GraphQL how to do a JOIN request instead of many sequential request?

问题

I have two GraphQL type:

type Author {
  id: String!
  name: String!
}

type Book {
  id: String!
  author: Author!
  name: String!
}

In my database, it is implemented by a foreign key inside the books table:

table authors (pseudo code)

`id` INTEGER UNSIGNED
`name` STRING

table books (pseudo code)

`id` INTEGER UNSIGNED
`author_id` INTEGER UNSIGNED REFERENCE `authors.id`
`name` STRING

So when I resolve a GraphQL query like:

query allTheBooks {
  id
  name
  author {
    id
    name
  }
}

I would like to do only one SELECT SQL query like:

SELECT books.id, books.name, authors.id, authors.name
FROM books
LEFT JOIN authors ON authors.id = books.author_id

Instead of the current:

SELECT books.id, books.name, books.author_id
FROM books

SELECT authors.id, authors.name
FROM authors
WHERE author.id = [one the the books.author_id of the first SELECT]

SELECT authors.id, authors.name
FROM authors
WHERE author.id = [one the the books.author_id of the first SELECT]

[...]

Is there a way to know which "child fields" are queried in a GraphQL resolver ?

Thank you in advance for your answer !

回答1:

I just discovered that in the fourth parameter gived at the resolver, there where an array of the queried fields: info.fieldNodes[0].selectionSet.selections.

I didn't found any documentation about this, and I wonder what represent the fieldNodes array... (and dont like to access the first element that way without knowing it...).

The selections object contains an array like this:

[
  {
    kind: 'Field',
    alias: undefined,
    name: { kind: 'Name', value: 'id', loc: [Object] },
    arguments: [],
    directives: [],
    selectionSet: undefined,
    loc: { start: 36, end: 38 }
  },
  {
    [...]
  },
  ...
]

Here, the value: 'id' match the name of the queried field of the related author.

If I go a level deeped, the selectionSet: undefined becomes an object and the pattern repeat itself recursively...

来源：https://stackoverflow.com/questions/50548188/graphql-how-to-do-a-join-request-instead-of-many-sequential-request

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