Postgres bytea column is returning string (char ar

问题:

I have been using C# to write a concrete provider implementation for our product for different databases. W/out getting into details, one of the columns is of byte array type (bytea in postgres - due to the preferences bytea was chosen over blob). The only problem, is that it does not return same value that was inserted. When I insert Int32 ("0") I get 8 [92 and 8x 48] (instead of [0,0,0,0]). I need a performance wise solution, that will return pure bytes I have inserted, instead of ASCII representation of value "0" on 8 bytes.

I am using Npgsql to retrive data. If someone knows solution for c# I will be happy to learn it as well.

Edit: Postgres 9.0, .Net 3.5

Simplification

Command query: - inside it only does an insert statment

select InsertOrUpdateEntry(:nodeId, :timeStamp, :data)

Data parameter:

byte [] value = BitConverter.GetBytes((int)someValue);

Parameter is assigned as below

command.Parameters.Add(new NpgsqlParameter("data", NpgsqlDbType.Bytea) 
{ Value = value });

Select statments:

select * from Entries

Same byte array I have entered, I want to get back. I would really appreciate your help.

Input: 0 0 0 0
Current Output: 92 48 48 48 48 48 48 48 48
Expected Output: 0 0 0 0

回答1:

In Npgsql there is NpgsqlDataReader class to retrieve inserted rows, e.g:

NpgsqlConnection conn = new NpgsqlConnection(connStr);
conn.Open();

NpgsqlCommand insertCmd =
    new NpgsqlCommand("INSERT INTO binaryData (data) VALUES(:dataParam)", conn);
NpgsqlParameter param = new NpgsqlParameter("dataParam", NpgsqlDbType.Bytea);

byte[] inputBytes = BitConverter.GetBytes((int)0);
Console.Write("Input:");
foreach (byte b in inputBytes)
    Console.Write(" {0}", b);
Console.WriteLine();

param.Value = inputBytes;
insertCmd.Parameters.Add(param);
insertCmd.ExecuteNonQuery();

NpgsqlCommand selectCmd = new NpgsqlCommand("SELECT data FROM binaryData", conn);
NpgsqlDataReader dr = selectCmd.ExecuteReader();
if(dr.Read())
{
    Console.Write("Output:");
    byte[] result = (byte[])dr[0];
    foreach(byte b in result)
        Console.Write(" {0}", b);
    Console.WriteLine();
}

conn.Close();

Result from C# app:

Input: 0 0 0 0
Output: 0 0 0 0

Result from pgAdmin:

"\000\000\000\000"

EDIT:

I found explanation why you getting:

92 48 48 48 48 48 48 48 48

I checked my code with previous version Npgsql2.0.10-bin-ms.net3.5sp1.zip and get above result (of course pgAdmin returns \000\000\000\000), so I think that best what you can do is to use another version without this bug.

ANSWER: User higher version of Npgsql than 2.0.10

回答2:

Ran the same problem, but managed to solve the problem without having to resort to changing drivers.

PHP documentation has a good description of what's happening, Postgres is returning escaped data. Check your output against an ASCII table, when you see 92 48 ... it's the text lead in to an octal escape sequence, \0xx, just like PHP describes.

Postgres's binary data type explains the output escaped octets. Fret not, there are code examples.

The solution is to tell Postgres how to bytea output is escaped, which can be either escape or hex. In this case issue the following to Postgres via psql to match your data:

ALTER DATABASE yourdb SET BYTEA_OUTPUT TO 'escape';