Dear professor,

In the Assignment model class, I have "url" data field since each assignment should be displayed as a hyperlink in the website. When I try to run the project on the server, it gives me this error:

org.postgresql.util.PSQLException: ERROR: column assignment4_.url does not exist
  Position: 839
	org.postgresql.core.v3.QueryExecutorImpl.receiveErrorResponse(QueryExecutorImpl.java:2102)
	org.postgresql.core.v3.QueryExecutorImpl.processResults(QueryExecutorImpl.java:1835)
	org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:257)
	org.postgresql.jdbc2.AbstractJdbc2Statement.execute(AbstractJdbc2Statement.java:500)
	org.postgresql.jdbc2.AbstractJdbc2Statement.executeWithFlags(AbstractJdbc2Statement.java:388)
	org.postgresql.jdbc2.AbstractJdbc2Statement.executeQuery(AbstractJdbc2Statement.java:273)
	org.hibernate.jdbc.AbstractBatcher.getResultSet(AbstractBatcher.java:208)
	org.hibernate.loader.Loader.getResultSet(Loader.java:1953)
	org.hibernate.loader.Loader.doQuery(Loader.java:802)
	org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:274)
	org.hibernate.loader.Loader.doList(Loader.java:2533)
	org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2276)
	org.hibernate.loader.Loader.list(Loader.java:2271)
	org.hibernate.loader.hql.QueryLoader.list(QueryLoader.java:452)
	org.hibernate.hql.ast.QueryTranslatorImpl.list(QueryTranslatorImpl.java:363)
	org.hibernate.engine.query.HQLQueryPlan.performList(HQLQueryPlan.java:196)
	org.hibernate.impl.SessionImpl.list(SessionImpl.java:1268)
	org.hibernate.impl.QueryImpl.list(QueryImpl.java:102)
	org.hibernate.ejb.QueryImpl.getResultList(QueryImpl.java:246)
	org.hibernate.ejb.criteria.CriteriaQueryCompiler$3.getResultList(CriteriaQueryCompiler.java:260)
	csns.model.academics.dao.jpa.SectionDaoImpl.getSections(SectionDaoImpl.java:166)
	csns.model.academics.dao.jpa.SectionDaoImpl.getSectionsByInstructor(SectionDaoImpl.java:66)
	sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
	sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
	java.lang.reflect.Method.invoke(Unknown Source)
	org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:309)
	org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:183)
	org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:150)
	org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:155)
	org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
	org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:202)
	$Proxy50.getSectionsByInstructor(Unknown Source)
	csns.web.controller.instructor.SectionController.viewSections(SectionController.java:78)
	sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
	sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
	java.lang.reflect.Method.invoke(Unknown Source)
	org.springframework.web.bind.annotation.support.HandlerMethodInvoker.invokeHandlerMethod(HandlerMethodInvoker.java:176)
	org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod(AnnotationMethodHandlerAdapter.java:426)
	org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.handle(AnnotationMethodHandlerAdapter.java:414)
	org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:790)
	org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:719)
	org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:644)
	org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:549)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
	org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:368)
	org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:109)
	org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:83)
	org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:380)
	org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:97)
	org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:380)
	csns.security.filter.RequestLoggingFilter.doFilterInternal(RequestLoggingFilter.java:37)
	org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)
	org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:380)
	org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:100)
	org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:380)
	org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:78)
	org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:380)
	org.springframework.security.web.authentication.rememberme.RememberMeAuthenticationFilter.doFilter(RememberMeAuthenticationFilter.java:119)
	org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:380)
	org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:54)
	org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:380)
	org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:35)
	org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:380)
	org.springframework.security.web.authentication.www.BasicAuthenticationFilter.doFilter(BasicAuthenticationFilter.java:177)
	org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:380)
	org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:187)
	org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:380)
	org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:105)
	org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:380)
	org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:79)
	org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:380)
	org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:169)
	org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:237)
	org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:167)
	org.springframework.orm.jpa.support.OpenEntityManagerInViewFilter.doFilterInternal(OpenEntityManagerInViewFilter.java:113)
	org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)

When I take out the url field from the Assignment class, the code works perfectly alright!!!

Any suggestions?