Nested partial types in Typescript

Question

I'm trying to type partial objects from GraphQL queries. In particular, I'm having trouble with an object similar to as follows ...

// Typescript types

interface Foo {
  bar: Bar
}

interface Bar {
  a: number,
  b: number
}

// GrapQL query

foo {
  bar {
    a
    // Note missing 'b' property
  }
}

When I pcome to type this response I can use Pick on the Bar property, but this then violates Foos declaration. I could create an entire new type but in my actual axample both Foo and Bar are complex objects - is there an easier way to type the result? How do people normally type GraphQL results?

asking for one field doesn't mean 2nd doesn't exist

xadm
– xadm

2021-06-07 08:47:28 +00:00
Commented Jun 7, 2021 at 8:47 — xadm
– xadm, Commented Jun 7, 2021 at 8:47

Juraj Kocan · Accepted Answer · 2021-06-07 08:47:25Z

1

i would recommend to use some existing package that can generate that types for you. eg gql code generator

otherwise easy way to avoid this type is to create partial types within whole object tree

interface Foo {
    bar: Bar;
}

interface Bar {
    a: number;
    b: number;
}

type partial<T extends object> = {
    [K in keyof T]?: T[K] extends object ? partial<T[K]> : T[K] 
}

const partialFoo: partial<Foo> = {
    bar: {
        a: 1
    }
}

answered Jun 7, 2021 at 8:47

Juraj Kocan

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