我在使用EF更新期间遇到以下错误:Theoperationfailed:Therelationshipcouldnotbechangedbecauseoneormoreoftheforeign-keypropertiesisnon-nullable.Whenachangeismadetoarelationship,therelatedforeign-keypropertyissettoanullvalue.Iftheforeign-keydoesnotsupportnullvalues,anewrelationshipmustbedefined,theforeign-keyproper

我在使用EF更新期间遇到以下错误:Theoperationfailed:Therelationshipcouldnotbechangedbecauseoneormoreoftheforeign-keypropertiesisnon-nullable.Whenachangeismadetoarelationship,therelatedforeign-keypropertyissettoanullvalue.Iftheforeign-keydoesnotsupportnullvalues,anewrelationshipmustbedefined,theforeign-keyproper