Detect new todos

In this section we will capture newly added public todos in the database. This can be done by subscribing to the last todo added in the database. The subscription query looks like:

Copy
subscription {
  todos (
    order_by: {
      id: desc
    }
    limit: 1
    where: { is_public: { _eq: true }}
  ) {
    id
  }
}

What does this subscription do?

The above subscription gives only the "last added" element in the database (ordered by id and limit set to 1). So whenever a todo is added in the database, this subscription will receive data.

We can treat this subscription data as an event notification saying "something has been added" and fetch all the todos from the database newer than the newest todo present in the local cache.

Whenever such an event notification occurs, we can fetch the newer todos with the following query:

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query ($lastId: Int){
  todos (
    order_by: {
      id: desc
    },
    where: {
      _and: {
        is_public: { _eq: true},
        id: { _gt: $lastId}
      }
    }
  ) {
    id
    title
    is_completed
    created_at
    is_public
    user {
      name
    }
  }
}

What does this query do?

This query takas a query variable called $lastId and fetches all the todos with id greater than the value of $lastId.

Now let us wire up this functionality in our app.