Does a city have to enforce its own building bylaw against a person with knowledge that he is in contraven tion of the bylaw?

The defendant referred the court to the case of City of Kamloops v. Nielsen et al., [1984] 2 S.C.R. 2; 54 N.R. 1; 10 D.L.R.(4th) 641; [1984] 5 W.W.R. 1. That case deals with a building bylaw which provided for a scheme of inspections by the city's inspectors. The evidence proved that the city was aware of the defective construction and the court held that in those circumstances, the city was obliged to take care not to injure persons such as the plaintiffs who had purchased the property from a previous owner. In the case before me the defendant knew that the land was not zoned for his business use but was allowed to continue the use for appar ently nine years. I am not aware of any law which requires the plaintiff to enforce its bylaws against a person with knowledge that he is in contraven tion of the bylaw.