ADO - Using ADO Streams for Binary and Text Data

The Stream object in ActiveX Data Objects (ADO) is designed to handle the reading and writing of text and binary data. Unlike the Recordset object, which primarily works with structured data stored in database tables, the Stream object manages continuous sequences of bytes or characters. This makes it ideal for working with files such as documents, images, audio, video, and text files. Developers use ADO Streams to transfer, store, and retrieve large amounts of data efficiently without manually processing individual bytes.

A Stream object can operate independently or in conjunction with other ADO objects. It provides a flexible way to manipulate data before saving it to a database or after retrieving it. For example, an application that allows users to upload profile pictures can use an ADO Stream to read the image file into memory and then store it in the database as binary data. Similarly, a document management system can retrieve files stored in a database and write them back to the file system using the same object.

Understanding Binary and Text Streams

ADO supports two types of streams:

Binary Streams

Binary streams store raw bytes rather than readable characters. They are used for non-text files such as:

  • Images (JPEG, PNG, BMP)

  • PDF documents

  • Microsoft Office files

  • Audio files

  • Video files

  • ZIP archives

Since binary data contains values that cannot be interpreted as readable text, it must be processed as bytes.

Text Streams

Text streams contain readable characters encoded in formats such as ASCII or Unicode. They are commonly used for:

  • Text documents

  • Configuration files

  • XML files

  • HTML pages

  • JSON files

  • Log files

Text streams allow developers to read and write strings while preserving character encoding.

Features of the Stream Object

The Stream object offers several useful features:

  • Reading data sequentially

  • Writing new data

  • Appending content

  • Loading data from files

  • Saving data to files

  • Supporting multiple character encodings

  • Handling binary and text formats

  • Copying data between streams

  • Moving the current reading or writing position

  • Managing large files efficiently

These capabilities make the Stream object suitable for many file handling operations within database-driven applications.

Important Properties of the Stream Object

Type

The Type property specifies whether the stream contains binary or text data.

Common values include:

  • adTypeBinary

  • adTypeText

The Type should usually be set before opening the stream.

Charset

The Charset property defines the encoding used for text streams.

Examples include:

  • UTF-8

  • Unicode

  • ASCII

  • UTF-16

Correct character encoding ensures that special symbols and multilingual text are stored accurately.

Position

The Position property indicates the current location within the stream.

Developers can:

  • Read from a specific location

  • Resume writing at a chosen position

  • Skip portions of data

Size

The Size property returns the total number of bytes or characters currently stored in the stream.

It helps determine:

  • File size

  • Amount of available data

  • Progress during file processing

EOS (End of Stream)

EOS is a Boolean property that indicates whether the current position has reached the end of the stream.

It is commonly used in loops while reading data.

Important Methods of the Stream Object

Open()

Creates and initializes the stream before any reading or writing takes place.

Close()

Releases system resources after stream operations are complete.

Closing unused streams helps prevent memory leaks.

Read()

Reads binary data from the stream.

It is mainly used with image files, documents, and other binary content.

ReadText()

Reads character data from a text stream.

Useful when processing:

  • Text files

  • XML documents

  • Configuration files

Write()

Writes binary data into the stream.

Applications use it while saving images, videos, or other binary files.

WriteText()

Writes character data into a text stream.

This method is commonly used to generate reports or log files.

LoadFromFile()

Loads an existing file directly into the stream.

Instead of manually reading every byte, the entire file becomes available within the Stream object.

SaveToFile()

Writes the stream contents to a file on disk.

This method supports:

  • Creating new files

  • Replacing existing files

SetEOS()

Marks the current position as the end of the stream.

This can remove unnecessary data beyond the specified point.

Working with Binary Large Objects (BLOBs)

A common use of ADO Streams is handling Binary Large Objects (BLOBs).

Examples include:

  • Employee photographs

  • Medical scans

  • Company logos

  • Product images

  • Video recordings

  • Digital signatures

Instead of storing files separately on the server, these objects can be stored directly inside database tables.

Typical workflow:

  1. User selects a file.

  2. The file is loaded into an ADO Stream.

  3. The stream writes the binary data into the database.

  4. When needed, the data is retrieved into another stream.

  5. The stream saves the file back to disk or displays it in the application.

This approach keeps files closely associated with database records.

Reading Text Files

ADO Streams simplify text file processing.

Typical steps include:

  1. Create the Stream object.

  2. Set the stream type to Text.

  3. Specify the character encoding.

  4. Open the stream.

  5. Load the file.

  6. Read its contents.

  7. Process the text.

  8. Close the stream.

This method supports both small and large text files.

Writing Text Files

Applications often generate output files dynamically.

Examples include:

  • Error logs

  • Sales reports

  • XML exports

  • Configuration files

  • Backup information

The Stream object allows developers to write this information directly to disk while maintaining the desired character encoding.

Reading Binary Files

Binary files require the stream type to be set to Binary.

Examples include:

  • Image files

  • PDF documents

  • Software packages

  • Multimedia files

The Read() method retrieves binary data exactly as stored without modifying its contents.

Saving Binary Files

After binary data is retrieved from a database, developers can recreate the original file by:

  • Opening a binary stream

  • Writing the retrieved bytes

  • Saving the stream to a file

This process ensures that the file remains unchanged and usable.

Advantages of Using ADO Streams

  • Supports both text and binary data.

  • Simplifies file handling operations.

  • Efficiently processes large files.

  • Preserves character encoding for text data.

  • Integrates seamlessly with other ADO objects.

  • Enables direct storage and retrieval of files from databases.

  • Reduces the need for low-level file handling code.

  • Suitable for enterprise applications that manage documents and multimedia.

Limitations

  • Performance may decrease when processing extremely large files entirely in memory.

  • Incorrect stream type settings can corrupt data.

  • Character encoding mismatches may produce unreadable text.

  • Stream objects require careful resource management to avoid memory leaks.

  • Database storage of very large files can increase database size and impact backup and restore times.

Best Practices

  • Always set the stream type before opening the stream.

  • Close the stream immediately after completing operations.

  • Use the correct character encoding for text data.

  • Validate file size before loading large files into memory.

  • Handle exceptions during file read and write operations.

  • Use binary streams for non-text files and text streams only for character data.

  • Release stream objects properly to prevent resource leaks.

  • Test file integrity after saving or retrieving binary data.

Practical Applications

The ADO Stream object is widely used in real-world applications, including:

  • Document management systems for storing and retrieving files.

  • Employee management systems for handling profile pictures and scanned documents.

  • Medical information systems for storing diagnostic images and reports.

  • Content management systems for managing multimedia assets.

  • E-commerce platforms for storing product images and downloadable files.

  • Financial applications for generating reports, invoices, and transaction logs.

  • Backup and archival systems for exporting and importing data files.

Conclusion

The ADO Stream object provides a powerful and flexible mechanism for handling both binary and text data. It extends the capabilities of ADO beyond traditional database records by enabling seamless interaction with files, multimedia content, and large objects. Whether reading configuration files, generating reports, uploading images, or managing document repositories, ADO Streams simplify data transfer while maintaining accuracy and efficiency. Proper use of stream properties, methods, and best practices ensures reliable performance and makes the Stream object an essential component for applications that combine database operations with file management.