How to Set A Default Value In Graphql?

In GraphQL, you can set a default value for a field by providing a defaultValue property when defining the field in your schema. This defaultValue will be used as the value for the field if no value is provided in the query.

For example, you can define a field with a default value like this:

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type Query {
  exampleField: String 
    defaultValue: "Hello, World!"
}

In this example, the field "exampleField" will have the default value of "Hello, World!" if no value is provided in the query.

Setting default values can be useful for ensuring a consistent response structure even when certain fields are not explicitly requested or provided in the query.

How to set a default value using Relay in graphql?

In Relay, you can set a default value for a field by defining a default value function in the environment object. This function can be used to provide a default value for a field in case the data is not available from the server.

Here's an example of how to set a default value using Relay in GraphQL:

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import { Environment, Network, RecordSource, Store } from 'relay-runtime';

function fetchQuery(operation, variables) {
  // Your fetch implementation here
}

const network = Network.create(fetchQuery);
const source = RecordSource.create();
const store = new Store(source);

const environment = new Environment({
  network,
  store,
  missingFieldHandlers: [{
    handle: field => {
      // Define a default value for the field here
      return 'Default Value';
    },
  }],
});

export default environment;

In the code above, we created an environment object with a missingFieldHandlers property that contains a default value function. This function will be called for any field that is missing in the response from the server, and it can return a default value for that field.

You can customize the default value function to provide different default values for specific fields or conditions as needed.

What are some common use cases for setting default values in graphql?

1. Providing a default value for an optional argument in a query or mutation, so that the field can still be queried even if the argument is not provided.
2. Setting default values for fields in a query response, so that clients can still receive data even if the requested fields are not available.
3. Using default values for pagination arguments, such as setting a default limit or offset for paginated queries.
4. Setting default values for input fields in mutations, so that certain fields can be pre-populated for the user.
5. Using default values for filter arguments in queries, so that clients can retrieve a subset of data without explicitly specifying all filter criteria.

How to set a default value using Apollo client in graphql?

To set a default value for a field in Apollo Client, you can use the default option in the field's configuration when defining your GraphQL schema. Here is an example of how you can set a default value for a field using Apollo Client:

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const typeDefs = gql`
  type Query {
    hello(name: String): String
  }
`;

const resolvers = {
  Query: {
    hello: (_root, { name }, _context, _info) => {
      return `Hello, ${name || 'World'}!`;
    },
  },
};

const client = new ApolloClient({
  cache: new InMemoryCache(),
  link: new HttpLink({
    uri: 'http://localhost:4000/graphql',
  }),
  typeDefs,
  resolvers,
});

client.writeData({
  data: {
    hello: 'Default Value',
  },
});

In this example, we have defined a hello field in the Query type with a default value of 'World'. When the hello resolver function is called and the name argument is not provided, it will use the default value 'World'. Additionally, we use client.writeData to set a default value for the hello field in the Apollo Client cache.