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GraphQL is a query language for APIs and a runtime for fulfilling those queries with your existing data. GraphQL queries always return predictable results.
GraphQL queries access not just the properties of one resource but also smoothly follow references between them. Access the full capabilities of your data from a single endpoint. Know exactly what data you can request from your API without leaving your editor, highlight potential issues before sending a query, and take advantage of improved code intelligence. Aging fields can be deprecated and hidden from tools.
GraphQL creates a uniform API across your entire application without being limited by a specific storage engine. Facebook's mobile apps have been powered by GraphQL since A GraphQL spec was open sourced in and is now available in many environments and used by teams of all sizes. Get Started Learn More. Get many resources in a single request GraphQL queries access not just the properties of one resource but also smoothly follow references between them.
Move faster with powerful developer tools Know exactly what data you can request from your API without leaving your editor, highlight potential issues before sending a query, and take advantage of improved code intelligence.
Bring your own data and code GraphQL creates a uniform API across your entire application without being limited by a specific storage engine.Fragments are a handy feature to help to improve the structure and reusability of your GraphQL code. A fragment is a collection of fields on a specific type. Now, when writing a query to access the address information of a user, we can use the following syntax to refer to the fragment and save the work to actually spell out the four fields:.
In GraphQL type definitions, each field can take zero or more arguments. Similar to arguments that are passed into functions in typed programming languages, each argument needs to have a name and a type.
We could now add an argument to the allUsers field that allows us to pass an argument to filter users and include only those above a certain age. We also specify a default value so that by default all users will be returned:. This olderThan argument can now be passed into the query using the following syntax:.
The only way to send a query like that would be to use aliases, i. In the result, the server would now name each User object according to the specified alias:.
In GraphQL, there are two different kinds of types. In every GraphQL schema, you can define your own scalar and object types. An often cited example for a custom scalar would be a Date type where the implementation needs to define how that type is validated, serialized, and deserialized. GraphQL allows you to define enumerations types short enumsa language feature to express the semantics of a type that has a fixed set of values.
We could thus define a type called Weekday to represent all the days of a week:. Note that technically enums are special kinds of scalar types. An interface can be used to describe a type in an abstract way.
It allows you to specify a set of fields that any concrete type, which implements this interface, needs to have. In many GraphQL schemas, every type is required to have an id field. Using interfaces, this requirement can be expressed by defining an interface with this field and then making sure that all custom types implement it:.
Union types can be used to express that a type should be either of a collection of other types. They are best understood by means of an example. Now, we could define a Person type to be the union of Adult and Child :.At its simplest, GraphQL is about asking for specific fields on objects. Let's start by looking at a very simple query and the result we get when we run it:. You can see immediately that the query has exactly the same shape as the result.
This is essential to GraphQL, because you always get back what you expect, and the server knows exactly what fields the client is asking for.
Oh, one more thing - the query above is interactive. That means you can change it as you like and see the new result. Try adding an appearsIn field to the hero object in the query, and see the new result. In the previous example, we just asked for the name of our hero which returned a String, but fields can also refer to Objects. In that case, you can make a sub-selection of fields for that object. GraphQL queries can traverse related objects and their fields, letting clients fetch lots of related data in one request, instead of making several roundtrips as one would need in a classic REST architecture.
Note that in this example, the friends field returns an array of items. GraphQL queries look the same for both single items or lists of items, however we know which one to expect based on what is indicated in the schema. If the only thing we could do was traverse objects and their fields, GraphQL would already be a very useful language for data fetching. But when you add the ability to pass arguments to fields, things get much more interesting.
You can even pass arguments into scalar fields, to implement data transformations once on the server, instead of on every client separately. Arguments can be of many different types. GraphQL comes with a default set of types, but a GraphQL server can also declare its own custom types, as long as they can be serialized into your transport format.Conditionally Rendering Buttons and Securing GraphQL Queries - Part 12
If you have a sharp eye, you may have noticed that, since the result object fields match the name of the field in the query but don't include arguments, you can't directly query for the same field with different arguments. That's why you need aliases - they let you rename the result of a field to anything you want. In the above example, the two hero fields would have conflicted, but since we can alias them to different names, we can get both results in one request.
Let's say we had a relatively complicated page in our app, which let us look at two heroes side by side, along with their friends.
You can imagine that such a query could quickly get complicated, because we would need to repeat the fields at least once - one for each side of the comparison. That's why GraphQL includes reusable units called fragments. Fragments let you construct sets of fields, and then include them in queries where you need to. Here's an example of how you could solve the above situation using fragments:. You can see how the above query would be pretty repetitive if the fields were repeated.
The concept of fragments is frequently used to split complicated application data requirements into smaller chunks, especially when you need to combine lots of UI components with different fragments into one initial data fetch.
It is possible for fragments to access variables declared in the query or mutation.It's often useful to ask a GraphQL schema for information about what queries it supports. GraphQL allows us to do so using the introspection system! For our Star Wars example, the file starWarsIntrospection-test.
Let's do so now, and ask what types are available. Now, let's try and figure out a good place to start exploring what queries are available.
When we designed our type system, we specified what type all queries would start at; let's ask the introspection system about that!
And that matches what we said in the type system section, that the Query type is where we will start! Note that the naming here was just by convention; we could have named our Query type anything else, and it still would have been returned here had we specified it was the starting type for queries.
