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How to Pass A Variable to Graphql Query?

5 minutes read

To pass a variable to a GraphQL query, you need to define the variable in the query itself. This is done by using a special syntax where you define the variable in the query and then provide its value when making the query request.


Here's an example of how you can pass a variable to a GraphQL query:

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query($variableName: Type) {
  queryName(input: $variableName) {
    field1
    field2
  }
}


In this example, $variableName is the variable that we want to pass to the query. When making the actual query request, you would provide the value for variableName like this:

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{
  "query": "queryName",
  "variables": {
    "variableName": "value"
  }
}


By passing the variable value in the variables object when making the query request, you can dynamically provide different values for the variable in your GraphQL queries.


How to pass a variable to a GraphQL query in Angular?

To pass a variable to a GraphQL query in Angular, you can use the variables property of the Apollo client service provided by Apollo Angular.


Here is an example of how you can pass a variable to a GraphQL query in Angular:

  1. First, import the Apollo client service in your component where you want to make the GraphQL query:
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import { Apollo } from 'apollo-angular';


  1. Inject the Apollo client service in your component's constructor:
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constructor(private apollo: Apollo) { }


  1. Define your GraphQL query with a variable placeholder. For example:
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query GetUser($userId: Int!) {
  user(id: $userId) {
    id
    name
  }
}


  1. Make the GraphQL query using the query method of the Apollo service and passing the variable in the variables property:
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this.apollo.query({
  query: gql`
    query GetUser($userId: Int!) {
      user(id: $userId) {
        id
        name
      }
    }
  `,
  variables: {
    userId: 1
  }
}).subscribe(result => {
  console.log(result.data);
});


In the example above, the variable userId with a value of 1 is passed to the GetUser query. The result of the GraphQL query is then logged to the console.


By following these steps, you can easily pass variables to GraphQL queries in Angular using the Apollo Angular client service.


What is the recommended way to handle variables in GraphQL queries?

It is recommended to pass variables as arguments to a GraphQL query in order to make queries more dynamic and parameterized. This allows for better separation of concerns and makes queries more reusable. Here is an example of how to pass variables to a GraphQL query:

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query GetUser($id: ID!) {
  user(id: $id) {
    name
    email
  }
}


In this example, the $id variable is defined in the query and its type is specified (in this case ID! meaning it is required). When executing the query, you would pass the value of the variable like so:

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{
  "id": "123"
}


By using variables in GraphQL queries, you can make your queries more dynamic and flexible, allowing you to easily reuse queries with different input values.


What is the behavior of GraphQL queries without variables?

GraphQL queries without variables typically consist of static, hard-coded values that are directly embedded into the query string. This means that the query will always request the same specific data every time it is executed. This can be useful for simple or one-off queries where the data being requested does not need to change dynamically.


However, using variables in GraphQL queries allows for more dynamic and flexible querying capabilities. Variables enable the query to be more reusable and adaptable by allowing the input values to be passed in separately from the query itself. This can make queries more efficient, maintainable, and easier to work with, especially in situations where the data being retrieved may vary based on different inputs or conditions.


How to define variables in a GraphQL query?

In a GraphQL query, you can define variables using the following syntax:

  1. Inside the query definition, specify the variable name preceded by the $ sign and its type in parentheses. For example:
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query ($id: ID!) {
  ...
}


  1. Declare the variable values in a separate JSON object in the query operation, where the key is the same as the variable name (without the $ sign). For example:
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{
  "id": 1
}


  1. Use the variable inside the query by replacing the hardcoded value with the variable name. For example:
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query ($id: ID!) {
  user(id: $id) {
    name
  }
}


  1. When sending the query to the GraphQL server, pass the variables object along with the query. The server will replace the variables in the query with the values provided.


How to pass a variable to a GraphQL query in Vue.js?

To pass a variable to a GraphQL query in Vue.js, you can use the apollo module provided by the Vue Apollo library. Here's a step-by-step guide on how to pass a variable to a GraphQL query in Vue.js:

  1. Install Vue Apollo:
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npm install vue-apollo graphql apollo-client apollo-link apollo-link-http apollo-cache-inmemory graphql-tag


  1. Set up Vue Apollo in your Vue.js app. You can do this in your main.js file:
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import Vue from 'vue'
import { ApolloClient } from 'apollo-client'
import { HttpLink } from 'apollo-link-http'
import { InMemoryCache } from 'apollo-cache-inmemory'
import { ApolloLink } from 'apollo-link'
import VueApollo from 'vue-apollo'

const httpLink = new HttpLink({
  uri: 'your graphql endpoint'
})

const apolloClient = new ApolloClient({
  link: ApolloLink.from([httpLink]),
  cache: new InMemoryCache()
})

Vue.use(VueApollo)

const apolloProvider = new VueApollo({
  defaultClient: apolloClient
})

new Vue({
  apolloProvider,
  render: h => h(App)
}).$mount('#app')


  1. Use the apollo option in your Vue component to define your GraphQL query with variables:
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<template>
  <div>
    <div v-if="loading">Loading...</div>
    <div v-else>
      <div v-for="user in users" :key="user.id">{{ user.name }}</div>
    </div>
  </div>
</template>

<script>
import gql from 'graphql-tag'

export default {
  apollo: {
    users: {
      query: gql`
        query getUsers($role: String!) {
          users(role: $role) {
            id
            name
          }
        }
      `,
      variables() {
        return {
          role: 'admin'
        }
      }
    }
  },
  data() {
    return {
      loading: false
    }
  }
}
</script>


In this example, we pass a variable called role to the getUsers query. The variables function returns an object with the variables to be passed to the query. You can also dynamically change the value of the variable based on user input or other data in your component.


That's it! You have successfully passed a variable to a GraphQL query in Vue.js using Vue Apollo.

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