File system properties

A property is a named, persistent instance attached to a file system entity. The file system uses properties to store a heterogenous collection of instances associated with a specific file entity. All file entities (classes that derive from TFileSystemEntity) can access properties because TFileSystemEntity uses MPropertyStore as a mixin class.

NOTE ZW You can retrieve and modify values for the properties that the file system predefines. In future releases, you will be able to define additional properties of your own and maintain those.

Types of information that properties store for a file system entity include:

Name
Creation date and time
Modification date and time
Size
Type of entity

A specific file system entity can also manage the storage of properties that only apply to that entity type. For example, TFile instances manage end-of-file information stored as a property, as well as managing the storage of the file name, creation date, modification date, file size, and entity type (which is always file in this case).

NOTE The file contents are not properties--you can only access the file contents using TFileStream or TMappedFile. See "Accessing file system properties" on page 59 for details.

The file system provides property services to:

Retrieve and store properties singly or in batches
Filter volume and directory iterations using queries
Accelerate queries using secondary indices
Retrieve meta data, such as how many properties an entity has, or how big the properties are

Individual file system entities inherit the member functions to handle these procedures from TFileSystemEntity.

To access the individual properties of a file system entity, such as the name or modification date, you do not need to know about the property classes. The specific member functions that you need to work with the file system properties are already part of the file system entity classes.

If you want to perform batched property operations, construct property queries, or create new properties, you then need to understand more about how the property classes work. For more information about properties, see Chapter 5, "Properties" in Foundation Services.

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