selected index not valid in dropdown

i everyone ,

i am pratik and i am trying to build one form where user can search the candidate from dropdown which is comes throw database using query rule. and on selection of that choice  i want to display the all information of that perticular person in read only component .  and after that i want to add some more component in interface and store that into other table . but when i refresh my page that time i get the below errors.

Could not display interface. Please check definition and inputs. Interface Definition: Expression evaluation error at function a!integerField [line 42]: Invalid index (-2147483647) for list: valid range is 1..3

load(
  local!availableCandidates:rule!dms_query_demo(),
  local!selectedCandidate,
  local!selectedIndex,
  local!selectedTitle,
  a!formLayout(
  label: "Document Uploading page",
  contents: {
    a!columnsLayout(
      columns: {
        a!columnLayout(
          contents: {
            a!dropdownField(
              label: "Class",
              labelPosition: "ABOVE",
              placeholder: "--- Select the Class ---",
              choiceLabels: local!availableCandidates.name,
              choiceValues:  local!availableCandidates.name,
              value: local!selectedCandidate,
             
              saveInto: {
                local!selectedCandidate,
                a!save(local!selectedTitle, null),
                a!save(local!selectedIndex, wherecontains(local!selectedCandidate, local!availableCandidates.name))
              }
            )
            
          }
        ),
        a!columnLayout(
          contents: {}
        )
      }
    ),
    a!boxLayout(
      label: " Student information",
      contents: {
        a!columnsLayout(
          columns: {
            a!columnLayout(
              contents: {
                a!integerField(
                  label: "Student Id",
                  labelPosition: "ABOVE",
               
                  value: local!availableCandidates.id[local!selectedCandidate],
                  saveInto:ri!dms_student.id ,
                  refreshAfter: "UNFOCUS",
                  readOnly: true,
                  disabled: true,
                  validations: {}
                ),
                a!textField(
                  label: "Address",
                  labelPosition: "ABOVE",
                  value: local!availableCandidates.address[local!selectedIndex],
                  saveInto: ri!dms_student.address,
                  readOnly: true,
                  disabled: true,
                  validations:{}
                ),
                a!textField(
                  label: "Mob",
                  labelPosition: "ABOVE",
                  value: local!availableCandidates.mob[local!selectedIndex],
                  saveInto: ri!dms_student.mob,
                  disabled: true,
                  readOnly: true,
                  validations: {}
                )
              }
            ),
            a!columnLayout(
              contents: {
                a!textField(
                  label: "Name",
                  labelPosition: "ABOVE",
                  value: local!availableCandidates.name[local!selectedIndex],
/**/
                  saveInto: ri!dms_student.name,
                  disabled: true,
                  readOnly: true,
                  validations:{}
                ),
                a!textField(
                  label: "Department",
                  labelPosition: "ABOVE",
                  value: local!availableCandidates.department[local!selectedIndex],
                  saveInto: ri!dms_student.department,
                  disabled: true,
                  readOnly: true,
                  validations: {}
                ),
                a!textField(
                  label: "Class",
                  labelPosition:  "ABOVE",
                   
                   
                  
                  value: local!availableCandidates.class[local!selectedIndex],
                  saveInto: ri!dms_student.class,
                  readOnly: true,
                  
                  disabled: true,
                  validations: {}
                )
              }
            )
          }
        )
      },
      style: "#9900ff",
      marginBelow: "STANDARD"
    ),
    a!columnsLayout(
      columns: {
        a!columnLayout(
          contents: {
            a!dropdownField(
              label: "Document Type",
              labelPosition: "ABOVE",
              placeholder: "--- Select a Document ---",
              choiceLabels: cons!dms_doc_type_cons,
              choiceValues: cons!dms_doc_type_cons,
              value: ri!dms_document.type,
            
              saveInto: ri!dms_document.type,
              searchDisplay: "AUTO",
              validations: {}
            )
          }
        ),
        a!columnLayout(
          contents: {
            a!fileUploadField(
              label: "Upload Document Here..",
              labelPosition: "ABOVE",
              target: cons!dms_document_folder_cons,
              value: ri!dms_document.document,
            
              saveInto:ri!dms_document.document,
              validations: {}
            )
          }
        )
      }
    )
  },
  buttons: a!buttonLayout(
    primaryButtons: {
      a!buttonWidget(
        label: "Submit",
        /*saveInto: a!save(ri!dms_student, local!availableCandidates[local!selectedIndex]),*/
        submit: true,
        style: "PRIMARY"
      )
    },
    secondaryButtons: {
      a!buttonWidget(
        label: "Cancel",
        value: true,
        submit: true,
        style: "NORMAL",
        validate: false
      )
    }
  
  )
)
)