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How to Set A Default Value In Graphql?

7 minutes read

In GraphQL, you can set a default value for a field by using the defaultValue property when defining the field in your schema. The defaultValue property allows you to provide a default value that will be returned if the field is not explicitly set when querying the GraphQL API. This can be useful for ensuring that certain fields always have a value, even if one is not provided in the query.


For example, you can set a default value for a field like this:

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Field: {
  someField: {
    type: String,
    defaultValue: "Default Value"
  }
}


In this example, if the someField is not provided in the query, the default value of "Default Value" will be returned. This allows you to ensure that the field always has a value, even if it is not explicitly set in the query.


How to set default values for input nullable fields in GraphQL mutations?

In GraphQL, you can set default values for input nullable fields in mutations by using the "defaultValue" directive in your schema definition. Here's an example of how to set default values for input fields in a GraphQL mutation:

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input CreateUserInput {
  username: String!
  email: String
  password: String
    @defaultValue(value: "password123") // Set default value for password field
}

type Mutation {
  createUser(input: CreateUserInput!): User
}


In this example, the "defaultValue" directive is used to set a default value of "password123" for the "password" field in the "CreateUserInput" input type. This means that if the "password" field is not provided in the input object when calling the "createUser" mutation, it will default to "password123".


You can define default values for any nullable input fields in your mutations by adding the "defaultValue" directive to the field definition in your schema. This allows you to provide a default value for any input field that is not explicitly specified in the input object.


How to set global default values for all fields in a GraphQL schema?

In a GraphQL schema, you can set global default values for all fields by using the DefaultValuesPlugin from the @envelop/default-values package. Here's how you can set it up:

  1. Install the @envelop/default-values package by running the following command:
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npm install @envelop/default-values


  1. Import the necessary modules in your code:
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import { envelop } from '@envelop/core';
import { useDefaultValues } from '@envelop/default-values';


  1. Create a new instance of the DefaultValuesPlugin and pass in the default values that you want to set for all fields:
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const defaultValuesPlugin = useDefaultValues({
  defaultValues: {
    // Set default values for specific types or fields
    // For example, setting default value for String fields to "Default Value"
    String: 'Default Value',
    // You can also use functions to set dynamic default values
  },
});


  1. Create a new Envelop instance and pass in the DefaultValuesPlugin to set the default values globally:
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const getEnveloped = envelop({
  plugins: [
    defaultValuesPlugin,
    // Add other plugins as needed
  ],
});


  1. Now you can use the getEnveloped instance to execute your GraphQL queries and the default values will be set for all fields in your schema:
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// Execute GraphQL queries here


By following these steps, you can easily set global default values for all fields in your GraphQL schema using the @envelop/default-values package.


How to set default values for input custom scalars in GraphQL mutations?

In GraphQL, the default values for input custom scalars can be set in the mutation definition itself. You can achieve this by specifying the default value directly in the input type definition in the schema.


For example, let's say you have a custom scalar called CustomDate that represents a date value, and you want to set a default value for it in your mutation. Here's how you can do it in your schema definition:

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input CreatePostInput {
  title: String!
  content: String
  createdAt: CustomDate = "2022-01-01"
}

type Mutation {
  createPost(input: CreatePostInput!): Post
}


In this example, we have defined a CreatePostInput input type that includes a createdAt field of type CustomDate. We have set a default value of "2022-01-01" for this field in the schema.


When a mutation is executed without providing a value for createdAt, the default value "2022-01-01" will be used automatically.


Keep in mind that not all GraphQL server implementations support custom scalar default values out of the box. You may need to handle default values in your resolver functions if your GraphQL server does not support it.


How to handle default values in GraphQL subscriptions?

In GraphQL subscriptions, default values can be handled in a few different ways:

  1. Use a default value in the schema definition: You can define default values for subscription fields in the schema definition. This allows clients to omit the field in their subscription query and still receive the default value when the subscription data is received.
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type Subscription {
  newMessage(roomId: ID!): Message
}


  1. Set default values in the resolver function: When implementing the resolver function for a subscription field, you can check if the value is provided by the client and return a default value if it is not. This way, you can ensure that the subscription always returns a value, even if the client does not provide an argument.
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const resolvers = {
  Subscription: {
    newMessage: {
      subscribe: (parent, args, context) => {
        const { roomId } = args;
        const defaultValue = { id: 'default', content: 'Default message' };

        if (!roomId) {
          return defaultValue;
        }

        // Subscription logic here
      },
    },
  },
};


  1. Use a combination of both approaches: Depending on your use case, you can combine setting default values in the schema definition and in the resolver function to handle default values in subscriptions.


By implementing one or a combination of these approaches, you can ensure that your GraphQL subscriptions always return default values if no explicit value is provided by the client.


How to set dynamic default values in GraphQL?

In GraphQL, default values can be set using the defaultValue property in the schema definition. This value can be a static value or a dynamic value derived from a function.


To set dynamic default values, you can create a function that calculates the default value based on the current context or input data. For example, you can create a function that reads the current user's data from the request context and returns a default value based on that information.


Here's an example of setting dynamic default values in GraphQL:

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import { GraphQLObjectType, GraphQLSchema, GraphQLString } from 'graphql';

// Function to calculate dynamic default value
function calculateDefaultValue(root, args, context) {
  return context.currentUser.role === 'admin' ? 'admin' : 'user';
}

const userType = new GraphQLObjectType({
  name: 'User',
  fields: {
    role: {
      type: GraphQLString,
      defaultValue: calculateDefaultValue,
    },
  },
});

const queryType = new GraphQLObjectType({
  name: 'Query',
  fields: {
    currentUser: {
      type: userType,
      resolve(parent, args, context) {
        return context.currentUser;
      },
    },
  },
});

const schema = new GraphQLSchema({
  query: queryType,
});


In this example, the calculateDefaultValue function is used to calculate the default value for the role field based on the current user's role. The defaultValue property in the schema definition for the role field references this function. When a new User object is created without a role value, the default value will be dynamically calculated based on the current user's role.


By setting dynamic default values in this way, you can ensure that the default values provided by your GraphQL API are always up-to-date and relevant to the current context.


How to set a default value in GraphQL for a custom scalar field?

In GraphQL, you can set a default value for a custom scalar field by using the default keyword in the schema definition. Here's an example of how you can set a default value for a custom scalar field called CustomScalar in your schema:

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scalar CustomScalar

type MyType {
  customField: CustomScalar = "default value"
}


In this example, the field customField in the MyType type has a default value of "default value" for the custom scalar type CustomScalar. When a query is made and the customField field is not provided, the default value "default value" will be returned for that field.


Keep in mind that not all GraphQL implementations support setting default values for custom scalar fields in this way. You may need to handle default values in your application code if your GraphQL implementation does not support this feature.

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