Is it possible to use inheritance with GraphQL input types?
Something like that (this, of course, doesn't work with input types):
interface UserInputInterface {
firstName: String
lastName: String
}
input UserInput implements UserInputInterface {
password: String!
}
input UserChangesInput implements UserInputInterface {
id: ID!
password: String
}
No, the spec does not allow input types to implement interfaces. And GraphQL type system in general does not define any form of inheritance (the extends keyword adds fields to an existing type, and isn't for inheritance). The spec is intentionally constrained to stay simple. This means that you're stuck repeating fields across input types.
That said, depending on the way you construct your schema, you could build some kind of type transformer that appends the common fields programmatically based on some meta-data, e.g. a directive.
Better yet, you might be able to solve your problem via composition (always keep composition over inheritance in mind).
E.g.
input Name {
firstName: String
lastName: String
}
input UserInput {
name: Name
password: String!
}
input UserChangesInput {
name: Name
id: ID!
password: String
}
The client now has to send an object a level deeper, but that doesn't sound like much of a price for avoiding big repeating chunks. It might actually be good for the client as well, as they can now have common logic for building names, regardless of the query/mutation using them.
In this example, where it's only 2 simple fields, this approach is an overkill, but in general - I'd say it's the way to go.
Starting with the June2018 stable version of the GraphQL spec, an Input Object type can extend another Input Object type:
Input object type extensions are used to represent an input object type which has been extended from some original input object type.
This isn't inheritance per se; you can only extend the base type, not create new types based on it:
extend input MyInput {
NewField: String
}
Note there is no name for the new type; the existing MyInput type is extended.
The JavaScript reference implementation has implemented Input Object extensions in GraphQL.js v14 (June 2018), though it's unclear how to actually pass the extended input fields to a query without getting an error.
For actual type inheritance, see the graphql-s2s library.
It's doable using a custom directive.
Code Summary
const typeDefs = gql`
directive #inherits(type: String!) on OBJECT
type Car {
manufacturer: String
color: String
}
type Tesla #inherits(type: "Car") {
manufacturer: String
papa: String
model: String
}
type Query {
tesla: Tesla
}
`;
const resolvers = {
Query: {
tesla: () => ({ model: 'S' }),
},
Car: {
manufacturer: () => 'Ford',
color: () => 'Orange',
},
Tesla: {
manufacturer: () => 'Tesla, Inc',
papa: () => 'Elon',
},
};
class InheritsDirective extends SchemaDirectiveVisitor {
visitObject(type) {
const fields = type.getFields();
const baseType = this.schema.getTypeMap()[this.args.type];
Object.entries(baseType.getFields()).forEach(([name, field]) => {
if (fields[name] === undefined) {
fields[name] = { ...field };
}
});
}
}
const schemaDirectives = {
inherits: InheritsDirective,
};
Query:
query {
tesla {
manufacturer
papa
color
model
}
}
Output:
{
"data": {
"tesla": {
"manufacturer": "Tesla, Inc",
"papa": "Elon",
"color": "Orange",
"model": "S",
}
}
}
Working example at https://github.com/jeanbmar/graphql-inherits.
If you came here looking for an explanation for the "implements", keyword, here it is:
An object type must be a super‐set of all interfaces it implements. The object type must include a field of the same name for every field defined in an interface.
(Excerpt taken from the June 2018 GraphQL spec.)
Here's an example
interface Foo {
id: ID!
foo: Int!
}
type Bar implements Foo #entity {
id: ID!;
foo: Int!;
bar: Int!;
}
So the Bar type doesn't inherit from the Foo interface, but it implements it. The former must include all the fields that are listed in the latter.
I think that this is a nice way to annotate types that should be like other types.
Related
I have a case where I have an interface, which has different type implementations defined in graphql. I may not be able to share the exact code. But the case looks something like:
interface Character {
name: String!
}
type Human implements Character {
name: String!
friends: [Character]
}
type Droid implements Character {
name: String!
material: String
}
There is query which returns either Human or Droid type in response.
