| Index: trunk/phase3/includes/filerepo/README |
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| | 2 | +Some quick notes on the file/repository architecture.
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| | 3 | +
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| | 4 | +Functionality is, as always, driven by data model.
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| | 5 | +
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| | 6 | +* The repository object stores configuration information about a file storage
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| | 7 | + method.
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| | 8 | +
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| | 9 | +* The file object is a process-local cache of information about a particular
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| | 10 | + file.
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| | 11 | +
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| | 12 | +Thus the file object is the primary public entry point for obtaining information
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| | 13 | +about files, since access via the file object can be cached, whereas access via
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| | 14 | +the repository should not be cached.
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| | 15 | +
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| | 16 | +Functions which can act on any file specified in their parameters typically find
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| | 17 | +their place either in the repository object, where reference to
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| | 18 | +repository-specific configuration is needed, or in static members of File or
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| | 19 | +FileRepo, where no such configuration is needed.
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| | 20 | +
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| | 21 | +File objects are generated by a factory function from the repository. The
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| | 22 | +repository thus has full control over the behaviour of its subsidiary file
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| | 23 | +class, since it can subclass the file class and override functionality at its
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| | 24 | +whim. Thus there is no need for the File subclass to query its parent repository
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| | 25 | +for information about repository-class-dependent behaviour -- the file subclass
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| | 26 | +is generally fully aware of the static preferences of its repository. Limited
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| | 27 | +exceptions can be made to this rule to permit sharing of functions, or perhaps
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| | 28 | +even entire classes, between repositories.
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| | 29 | +
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| | 30 | +These rules alone still do lead to some ambiguity -- it may not be clear whether
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| | 31 | +to implement some functionality in a repository function with a filename
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| | 32 | +parameter, or in the file object itself.
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| | 33 | +
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| | 34 | +So we introduce the following rule: the file subclass is smarter than the
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| | 35 | +repository subclass. The repository should in general provide a minimal API
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| | 36 | +needed to access the storage backend efficiently.
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| | 37 | +
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| | 38 | +In particular, note that I have not implemented any database access in
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| | 39 | +LocalRepo.php. LocalRepo provides only file access, and LocalFile provides
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| | 40 | +database access and higher-level functions such as cache management.
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| | 41 | +
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| | 42 | +Tim Starling, June 2007
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