hospital_demo_py/models/hos_visit.xml

<model name="hos.visit" string="Visit">
  <field name="date" string="Date" type="date" required="1" search="1"/>
  <field name="other_patients" string="Other Patients" type="many2many" relation="hos.patient"/>
  <field name="patient_id" string="Patient" type="many2one" relation="hos.patient" search="1"/>
  <field name="state" string="Status" type="selection" selection="[[&quot;planned&quot;,&quot;Planned&quot;],[&quot;done&quot;,&quot;Completed&quot;]]" search="1" default="planned"/>
  <field name="xxx" string="XXX" type="char"/>
</model>