GraphQL, Apollo Server Federated schema - graphql

Question

I get this error while querying:
"Cannot return null for non-nullable field Transaction.createdAt."
This is the query:
query getMyTransactions {
getMyTransactions {
id
createdAt
}
}
The schema for this query is:
extend type Transaction #key(fields: "id") {
id: ID! #external
}
type Query {
getMyTransactions: [Transaction!]!
}
And the other schema has Transaction type:
type Transaction #key(fields: "id") {
id: ID!
createdAt: String!
}
What's the problem?
EDIT: If I query for:
getMyTransactions {
id
}
Works ok I and get all the id of the query, but if I include another attribute the query fails.

Answer 1

In simple words - you declare createdAt type to be non-null value, but somewhere in your data createdAt is null.
createdAt: String!
! after the type name. This means that our server always expects to
return a non-null value for this field, and if it ends up getting a
null value that will actually trigger a GraphQL execution error,
letting the client know that something has gone wrong. GraphQl docs
Example
For this remote/local data (createdAt missing from the first object):
const Transaction = [
{
id: "1",
/* createdAt: "01/09/2020" */ /* missing from the data */
},
{
id: "2",
createdAt: "02/09/2020"
}
];
Executing query
query{
getMyTransactions {
id
createdAt
}
}
throw error:
"message": "Cannot return null for non-nullable field
Transaction.createdAt.",
To solve this:
Option 1: Add some resolver logic and/or add validation related to your required data.
Option 2: Remove the require from createdAt (return null allowed):