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Mutation and update cache

Now let's do the integration part. Open src/components/Todo/TodoItem.res and add the following code to define the delete mutation

githubsrc/components/Todo/TodoItem.res
module RemoveTodoMutation = %graphql(`
mutation removeTodo($id: Int!) {
delete_todos(where: { id: { _eq: $id } }) {
affected_rows
}
}
`)

We have a function defined to handle the button click to remove a todo. Let's update the function to use removeTodoMutation mutate function.

let removeTodo = e => {
ReactEvent.Mouse.preventDefault(e)
ReactEvent.Mouse.stopPropagation(e)
removeTodoMutate(~update=({readQuery, writeQuery}, {data: _data}) => {
let existingTodos = readQuery(~query=module(TodosQuery), ())
switch existingTodos {
| Some(todosResult) =>
switch todosResult {
| Ok({todos}) => {
let newTodos = Js.Array2.filter(todos, t => t.id !== todo.id)
let _ = writeQuery(~query=module(TodosQuery), ~data={todos: newTodos}, ())
}
| _ => ()
}
| None => ()
}
}, {id: todo.id})->ignore
}

Let's pass optimistic response for instant UI update.

let removeTodo = e => {
ReactEvent.Mouse.preventDefault(e)
ReactEvent.Mouse.stopPropagation(e)
removeTodoMutate(
+ ~optimisticResponse=_variables => {
+ delete_todos: Some(
+ (
+ {
+ affected_rows: 1,
+ __typename: "todos_mutation_response",
+ }: RemoveTodoMutation.RemoveTodoMutation_inner.t_delete_todos
+ ),
+ ),
+ },
~update=({readQuery, writeQuery}, {data: _data}) => {
let existingTodos = readQuery(~query=module(TodosQuery), ())
switch existingTodos {
| Some(todosResult) =>
switch todosResult {
| Ok({todos}) => {
let newTodos = Js.Array2.filter(todos, t => t.id !== todo.id)
let _ = writeQuery(~query=module(TodosQuery), ~data={todos: newTodos}, ())
}
| _ => ()
}
| None => ()
}
},
{id: todo.id},
)->ignore
}
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