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Fields can overlap when you are querying the same field with different arguments. In this video we will discuss the syntax for aliasing a field and show a query with the same field aliased twice.
Course repo: Use this GitHub repo to follow along with this video in the course
(Apollo's Launchpad has been deprecated, so your screen will look different)
New Terms:
- Fragment - Reusable sets of fields that can be included in multiple queries; saves time from needing to manually include the same fields over and over in many places
Further Reading:
GraphQL Fragments are the Best Match for UI Components by Samer Buna
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Up until this point, when we want to include a field in our response,
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we specify each field individually.
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Now this is fine for experimenting, but when building an actual project,
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there's a good chance we'll need to grab the same fields in multiple places.
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Fortunately GraphQL makes this possible with a concept called fragments.
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A fragment is simply a block of code
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that specifies a group of fields that you want to include in your response.
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To see how this works let's jump back in the Launchpad for an example.
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For this example, we'll be using the movie by ID in point again,
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aliased under movieOne and movieTwo.
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Just like in the last video, we'll start with our query declaration.
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Then we'll go ahead and write the first call the movieById,
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which will be aliased under movieOne.
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For this one, we'll use the movieId of movie_0,
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then in our response we'll include the id,
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title, tagline, and revenue fields.
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Now let's go ahead and repeat the same thing for movieTwo.
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Again, we've got the alias of movieTwo calling movieById.
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The movieId we'll use for this one is movie_1.
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And we'll go ahead and include those same fields again,
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id, title, tagline and revenue.
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Right now when we want to include the same fields for
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each movie, we have to manually type those fields out inside of each end point call.
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Now go ahead and run the query.
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As expected it works fine, we have both of our movies, but
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it was a little repetitive to type it all out.
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You can probably see how this could get tedious pretty quickly.
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This is exactly where fragments come in handy.
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To define a new fragment we'll start with the fragment key word.
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This fragment we'll call movie details.
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We then need to tell GraphQL which type this fragment can be used on
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using the on keyword followed by the Movie type.
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After that, it's just like any other query.
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Inside of the curly brackets we'll go ahead and
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copy paste the fields we used from our query above.
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Now let's modify those queries a bit.
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Inside of the curly brackets, go ahead and delete those fields.
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Now, instead of typing them all out, we can just include our new fragment.
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To do this type in three dots followed by the fragment name,
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which in this case is movieDetails.
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I did the same thing for movieTwo.
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Now go ahead and run that query.
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As you can see, it works like a charm.
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Using fragments when we need to retrieve the same information
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can save us quite a bit of time and quite a bit of typing.
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