Vuetify rendering v-datatable automatically

Question

I have a problem v-datatable rendering each time I change a v-select.

I´d like it render only when I click in a button, I created to do fetch data from server.

Here is the codepen: https://codepen.io/luizalves/pen/VwrwXwE?editors=101

For now, it´s rendering all times I change the v-select.

data:()=>({
grupos: [
      { id: 1, nome: 'Diário', ffi: 'YYYY-MM-DD', fff: 'DD-MM-YYYY' },
      { id: 2, nome: 'Mensal', ffi: 'YYYY-MM', fff: 'MM-YYYY' },
      { id: 3, nome: 'Anual', ffi: 'YYYY', fff: 'YYYY' },
    ],
grupo:1
headers: [
      { text: 'Data', value: 'label', sortable: false },
      { text: 'Total(R$) ', value: 'total', sortable: false },
    ],
)}

// data-table

        <v-select
              v-model="grupo"
              label="Grupado por"
              :items="grupos"
              item-text="nome"
              item-value="id"
              class="purple-input"
            />
 <v-btn
        class="mt-1 mr-3"
        color="info"
        @click.stop="getEstatisticasPeriodo()"
      >
        Pesquisar
      </v-btn>
    <v-data-table
                  :headers="headers"
                  :items="result_dados"
                  :items-per-page="3"
                  :footer-props="{
                    'items-per-page-options': [3, 5, 10, 20, 30, 40, 50],
                  }"
                  class="elevation-1"
                >
                  <template
                    v-for="(header, i) in headers"
                    #[`item.${header.value}`]="{ item }"
                  >
                    <template v-if="header.value !== 'actions'">
                      <span :key="i">
                        {{ formatColumn(item, header) }}
                      </span>
                    </template>
                  </template>
         </v-data-table>
 methods: {
    formatColumn(item, col) {
      if (!item[col.value]) return ''
      if (['total'].includes(col.value)) {
        const formatado = Number(item[col.value]).toLocaleString('pt-BR', {
          style: 'currency',
          currency: 'BRL',
        })
        return formatado
      }
      if (['label'].includes(col.value)) {
        const ffi = this.grupos.find((m) => m.id == this.grupo).ffi
        const fff = this.grupos.find((m) => m.id == this.grupo).fff
        return this.$moment(item[col.value], ffi).format(fff)
      } else return item[col.value]
    },
getEstatisticasPeriodo(){
        // fetch api data
}
....

Answer 1

Any data value you access in formatCalories will be added the list of watched values. When the value changes, it will re-render the view and call formatCalories. To solve that issue, I just created a selectValue property that is only set when the button is clicked.

new Vue({
  el: '#app',
  vuetify: new Vuetify(),
  data () {
    return {
      group: 1,
      selectValue: 1,
      groups: [
       { id: 1, name: 'day'},
       { id: 2, name: 'month' },
       { id: 3, name: 'year' },
      ],
      headers: [
        {
          text: 'Dessert (100g serving)',
          align: 'start',
          sortable: false,
          value: 'name',
        },
        { text: 'Calories', value: 'calories' },
        { text: 'Fat (g)', value: 'fat' },
        { text: 'Carbs (g)', value: 'carbs' },
        { text: 'Protein (g)', value: 'protein' },
        { text: 'Iron (%)', value: 'iron' },
      ],
      desserts: [
        {
          name: 'Frozen Yogurt',
          calories: 159,
          fat: 6.0,
          carbs: 24,
          protein: 4.0,
          iron: '1%',
        },
        {
          name: 'Ice cream sandwich',
          calories: 237,
          fat: 9.0,
          carbs: 37,
          protein: 4.3,
          iron: '1%',
        },
        {
          name: 'Eclair',
          calories: 262,
          fat: 16.0,
          carbs: 23,
          protein: 6.0,
          iron: '7%',
        },
        {
          name: 'Cupcake',
          calories: 305,
          fat: 3.7,
          carbs: 67,
          protein: 4.3,
          iron: '8%',
        },
        {
          name: 'Gingerbread',
          calories: 356,
          fat: 16.0,
          carbs: 49,
          protein: 3.9,
          iron: '16%',
        },
        {
          name: 'Jelly bean',
          calories: 375,
          fat: 0.0,
          carbs: 94,
          protein: 0.0,
          iron: '0%',
        },
        {
          name: 'Lollipop',
          calories: 392,
          fat: 0.2,
          carbs: 98,
          protein: 0,
          iron: '2%',
        },
        {
          name: 'Honeycomb',
          calories: 408,
          fat: 3.2,
          carbs: 87,
          protein: 6.5,
          iron: '45%',
        },
        {
          name: 'Donut',
          calories: 452,
          fat: 25.0,
          carbs: 51,
          protein: 4.9,
          iron: '22%',
        },
        {
          name: 'KitKat',
          calories: 518,
          fat: 26.0,
          carbs: 65,
          protein: 7,
          iron: '6%',
        },
      ],
    }
  },
  methods: {
    onSubmit() {
      this.selectValue = this.$refs.select.value;
    },
    formatCalories(calories) {
      const suffix = {
        1: '-red',
        2: '-orange',
        3: '-green'
      };
      
      return calories + suffix[this.selectValue];
    }
  },
})

<div id="app">
  <v-app id="inspire">
    <v-row>
      <v-col cols='3'>
    <v-btn elevation="2" @click="onSubmit"> Submit </v-btn>
    <v-select
          v-model="group"
          label="Grouped by"
          :items="groups"
          item-text="name"
          item-value="id"
          class="purple-input"
          ref="select"
        />
        </v-col>
      </v-row>
    <v-data-table
      :headers="headers"
      :items="desserts"
      class="elevation-1"
    >
      <template v-slot:item.calories="{ item }">
          {{ formatCalories(item.calories) }}
         </template>
    </v-data-table>
    
  </v-app>
</div>