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    Reuse GraphQL Selection Sets with Fragments


    Fragments are selection sets that can be used across multiple queries. They allow you to refactor redundant selection sets, and they are essential when querying unions or interface types. In this lesson, we will improve our query logic by creating a fragment for the activity selection set.

    To follow along with these queries, go to the Pet Library GraphQL Playground.



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    Instructor: Let's start by adding a query for all pets, and we want to filter this by category. We'll look for all the rabbits, and we'll also filter by status to find the available rabbits. Next, we want to select a few fields.

    We'll grab name, weight, and category, and we should see all of these available rabbits. We also want to grab their status. If only there was a way in the GraphQL query language to make all of these selection sets a little bit more reusable.

    The good news is, there is. I'm going to create a fragment called petDetails. Think of a fragment of being a wrapper around several fields. petDetails is going to be a fragment on a certain type. This is going to be for pet.

    Then we're going to cut and paste all of these fields into the fragment, and we'll use spread syntax, ..., to push all of the pet details into this query. We're able to send the query and see that all of the field are still being sent with the query.

    Now, we can also adjust the fragment to add additional fields. If I wanted to grab the photo as well as the thumbnail, we can see that the thumbnail for the photo is being returned. Let's add onto this query a little bit and add petByID.

    We're going to look for the pet C1, and here, we can reuse petDetails inside of the query so that we don't have to retype them. There we go, we get all of those fields for that pet. You can also add additional fields alongside your fragment.

    Let's add inCareOf, name, and username. We should see the person who has checked out this pet. Since we're having so much fun with fragments, we can create a fragment for customer details. We're going to specify that these fields come from the customer type, and we can add name and username from inCareOf.

    We can then push those fields into the query, hit prettify to get rid of that spacing issue again, and click play. We see all of those fields are being returned. We created a fragment called petDetails. This will take all of these fields and put them into the query.

    Then we have another forCustomerDetails. All of the fields we want are going to be pushed into the query when we use that fragment syntax, ..., and then the name of the fragment.