Q:

How set computed property of checked checkboxes via v-model?

I've looked several resources, but I don't find the solution:

https://vuejs.org/v2/guide/computed.html
V-model with props & computed properties
vuejs v-model, multiple checkbox and computed property

I've a table with people that have roles, if I want to change the roles I open a modal. 
<template>
  <div>
    <b-table small outlined striped hover :items="peoplePaginated.data" :fields="fields" >
      <template slot="actions" slot-scope="row">
        <b-button size="sm" class="my-2 my-sm-0 btn-outline-info" v-b-modal="'federation-role-modal'" @click.stop="change(row.item)">
        edit
        </b-button>
        <b-button size="sm" @click.stop="info(row.item, row.index, $event.target)" class="btn btn-outline-success btn-sm">
          details
        </b-button>
      </template>
    </b-table>
    <FederationRoleModal :roles="roles" />
  </div>
</template>

data () {
 return {
    roles: [],
 }
},

  methods: {
    info (item) {
      this.$router.push({ name: 'person', params: { id: item.id }})
    },
    change (person) {
      const roles = person.personRoles.map(el => el)
      const allRoles = roles.map(el => el.roleCategory.name)
      this.roles = allRoles
    }
  }

Then I've a list of checkboxes where the checkedRoles takes care of the checked ones. When I click on a new checkbox, I want the data property to be updated. However this updating does not happen.
In the modal:
<span v-for="value in allRoles" :key="value.id">
    <input type="checkbox" :value="value" v-model="checkedRoles">
    <span class="checkbox-label"> {{value}} </span> <br>
</span>

computed property: {
  checkedRoles: {
    get: function () {
      // console.log(this.roles)
      return this.roles
    },
    set: function (newValue) {
      // console.log(newValue)
      return newValue
    }
  }
}

this.roles comes from the parent component (array with roles). 
I do see the console.log(newValue) output as a new array with an additional role, but this new array is not visible as the checkedRoles data property.

[option 2] I've also tried to add checkedRoles: this.roles, in the data () { return {... }. But when I open several times a modal, the roles of the previous clicked row.item are still in the data property.

Please advise 

if I should be using a computed property, or dig deeper into [option 2]
how I get all checked checkboxes to be in the checkedRoles data property.

A:

Solution included modifying the parent component data property:
In the parent component add:
<FederationRoleModal :checked-roles="roles" @update-role="onUpdateRole"/>

methods:
    onUpdateRole(value) {
      let rolesArray = this.roles
      if (rolesArray.includes(value)){
        var index = rolesArray.indexOf(value)
        if (index > -1) {
          return rolesArray.splice(index, 1);
        }
      } else {
        return rolesArray.push(value)
      }
    }

in the child component
      <span v-for="value in allRoles" :key="value.id">
        <input type="checkbox" :value="value" v-model="roles" @click="$emit('update-role', value)">
        <span class="checkbox-label"> {{value}} </span> <br>
      </span>

data:
props: ['checkedRoles'],

computed:
roles: {
  get: function () {
   return this.checkedRoles
 },
 set: function (newValue) {
   return newValue
 }
}

