The variable can be a global query variable, a local variable declared via or a literal (e.g. Note that when passing to a fragment, we can pass a literal value or pass another variable. Since fragments with only locally-scoped variables do not use global variables, they do not suffer from this issue. This can also lead to awkward situations, like having multiple versions of the "same" variable, such as $showDetailedResults and $showDetails. Since a fragment can potentially be accessible from many queries, modifying a fragment that uses global variables can require changes to many query definitions. If you want to auto-generate the introspection result, there's a tool called GraphQL Code Generator that does it.Locally-scoped variables also make it easier to reuse a fragment from another query.Ī query definition must list all variables that are used by any nested fragments, including in recursively-nested fragments. You can automate this or set this as a script to run at build time. Query your server / schema to obtain the necessary information about unions and interfaces and write it to a file.To set it up, follow the three steps below: We recommend setting up a build step that extracts the necessary information from the schema into a JSON file, where it can be imported from when constructing the fragment matcher. If there are any changes related to union or interface types in your schema, you will have to update the fragment matcher accordingly. To support result validation and accurate fragment matching on unions and interfaces, a special fragment matcher called the IntrospectionFragmentMatcher can be used. The section below explains how to pass the necessary schema knowledge to the Apollo Client cache so unions and interfaces can be accurately matched and results validated before writing them into the store. The IntrospectionFragmentMatcher is the solution for working with unions/interfaces, and is explained in more detail below. Apollo Client will let you know this with a console warning (in development), if it attempts to use the default heuristic fragment matcher with unions/interfaces. Also, the heuristic fragment matcher will not work accurately when using fragment s with unions or interfaces. This works in most cases, but it also means that Apollo Client cannot check the server response for you, and it cannot tell you when you're manually writing invalid data into the store using update, updateQuery, writeQuery, etc. By default, Apollo Client's cache will use a heuristic fragment matcher, which assumes that a fragment matched if the result included all the field s in its selection set, and didn't match when any field was missing. Both Jedi and Droid are possible concrete types of Character, but on the client there is no way to know that without having some information about the schema. In the query above, all_people returns a result of type Character. To do so, we can simply share a fragment describing the field s we need for a comment: This way we can be sure that we render consistent comment objects as the data changes. For instance, in GitHunt on the comments page, we want to fetch the same field s after posting a comment as we originally query. Gatsby uses GraphQL to enable page and static query queries to declare what data they and their sub-components need. Using a special syntax, you describe the data you want in your component and then that data is given to you. If you’re familiar with SQL, it works in a very similar way. The most straightforward use of fragment s is to reuse parts of queries (or mutation s or subscriptions) in various parts of your application. GraphQL is a q uery l anguage (the QL part of its name). In this document we'll outline patterns to do both we'll also make use of utilities in the graphql-anywhere and graphql-tag packages which aim to help us, especially with the second problem. Breaking your queries up to allow you to co-locate field access with the places they are used.Sharing fields between multiple queries, mutations or subscriptions.There are two principal uses for fragment s in Apollo: In this case, people is of type Person and we want to select the firstName and lastName field s from people(id: "7"). It's important to note that the component after the on clause is designated for the type we are selecting from.
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