Put all ingredients except spaghetti and cheese into a slow cooker. Cover, and cook on low for seven to eight hours. Add a little more water if sauce gets too thick. One half hour before serving, bring a large pot of water to boil and add salt. Cook spaghetti according to package instructions. Drain thoroughly.

While spaghetti is cooking, remove any oil that has accumulated on top of the sauce with a spoon and discard. Remove sausages pieces from the slow cooker and cut them into thirds. Ladle the sauce over the cooked pasta in a large bowl. Arrange sausage pieces on top. Have grated Parmesan cheese on the table for sprinkling.