which in theory is a non floating point number.

    However, I am not all that sure it makes sense to convert a IEEE floating point number to a array of 8 bytes?

    I can’t think of any software system that will be happy to consume such a floating point value.

    However, using BitConverter should work.

    I don’t have the PostgreSQL provider installed, but using SQL server, this looks to work fine for me:

            string strSQL =
            @"SELECT HotelPrice FROM tblHotelsA WHERE ID = 10";

        DataTable dt = new DataTable();

        using (SqlConnection conn= new SqlConnection(Properties.Settings.Default.MyDB))
        {
            using (SqlCommand cmdSQL = new SqlCommand(strSQL, conn))
            {
                conn.Open();
                dt.Load(cmdSQL.ExecuteReader());
            }
        }

        double myDouble = (double)dt.Rows[0]["HotelPrice"];

        byte[] MyDoubleArray = BitConverter.GetBytes(myDouble);

    The result of above is a byte array of 8 bytes long.

    So, replace the SQL provider with the PostgreSQL provider, and the posted code should work fine for your needs.

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