We have a case for our Sony Nex 5R wanted, where we can not only the camera but also all accessories and an extra lens to accommodate safely. Three other bags were returned as not ideal. This remains. Clean design and well thought-out this bag, with a good comfort. A real recommendation!
This bag is the same as offered here at Amazon for both the Nikon D3100 as well as Premium bag for system cameras, the only difference is in the price. So it's worth, again to look closely before buying.