You might be conflating how an injector turns on and if with how the fuel is pressurized. Unit injectors create the high pressure for injection in the injector, combining the high pressure pump and injector in one, fed by a low pressure rail. Theses are driven mechanically via cams to create pressure.

Common high pressure rail injectors have a separate high pressure pump connected to engine elsewhere and the injectors just turn on and off fed by a high pressure common rail.

The injector itself can be actuated mechanically or via solenoids or piezo, but there are no injectors that create pressure electrically that I know of (the closest I have seen are voicemail medium pressure gas injectors used in ETEC engines). That is the electric part of the injector only lets the fuel through, it does not force it.