Naming it Querythough, is a useful convention. It is often useful to examine one specific type. Let's take a look at the Droid type:. If we asked about Character instead we'd find that it is an interface:. It's useful for an object to know what fields are available, so let's ask the introspection system about Droid :.
If we queried for ofType on that field's type, we would find the ID type there, telling us that this is a non-null ID. We can query for ofType on those types, which will tell us what these are lists of.
Let's end with a feature of the introspection system particularly useful for tooling; let's ask the system for documentation! So we can access the documentation about the type system using introspection, and create documentation browsers, or rich IDE experiences.
This has just scratched the surface of the introspection system; we can query for enum values, what interfaces a type implements, and more. We can even introspect on the introspection system itself. The specification goes into more detail about this topic in the "Introspection" section, and the introspection file in GraphQL.
But is there an easy way for me to bring only, for example, users who are above 18 or any other age? This is possible-it would have to be different. Your query wouldn't be a valid GQL query. Something like this would:. It only showcases how to use features of GraphQL. If you tried example projects like for example star was api, those don't have any filtering built in.
Learn more. Asked 1 year, 6 months ago. Active 7 months ago. Viewed 6k times. Luis Coimbra Luis Coimbra 51 1 1 silver badge 7 7 bronze badges. Active Oldest Votes. Capaj Capaj 2, 2 2 gold badges 31 31 silver badges 42 42 bronze badges. You should send your age filter as a parameter.
Also it seems like that usersQuery ageLimit: Int, ageOperator: String : [users] and you should configure your resolver where statement with these operators. Berkay Kaan Berkay Kaan 8 8 bronze badges.
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Sign up using Facebook. Sign up using Email and Password. Post as a guest Name.On this page, you'll learn all you need to know about the GraphQL type system and how it describes what data can be queried.
Queries and Mutations
Since GraphQL can be used with any backend framework or programming language, we'll stay away from implementation-specific details and talk only about the concepts. If you've seen a GraphQL query before, you know that the GraphQL query language is basically about selecting fields on objects.
So, for example, in the following query:. Because the shape of a GraphQL query closely matches the result, you can predict what the query will return without knowing that much about the server. But it's useful to have an exact description of the data we can ask for - what fields can we select?
What kinds of objects might they return? What fields are available on those sub-objects? That's where the schema comes in. Every GraphQL service defines a set of types which completely describe the set of possible data you can query on that service. Then, when queries come in, they are validated and executed against that schema.
GraphQL services can be written in any language.
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The most basic components of a GraphQL schema are object types, which just represent a kind of object you can fetch from your service, and what fields it has. In the GraphQL schema language, we might represent it like this:. The language is pretty readable, but let's go over it so that we can have a shared vocabulary:. Every field on a GraphQL object type can have zero or more arguments, for example the length field below:.
Arguments can be either required or optional. When an argument is optional, we can define a default value - if the unit argument is not passed, it will be set to METER by default. Most types in your schema will just be normal object types, but there are two types that are special within a schema:.
Every GraphQL service has a query type and may or may not have a mutation type. These types are the same as a regular object type, but they are special because they define the entry point of every GraphQL query. So if you see a query that looks like:.
That means that the GraphQL service needs to have a Query type with hero and droid fields:. Mutations work in a similar way - you define fields on the Mutation type, and those are available as the root mutation fields you can call in your query.
It's important to remember that other than the special status of being the "entry point" into the schema, the Query and Mutation types are the same as any other GraphQL object type, and their fields work exactly the same way.
A GraphQL object type has a name and fields, but at some point those fields have to resolve to some concrete data. That's where the scalar types come in: they represent the leaves of the query. In the following query, the name and appearsIn fields will resolve to scalar types:. We know this because those fields don't have any sub-fields - they are the leaves of the query.Apollo Client 3.
Switch to the beta docs. Fetching data in a simple, predictable way is one of the core features of Apollo Client. You'll also learn how Apollo Client simplifies data management code by tracking error and loading states for you.
This article assumes you're familiar with building basic GraphQL queries. If you need a refresher, we recommend that you read this guide and practice running queries in GraphiQL. This article also assumes that you've already set up Apollo Client and have wrapped your React app in an ApolloProvider component. Read our getting started guide if you need help with either of those steps. To follow along with the examples below, open up our starter project and sample GraphQL server on CodeSandbox.
You can view the completed version of the app here. When your component renders, useQuery returns an object from Apollo Client that contains loadingerrorand data properties you can use to render your UI. Let's look at an example. Remember to wrap query strings in the gql function to parse them into query documents:.
GraphQL - Query
Next, we'll create a component named Dogs. As our query executes and the values of loadingerrorand data change, the Dogs component can intelligently render different UI elements according to the query's state:. When the user selects a dog breed from the populated dropdown, the selection is sent to the parent component via the provided onDogSelected function.
In the next step, we'll associate the dropdown with a more sophisticated query that uses GraphQL variables. Whenever Apollo Client fetches query results from your server, it automatically caches those results locally. This makes subsequent executions of the same query extremely fast. To see this caching in action, let's build a new component called DogPhoto. DogPhoto accepts a prop called breed that reflects the current value of the dropdown menu in our Dogs component:.
Notice that we're providing a configuration option variables to the useQuery hook this time. The variables option is an object that contains all of the variables we want to pass to our GraphQL query. In this case, we want to pass the currently selected breed from the dropdown.
Select bulldog from the dropdown to see its photo appear. Then switch to another breed, and then switch back to bulldog. You'll notice that the bulldog photo loads instantly the second time around.