Mutations

While GraphQL queries perform read operations, mutations change the data. A mutation can create, update, or delete objects and fields. In REST terminology, queries operate like GET requests, while mutations are similar to POST, PUT, and DELETE.

Structure of a mutation

A mutation contains the following elements:

  • The keyword mutation
  • An operation name for your local implementation. This name is required if you include variables. Otherwise, it is optional.
  • The mutation name
  • The input object or attributes. Most mutations require an input object that contains data or individual attributes for the Magento server to process. However, some mutations, such as createEmptyCart, do not require an input object. In this particular case, the authorization token passed with the request provides the needed context.
  • The output object, which specifies which data the mutation returns.

The following example shows the structure of the createCustomer mutation:

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mutation myCreateCustomer{
    createCustomer(
        input: CustomerInput!): CustomerOutput
    }
}

In this example, myCreateCustomer identifies your implementation. CustomerInput is a non-nullable object that defines a customer. (The exclamation point indicates the value is non-nullable.) The CustomerOutput object defines which fields to return.

Now let’s take a look at a fully-defined mutation. This time, we’ll specify the minimum fields needed as input to create a customer (firstname, lastname, email, and password). We could include the same fields in the output, but GraphQL allows you to return only the data you need, which is the customer id.

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mutation myCreateCustomerNoVariables{
    createCustomer(
        input: {
            firstname: "Melanie"
            lastname: "Shaw"
            email: "mshaw@example.com"
            password: "Password1"
        }
    ) 
    {
        customer {
            id
        }
    }
}

The mutation returns the customer ID:

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{
  "data": {
      "createCustomer": {
          "customer": {
              "id": 2
            }
        }
    }
}

Mutation input

A mutation can require either an object as input (as shown above) or one or more scalar values. When specifying an object, you must include the input: {} keyword. When the mutation requires scalar values, specify the field name and value, as shown below:

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mutation myGenerateCustomerToken{
    generateCustomerToken(
        email: "mshaw@example.com"
        password: "Password1"
    )
    {
        token
    }
}

Mutation variables

Specifying variables in a mutation can help increase code re-use. Consider the following requirements when generating a mutation that contains one or more variables:

  • All variables must be declared up-front, immediately after the operation name.
  • Variables are typed: they can be scalar or an object.
  • You must use all declared variables. Object variables are defined in JSON.

The following example declares the $CustomerInput variable. It is referenced in the input statement.

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mutation myCreateCustomerWithVariables($CustomerInput: CustomerInput!){
    createCustomer(
        input: $CustomerInput
    )
    {
        customer {
            id
        }
    }
}

The $CustomerInput variable is defined as a JSON object:

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{
"CustomerInput": {
    "firstname": "Melanie",
    "lastname": "Shaw",
    "email": "mshaw@example.com",
    "password": "Password1"
   }
}

This example updates the customer’s email using two scalar variables ($email, $password).

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mutation myUpdateCustomer($email: String!, $password: String!){
    updateCustomer(
        input: {
            email: $email
            password: $password
        }
    )
    {
        customer {
            id
            email
        }
    }
}

The variables are defined separately.

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{
    "email": "melanie.shaw@example.com",
    "password": "Password1"
}