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Related Facilities

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The XFormDBF application is built upon and integrated with a number of general purpose components of SpaceTime Systems' VFPUtils library.  Here is a brief summary of these related generic modules:

Commander
A general purpose facility for dynamically defining and executing table-driven pseudo-functions, based on a meta-file of function definitions.  This is actually an underlying component of the Saver mechanism.  Form configurations are saved by generating a Commander-based function definition, whose later execution is used to restore the previous state.

ErrHandler
Classes and functions for support of VFP error-handling features.  The main form is derived from the generic ErrHForm class, which gives it a number of "ehp_" properties and "ehm_" methods.  This mechanism is used to support a way of returning detailed error information, as well as providing extensive error detection, reporting, and diagnostic capabilities.

Saver
A class library and accompanying dialog forms for supporting state-saving and restoration features, which are covered by the Config Page.  When a form's state  or "configuration" is saved, a Commander-based state-restoration function is generated and stored in a "meta-file".  The execution of a such a state restoration function returns an object to its previous state.  An unlimited number of different configurations can be stored in one or more meta-files.  A configuration consists of all the user-settable parameters of an object, e.g. window sizing and placement, but not including the contents of external files or tables that may be referenced by the object's properties.

SplitCon
A general purpose class library for supporting split containers and splitter bars.  This is used in both Saver's Switch To... dialog and the Fields page of XFormDBF.

Assorted Utility Functions

In addition to the preceding subsystems, the following self-contained utility functions are useful to XFormDBF:

cmdprg.prg
generic UDF to generate/compile/run/cleanup a PRG.  XFormDBF uses this for optimization of its runtime processing logic, unless you select the Don't Optimize option.
cmdrclon.prg
a Commander-related utility UDF for cloning meta-file based function definitions.  Since XFormDBF's saved configurations are represented as Commander functions, this utility can be used to clone template configurations from a separate meta-file reserved specifically for this purpose.
denull.prg
generic UDF to remove all NULL values from a given table.  This may be useful for pre-processing of input files before invoking XFormDBF.  Otherwise, you may have to complicate mappings in order to handle NULL values without errors.  Note that outer joins in SQL queries can introduce NULLs even though none of the underlying tables support them.  Use of denull.prg can greatly simplify such problems and speed up processing.
docmd.prg
generic UDF to execute multiple VFP command lines in a single step.  This is a handy way to create tiny VFP "programs" without having to create a true .PRG and compile it into an .FXP file.  In XFormDBF, this can be used to construct simple initialization and cleanup expressions, for example.
getx.prg
generic UDF wrapper for VFP's GETEXPR command.  Used by XFormDBF to obtain a new mapping expression when you double-click on an entry in the list of output field mappings.  (Note that this function does not eliminate VFP's spurious validation errors when an expression contains a UDF.)
ifcmd.prg
generic UDF for conditional execution of VFP command lines.  This is similar to the docmd() function, but it adds support of a simple IF...THEN...ELSE... capability.  In XFormDBF, this can be used to construct simple initialization and cleanup expressions.
possave/posrest.prg
generic UDFs for saving and restoring a record position in a VFP workspace.  These are used in numerous places throughout SpaceTime's VFPUtils.  (Such a feature really should have been built into VFP.)
usetable.prg
generic UDF wrapper for VFP's USE command.  This provides a more convenient function interface, returning a success flag result to indicate whether opening was successful.  In XFormDBF, this can be used to construct simple initialization and cleanup expressions.

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