Writing data - Mutations

These are the concepts you should know before you attack mutations (haha):

• Using GraphiQL
• Using query variables

Now, let's get started with seeing how we can use GraphQL to "write" data. GraphQL mutations are types of GraphQL queries that may result in the state of your backend "mutating" or changing, just like typical 'POST', 'PUT', 'PATCH', 'DELETE' APIs.

Basic mutations

Since we're using Hasura for our GraphQL API, we get mutations for insert, updates or deletes that we can use in our app.

Let's try these mutations out in the context of a todo app to see what mutations look like. Mutations that you get from another GraphQL service, say if your API team has built their own, might be different.

Create a todo

Let's make an API call to create a todo. As you would have guessed, this will be a critical portion of our todo app. 😉

Protip: Now let's say we don't know what the name of the mutation to create a todo. GraphiQL to the rescue! Head to GraphiQL and on the right, click on the "docs" tab. Type "todo" there and you'll see a list of GraphQL queries and types that use todo. Read through their descriptions and you'll soon find that insert_todo is what you need.

The mutation to create todos is titled insert_todos.

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mutation {
  insert_todos(objects: [{title: "new todo"}]) {
    returning {
      id
    }
  }
}

Returning data after the mutation

Notice that the data of the todo that is to be inserted is sent as an argument to the insert_todos mutation. But the "fields" of the mutation specify the shape of the response that you want from the server.

Let's say we'd like to get the entire todo object once it's been created as a response:

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mutation {
  insert_todos(objects: [{title: "new todo"}]) {
    returning {
      id
      title
      is_completed
      is_public
      created_at
    }
  }
}

Parameterise what you insert

For mutations, we would almost always have to paramatrise the arguments! We would rarely, if ever, have a "hardcoded" mutation in our app. This is because the arguments of what data to capture, how to modify or delete something is usually dependent on some user action.

Now that we know how to parameterise using query variables, let's use that:

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# The parametrised GraphQL mutation
mutation($todo: todos_insert_input!){
  insert_todos(objects: [$todo]) {
    returning {
      id
    }
  }
}

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# As a query variable
{
  "todo": {
    "title": "A new dynamic todo"
  }
}

We'll explore more mutations to update or delete data a little later. This is a good start to grokking mutations!

Summary

• You can make basic GraphQL mutations
• You can pass dynamic arguments/data to mutations with query variables

Next, let's look at GraphQL subscriptions