Large Objects (LOBs)

Binary (BLOBs)

The SOCI library provides also an interface for basic operations on large objects (BLOBs - Binary Large OBjects).

blob b(sql); // sql is a session object
sql << "select mp3 from mymusic where id = 123", into(b);

The following functions are provided in the blob interface, mimicking the file-like operations:

The offset parameter is always counted from the beginning of the BLOB's data.

Portability notes

Long strings and XML

The SOCI library recognizes the fact that long string values are not handled portably and in some databases long string values need to be stored as a different data type. Similar concerns relate to the use of XML values, which are essentially strings at the application level, but can be stored in special database-level field types.

In order to facilitate handling of long strings and XML values the following wrapper types are defined:

struct xml_type
    std::string value;

struct long_string
    std::string value;

Values of these wrapper types can be used with into and use elements with the database target type that is specifically intended to handle XML and long strings data types.

For Oracle, these database-side types are, respectively:

For PostgreSQL, these types are:

For Firebird, there is no special XML support, but BLOB SUB_TYPE TEXT can be used for storing it, as well as long strings.

For ODBC backend, these types depend on the type of the database connected to. In particularly important special case of Microsoft SQL Server, these types are:

When using ODBC backend to connect to a PostgreSQL database, please be aware that by default PostgreSQL ODBC driver truncates all "unknown" types, such as XML, to maximal varchar type size which is just 256 bytes and so is often insufficient for XML values in practice. It is advised to set the UnknownsAsLongVarchar connection option to 1 to avoid truncating XML strings or use PostgreSQL ODBC driver 9.6.300 or later, which allows the backend to set this option to 1 automatically on connection.