Using Caché Objects - InterSystems Documentation

Streams
Stream data may be stored in either an external file or a Caché global, depending on how the
stream property is defined. The %FileCharacterStream and %FileBinaryStream classes are
used for streams stored as external files, while %GlobalCharacterStream and
%GlobalBinaryStream are used for streams stored as globals. All four classes can use the
optional LOCATION parameter to specify a default storage location.
In the following example, the JournalEntry class contains four stream properties (one for each
of the four basic stream classes), and specifies a default storage location for two of them:
Class testPkg.JournalEntry Extends %Persistent
{
Property DailyText As %FileCharacterStream;
Property DailyImage As %FileBinaryStream(LOCATION = "C:/Images");
Property Text As %GlobalCharacterStream(LOCATION = "^MyText");
Property Picture As %GlobalBinaryStream;
}
In this example, data for DailyImage will be stored in a file (with an automatically generated
name) in the C:/Images directory, while the data for the Text property will be stored in a global
named ^MyText.
15.1.1 Projecting Streams to ODBC
Streams are projected to ODBC as BLOBs. Their ODBC type is LONG VARCHAR (or
LONG VARBINARY). The ODBC driver/server uses a special protocol to read/write BLOBs.
Typically you have to write BLOB applications by hand, since the standard reporting tools
do not support them.
15.2 Using the Stream Interface
All streams inherit a set of methods and properties used to manipulate the data they contain.
Some commonly used methods include the following:
• Read — Read a specified number of characters starting at the current position in the
stream.
• Write — Append data to the stream, starting at the current position. Overwrites existing
data if the position is not set to the end of the stream.
• Rewind — Move to the beginning of the stream.
• MoveTo — Move to a given position in the stream.
• MoveToEnd — Move to the end of the stream.
134 Using Caché Objects