A miniature microphone directly on a violin 
For live use (or home studio) the
d:vote™ 4099V clip mic may well be the ideal solution. The 4099V has a supercardioid polar pattern that allows the mic to focus on the instrument and get a good isolation from the other sound sources on the stage or bad acoustics. This also reduces the risk of feedback significantly, while keeping the rich and nuanced sound of the instrument uncolored.
However, because of its high directionality some time should be spent on finding the right placement for the
mic. The position will always be a compromise trying to capture the whole instrument with a narrow pick up pattern.
The VC4099 violin clip included with the 4099V offers a unique solution that is both secure, highly flexible (fits also viola, mandolin & banjo) and very gentle to the instrument.
An even smaller and yet superbly sounding microphone is the
miniature 4061 omnidirectional microphone.