Using `@key` in one subgraph and `@shareable` in another

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1

Suppose that there are two subgraphs, sub1 and sub2, defined for an Apollo Federation supergraph of version 2.0 or higher.
sub1’s schema contains:

#...
type MyType @shareable {
   idField: ID
   myField: String
}
#...

sub2’s schema contains:

#...
type MyType @key(fields:"idField") {
   idField: ID
   myField: String
}
#...

Is that a valid combination, or will it generate a schema composition error?

2

This is specific to Fed 2, but this is not a valid combination. @shareable and @key should not exist on the same type. They can be used for fields and other types, but not for Entities.

To understand more, see our What’s new in Federation 2 guide, but the short answer here is you need to first identity the type as an Entity using the @key directive. If the type can not be identified by some id or combination of fields with @key, then you should use @shareable instead.

But in your case you do have a key. In Fed 2 the fields marked as keys are automatically considered sharedable, all other fields that are shared across subgraph definitions need to be marked as shareable

 # Subgraph 1
type MyType @key(fields: "idField") {
   idField: ID
   myField: String @shareable
   foo: String
}

 # Subgraph 2
type MyType @key(fields: "idField") {
   idField: ID
   myField: String @shareable
   bar: String
}