Response may contain something like:
{
name: 'Human_01',
friends: []
__typename: 'Human'
}
or
{
name: 'Droid_01',
material: 'Aluminium'
__typename: 'Droid'
}
I am using Apollo Client 3 on client side for querying the data and have fragments for these like:
fragment Human on Human {
friends
}
fragment Droid on Droid {
material
}
fragment Character on Character {
name
...Human
...Droid
}
I am querying for the Character data as:
character {
...Character
}
Since, this is the case of interface, and as defined in the docs for Apollo client 3, we need to use possibleTypes in order to match the fragments in such cases. For caching purpose, I have defined InMemoryCache as:
new InMemoryCache({ possibleTypes: { Character: ['Human', 'Droid'] } })
The primary key field for a Character implementation is the name field, which I need to use in order to store its value in cache.
In Apollo client 3, it is mentioned to use typePolicies for defining keyFields for a type.
So, I need to ask as to whether I should define, type policy for both type implementations, specifying keyFields as name in both cases like:
new InMemoryCache({
possibleTypes: { Character: ['Human', 'Droid'] },
typePolicies: { Human: { keyFields: ['name'] }, Droid: { keyFields: ['name'] } }
});
In my example, I have provided only 2 such type implementations but there can be n number of type implementations corresponding to Character interface. So, in that case I will need to define keyFields as name in typePolicies for all the n type implementations.
So, does there exist any better way of implementing caching wrt these types of interface implementations ?
Any help would really be appreciated. Thanks!!!
Inheritance of type and field policies is coming in the next minor version of #apollo/client, v3.3!
You can try it out now by installing #apollo/client#3.3.0-beta.5.
To stay up to date on the progress of the v3.3 release, see this pull request.
I've read everything, understood no solution and concrete explanation (even here: Apollo / GraphQl - Type must be Input type)
I want to create an object System that contains Suns. So I do:
type System {
_id: ID
name: String! #unique
diameter: Int
suns: [Sun]
}
type Sun {
_id: ID
name: String
diameter: Int
}
type Mutation {
createSystem(name: String!, diameter: Int, suns: [Sun]): System!
}
And I write in playground:
mutation {
createSystem(name:"new system", suns: [{ name: "John" }]) {
name
suns
}
}
But I got a terminal error: "Error: The type of Mutation.createSystem(suns:) must be Input Type but got: [Sun]."
I understand that Sun isn't received as an object. How to declare it as an object?
Thank you very much for your answers
The GraphQL spec. does not allow using type (i.e. output type) as the input argument.It only allows the input arguments to be enum , Scalar and Input . That means you have to create a SunInput
input SunInput {
_id: ID
name: String
diameter: Int
}
You need to make a custom "Type" for sun with its own resolver.
suns: { type: new GraphQLList(SunType) } // just an example
mutation {
createSystem(name:"new system", suns-names: "John") {
name
}
}
It will have resolver that writes a new system to the database called new system that adds a sun of "SunType" to the a database collection with the name of "Sun" for example.
Using facebook's reference library, I found a way to hack generic types like this:
type PagedResource<Query, Item> = (pagedQuery: PagedQuery<Query>) => PagedResponse<Item>
interface PagedQuery<Query> {
query: Query;
take: number;
skip: number;
}
interface PagedResponse<Item> {
items: Array<Item>;
total: number;
}
function pagedResource({type, resolve, args}) {
return {
type: pagedType(type),
args: Object.assign(args, {
page: { type: new GraphQLNonNull(pageQueryType()) }
}),
resolve
};
function pageQueryType() {
return new GraphQLInputObjectType({
name: 'PageQuery',
fields: {
skip: { type: new GraphQLNonNull(GraphQLInt) },
take: { type: new GraphQLNonNull(GraphQLInt) }
}
});
}
function pagedType(type) {
return new GraphQLObjectType({
name: 'Paged' + type.toString(),
fields: {
items: { type: new GraphQLNonNull(new GraphQLList(type)) },
total: { type: new GraphQLNonNull(GraphQLInt) }
}
});
}
}
But I like how with Apollo Server I can declaratively create the schema. So question is, how do you guys go about creating generic-like types with the schema language?
