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Property :: previous - Try selecting previous instance in collection

The function locates and reads the previous instance in a collection starting from the currently located one. When no instance is located, the function selects the last valid instance.

When a filter has been defined for the collection, the function returns the previous valid instance according to the filter condition.

The function returns true , when previous instance has been located successfully. Otherwise it returns false . In case of read errors or when the property handle is not accessible the function throws an exception.

Notes:

Since error handling in previous() loops becomes difficult, a better way of iterating through a collection is often using get( iPosition ) or getRelative( iPosition ) and count() or relativeCount() in order to determin the size of collection.

Return value:  Success ( bool  )

The value is true when the function was executed successfully. Otherwise the value is set to false .

Implementation overview

Implementation details

  1. Locate previous instance
    bool Property  :: previous (  )

    The function locates the previous instance in the property handle without reading it. The instance might be selected when a filter has been set for the property handle.

    In order to make sure that the instance is selected, one may call get() or previous(true).

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  2. Locate previous instance for key level
    bool Property  :: previous ( int32 iKeyLevel, bool bRead )

    The switch level ( iKeyLevel ) allows defining the last key components that must alter. This allows e.g. providing all instances without duplicate key values, when fixing the last key component.

    • iKeyLevel - Number of fixed key component

      The switch level defines the key component number that need not change when calling next() or locateKey() beginning with 1 for the first key component.

    • bRead - Read option

      The option forces the function to read the instance when it could be located.

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  3. Locate and read previous instance
    bool Property  :: previous ( bool bRead )

    The function locates and reads the previous instance, when passing true in bRead . When passing false , the function tries to locate the instance without reading.

    • bRead - Read option

      The option forces the function to read the instance when it could be located.

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