title: unable to start Grail application
body: <p>I am learning Grail and was trying to below code but could not start the application after referencing two classes make and model in vehicle class. also I am adding year as an integer in vehicle class </p>
  
  <pre><code>Running application...
  2017-03-05 08:48:32.229 ERROR --- [ost-startStop-1] o.s.b.c.embedded.tomcat.TomcatStarter    : Error starting Tomcat context. Exception: org.springframework.beans.factory.BeanCreationException. Message: Error creating bean with name 'grailsCacheFilter': Cannot create inner bean '(inner bean)#692e68e0' of type [grails.plugin.cache.web.filter.simple.MemoryPageFragmentCachingFilter] while setting bean property 'filter'; nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name '(inner bean)#692e68e0': Unsatisfied dependency expressed through method 'setUrlMappingsHandlerMapping' parameter 0; nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'urlMappingsHandlerMapping': Unsatisfied dependency expressed through method 'setWebRequestInterceptors' parameter 0; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'openSessionInViewInterceptor': Cannot resolve reference to bean 'hibernateDatastore' while setting bean property 'hibernateDatastore'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'hibernateDatastore': Bean instantiation via constructor failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.grails.orm.hibernate.HibernateDatastore]: Constructor threw exception; nested exception is org.hibernate.MappingException: 
  **Could not determine type for: groovy.lang.Binding, at table: vhicle, for columns: [org.hibernate.mapping.Column(binding)]**
  2017-03-05 08:48:32.392 ERROR --- [           main] o.s.boot.SpringApplication               : Application startup failed
  
  org.springframework.context.ApplicationContextException: Unable to start embedded container; nested exception is org.springframework.boot.context.embedded.EmbeddedServletContainerException: Unable to start embedded Tomcat
          at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.onRefresh(EmbeddedWebApplicationContext.java:137)
          at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:536)
          at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.refresh(EmbeddedWebApplicationContext.java:122)
  org.springframework.boot.SpringApplication.run(SpringApplication.java:315)
          at grails.boot.GrailsApp.run(GrailsApp.groovy:83)
          at grails.boot.GrailsApp.run(GrailsApp.groovy:387)
          at grails.boot.GrailsApp.run(GrailsApp.groovy:374)
          at grails.boot.GrailsApp$run.call(Unknown Source)
          at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:48)
  
  
  FAILURE: Build failed with an exception.
  
  * What went wrong:
  Execution failed for task ':bootRun'.
  Process 'command '/usr/lib/jvm/java-7-oracle/bin/java'' finished with non-zero exit value 1
  
  * Try:
  Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output.
  | Error Failed to start server (Use --stacktrace to see the full trace)
  </code></pre>
  
  <p>Here is my Vhicle.groovy</p>
  
  <pre><code>       package com.example
  
         class Vehicle {
  
          Integer year
  
          String name
          Model model
          Make make
  
          static constraints = {
              year min: 1900
              name maxSize: 255
          }
          }
  
         def vehicle = Vehicle.findByName('pickup')
          if(vehicle) {
          println vehicle.model // e.g, 'Titan'
          println vehicle.make // e.g, 'Nissan'
        }
  
        Model.groovy
  
        package com.example
  
        class Model {
  
          String name
  
          static belongsTo = [ make: Make ]
  
          static constraints = {
               }
  
          String to_String(){
              name
              }
          }
  
        Here is my Make.groovy
  
        package com.example
  
        class Make {
  
              String name
  
  
           static constraints = {
               }
  
              String to_String(){
                      name
              }
            }
  </code></pre>