You can create an interface or union to achieve a similar result. I think this article does a good job explaining how to implement interfaces and unions correctly. Your schema would look something like this:
type Query {
pagedQuery(page: PageInput!): PagedResult
}
input PageInput {
skip: Int!
take: Int!
}
type PagedResult {
items: [Pageable!]!
total: Int
}
# Regular type definitions for Bar, Foo, Baz types...
union Pageable = Bar | Foo | Baz
You also need to define a resolveType method for the union. With graphql-tools, this is done through the resolvers:
const resolvers = {
Query: { ... },
Pageable {
__resolveType: (obj) => {
// resolve logic here, needs to return a string specifying type
// i.e. if (obj.__typename == 'Foo') return 'Foo'
}
}
}
__resolveType takes the business object being resolved as its first argument (typically your raw DB result that you give GraphQL to resolve). You need to apply some logic here to figure out of all the different Pageable types, which one we're handling. With most ORMs, you can just add some kind of typename field to the model instance you're working with and just have resolveType return that.
Edit: As you pointed out, the downside to this approach is that the returned type in items is no longer transparent to the client -- the client would have to know what type is being returned and specify the fields for items within an inline fragment like ... on Foo. Of course, your clients will still have to have some idea about what type is being returned, otherwise they won't know what fields to request.
I imagine creating generics the way you want is impossible when generating a schema declaratively. To get your schema to work the same way it currently does, you would have to bite the bullet and define PagedFoo when you define Foo, define PagedBar when you define Bar and so on.
The only other alternative I can think of is to combine the two approaches. Create your "base" schema programatically. You would only need to define the paginated queries under the Root Query using your pagedResource function. You can then use printSchema from graphql/utilities to convert it to a String that can be concatenated with the rest of your type definitions. Within your type definitions, you can use the extend keyword to build on any of the types already declared in the base schema, like this:
extend Query {
nonPaginatedQuery: Result
}
If you go this route, you can skip passing a resolve function to pagedResource, or defining any resolvers on your programatically-defined types, and just utilize the resolvers object you normally pass to buildExecutableSchema.
I have a Apollo GraphQL server talking to an API returning responses with roughly the following structure:
{
"pagination": {
"page": 1,
// more stuff
},
sorting: {
// even more stuff
},
data: [ // Actual data ]
}
This structure is going to be shared across pretty much all responses from this API, that I'm using extensively. data is going to be an array most of the time, but can also be an object.
How can I write this in an efficient way, so that I don't have to repeat all these pagination and sorting fields on every data type in my schemas?
Thanks a lot!
I've sorted your problem by creating a lib called graphql-s2s. It enhances your schema by adding support for type inheritance, generic types and metadata. In your case, creating a generic type for your Paginated object could be a viable solution. Here is an example:
const { transpileSchema } = require('graphql-s2s')
const { makeExecutableSchema } = require('graphql-tools')
const schema = `
type Paged<T> {
data: [T]
cursor: ID
}
type Node {
id: ID!
creationDate: String
}
type Person inherits Node {
firstname: String!
middlename: String
lastname: String!
age: Int!
gender: String
}
type Teacher inherits Person {
title: String!
}
type Student inherits Person {
nickname: String!
questions: Paged<Question>
}
type Question inherits Node {
name: String!
text: String!
}
type Query {
students: Paged<Student>
teachers: Paged<Teacher>
}
`
const executableSchema = makeExecutableSchema({
typeDefs: [transpileSchema(schema)],
resolvers: resolver
})
I've written more details about this here (in Part II).
When you define your schema, you will end up abstracting out pagination, sorting, etc. as separate types. So the schema will look something like:
type Bar {
pagination: Pagination
sorting: SortingOptions
data: BarData # I'm an object
}
type Foo {
pagination: Pagination
sorting: SortingOptions
data: [FooData] # I'm an array
}
# more types similar to above
type Pagination {
page: Int
# more fields
}
type SortingOptions {
# more fields
}
type BarData {
# more fields
}
So you won't have to list each field within Pagination multiple times regardless. Each type that uses Pagination, however, will still need to specify it as a field -- there's no escaping that requirement.
