Postgresql – How to insert binary data into a PostgreSQL BYTEA column using libpqxx

postgresqlpostgresql-9.1

I'm a newbie at SQL, and even greener when it comes to using the PostgreSQL C++ API libpqxx.

What I'd like to do is insert some binary data into a BYTEA column, but I find the Doxygen output is lacking in details. The fact that http://pqxx.org/ has been down for the past few days isn't helping me…

How would I go about inserting the contents of somefile.bin into a table with a BYTEA column?

What I have is along these lines:

pqxx::work work( conn );
work.exec( "CREATE TABLE test ( name varchar(20), data BYTEA )" );
work.exec( "INSERT INTO test( name, data ) VALUES ( 'foo', <insert filename.bin here> )" );
work.commit();

If it makes a difference, I'd like to use the new hex format for BYTEA available in PostgreSQL 9.1.

Best Answer

Took a while, but I figured out how to do it. Here is some example code:

pqxx::connection conn( ... );
conn.prepare( "test", "INSERT INTO mytable( name, binfile ) VALUES ($1, $2)" );
pqxx::work work( conn );
for ( ... )
{
    std::string name = "foo";
    void * bin_data = ...; // -- obviously do what you need to get the binary data...
    size_t bin_size = 123; // -- ...and the size of the binary data

    pqxx::binarystring blob( bin_data, bin_size );
    pqxx::result r = work.prepared( "test" )( name )( blob ).exec();
}
work.commit();

Related Solutions

Postgresql – How to insert (file) data into a PostgreSQL bytea column

as superuser:

create or replace function bytea_import(p_path text, p_result out bytea) 
                   language plpgsql as $$
declare
  l_oid oid;
begin
  select lo_import(p_path) into l_oid;
  select lo_get(l_oid) INTO p_result;
  perform lo_unlink(l_oid);
end;$$;

lo_get was introduced in 9.4 so for older versions you would need:

create or replace function bytea_import(p_path text, p_result out bytea) 
                   language plpgsql as $$
declare
  l_oid oid;
  r record;
begin
  p_result := '';
  select lo_import(p_path) into l_oid;
  for r in ( select data 
             from pg_largeobject 
             where loid = l_oid 
             order by pageno ) loop
    p_result = p_result || r.data;
  end loop;
  perform lo_unlink(l_oid);
end;$$;

then:

insert into my_table(bytea_data) select bytea_import('/my/file.name');

Postgresql – How to select bytea data as binary data, inserted as hex-encoded from binary

You're not going to get binary data out of psql and SELECT. psql will format it for readability. You could try something with lo_export similar to the answer in How to insert (file) data into a PostgreSQL bytea column to get the data written to a file.

However, most PostgreSQL client adapters (perl DBI, Ruby 'pg', etc) can give you the data in binary when you SELECT bytea columns. Just write a little program using an appropriate adapter in the language of your choice.

Best Answer

Related Solutions

Postgresql – How to insert (file) data into a PostgreSQL bytea column

Postgresql – How to select bytea data as binary data, inserted as hex-encoded from binary

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