Alternatively, you could set up a single Type to use for all your objects. In this case, the data field would be an Interface (Data), with FooData, BarData, etc. each implementing it. In your resolver for Data, you would define a __resolveType function to determine which kind of Data to return. You can pass in a typename variable with your query and then use that variable in the __resolveType function to return the correct type.
You can see a good example of Interface in action in the Apollo docs.
The downside to this latter approach is that you have to return either a single Data object or an Array of them -- you can't mix and match -- so you would probably have to change the structure of the returned object to make it work.
Is it possible to use inheritance with GraphQL input types?
Something like that (this, of course, doesn't work with input types):
interface UserInputInterface {
firstName: String
lastName: String
}
input UserInput implements UserInputInterface {
password: String!
}
input UserChangesInput implements UserInputInterface {
id: ID!
password: String
}
No, the spec does not allow input types to implement interfaces. And GraphQL type system in general does not define any form of inheritance (the extends keyword adds fields to an existing type, and isn't for inheritance). The spec is intentionally constrained to stay simple. This means that you're stuck repeating fields across input types.
That said, depending on the way you construct your schema, you could build some kind of type transformer that appends the common fields programmatically based on some meta-data, e.g. a directive. Here's one such implementation.
Better yet, you might be able to solve your problem via composition (always keep composition over inheritance in mind).
E.g.
input Name {
firstName: String
lastName: String
}
input UserInput {
name: Name
password: String!
}
input UserChangesInput {
name: Name
id: ID!
password: String
}
The client now has to send an object a level deeper, but that doesn't sound like much of a price for avoiding big repeating chunks. It might actually be good for the client as well, as they can now have common logic for building names, regardless of the query/mutation using them.
In this example, where it's only 2 simple fields, this approach is an overkill, but in general - I'd say it's the way to go.
Starting with the June2018 stable version of the GraphQL spec, an Input Object type can extend another Input Object type:
Input object type extensions are used to represent an input object type which has been extended from some original input object type.
This isn't inheritance per se; you can only extend the base type, not create new types based on it:
extend input MyInput {
NewField: String
}
Note there is no name for the new type; the existing MyInput type is extended.
The JavaScript reference implementation has implemented Input Object extensions in GraphQL.js v14 (June 2018), though it's unclear how to actually pass the extended input fields to a query without getting an error.
For actual type inheritance, see the graphql-s2s library.
It's doable using a custom directive.
Code Summary
const typeDefs = gql`
directive #inherits(type: String!) on OBJECT
type Car {
manufacturer: String
color: String
}
type Tesla #inherits(type: "Car") {
manufacturer: String
papa: String
model: String
}
type Query {
tesla: Tesla
}
`;
const resolvers = {
Query: {
tesla: () => ({ model: 'S' }),
},
Car: {
manufacturer: () => 'Ford',
color: () => 'Orange',
},
Tesla: {
manufacturer: () => 'Tesla, Inc',
papa: () => 'Elon',
},
};
class InheritsDirective extends SchemaDirectiveVisitor {
visitObject(type) {
const fields = type.getFields();
const baseType = this.schema.getTypeMap()[this.args.type];
Object.entries(baseType.getFields()).forEach(([name, field]) => {
if (fields[name] === undefined) {
fields[name] = { ...field };
}
});
}
}
const schemaDirectives = {
inherits: InheritsDirective,
};
Query:
query {
tesla {
manufacturer
papa
color
model
}
}
Output:
{
"data": {
"tesla": {
"manufacturer": "Tesla, Inc",
"papa": "Elon",
"color": "Orange",
"model": "S",
}
}
}
Working example at https://github.com/jeanbmar/graphql-inherits.
If you came here looking for an explanation for the "implements", keyword, here it is:
An object type must be a super‐set of all interfaces it implements. The object type must include a field of the same name for every field defined in an interface.
(Excerpt taken from the June 2018 GraphQL spec.)
Here's an example
interface Foo {
id: ID!
foo: Int!
}
type Bar implements Foo #entity {
id: ID!;
foo: Int!;
bar: Int!;
}
So the Bar type doesn't inherit from the Foo interface, but it implements it. The former must include all the fields that are listed in the latter.
I think that this is a nice way to annotate types that should be like other types.