Using graphql-tools to mock a GraphQL server seems broken - graphql

Question

I've followed the documentation about using graphql-tools to mock a GraphQL server, however this throws an error for custom types, such as:
Expected a value of type "JSON" but received: [object Object]
The graphql-tools documentation about mocking explicitly states that they support custom types, and even provide an example of using the GraphQLJSON custom type from the graphql-type-json project.
I've provided a demo of a solution on github which uses graphql-tools to successfully mock a GraphQL server, but this relies on monkey-patching the built schema:
// Here we Monkey-patch the schema, as otherwise it will fall back
// to the default serialize which simply returns null.
schema._typeMap.JSON._scalarConfig.serialize = () => {
return { result: 'mocking JSON monkey-patched' }
}
schema._typeMap.MyCustomScalar._scalarConfig.serialize = () => {
return mocks.MyCustomScalar()
}
Possibly I'm doing something wrong in my demo, but without the monkey-patched code above I get the error regarding custom types mentioned above.
Does anyone have a better solution than my demo, or any clues as to what I might be doing wrong, and how I can change the code so that the demo works without monkey-patching the schema?
The relevant code in the demo index.js is as follows:
/*
** As per:
** http://dev.apollodata.com/tools/graphql-tools/mocking.html
** Note that there are references on the web to graphql-tools.mockServer,
** but these seem to be out of date.
*/
const { graphql, GraphQLScalarType } = require('graphql');
const { makeExecutableSchema, addMockFunctionsToSchema } = require('graphql-tools');
const GraphQLJSON = require('graphql-type-json');
const myCustomScalarType = new GraphQLScalarType({
name: 'MyCustomScalar',
description: 'Description of my custom scalar type',
serialize(value) {
let result;
// Implement your own behavior here by setting the 'result' variable
result = value || "I am the results of myCustomScalarType.serialize";
return result;
},
parseValue(value) {
let result;
// Implement your own behavior here by setting the 'result' variable
result = value || "I am the results of myCustomScalarType.parseValue";
return result;
},
parseLiteral(ast) {
switch (ast.kind) {
// Implement your own behavior here by returning what suits your needs
// depending on ast.kind
}
}
});
const schemaString = `
scalar MyCustomScalar
scalar JSON
type Foo {
aField: MyCustomScalar
bField: JSON
cField: String
}
type Query {
foo: Foo
}
`;
const resolverFunctions = {
Query: {
foo: {
aField: () => {
return 'I am the result of resolverFunctions.Query.foo.aField'
},
bField: () => ({ result: 'of resolverFunctions.Query.foo.bField' }),
cField: () => {
return 'I am the result of resolverFunctions.Query.foo.cField'
}
},
},
};
const mocks = {
Foo: () => ({
// aField: () => mocks.MyCustomScalar(),
// bField: () => ({ result: 'of mocks.foo.bField' }),
cField: () => {
return 'I am the result of mocks.foo.cField'
}
}),
cField: () => {
return 'mocking cField'
},
MyCustomScalar: () => {
return 'mocking MyCustomScalar'
},
JSON: () => {
return { result: 'mocking JSON'}
}
}
const query = `
{
foo {
aField
bField
cField
}
}
`;
const schema = makeExecutableSchema({
typeDefs: schemaString,
resolvers: resolverFunctions
})
addMockFunctionsToSchema({
schema,
mocks
});
// Here we Monkey-patch the schema, as otherwise it will fall back
// to the default serialize which simply returns null.
schema._typeMap.JSON._scalarConfig.serialize = () => {
return { result: 'mocking JSON monkey-patched' }
}
schema._typeMap.MyCustomScalar._scalarConfig.serialize = () => {
return mocks.MyCustomScalar()
}
graphql(schema, query).then((result) => console.log('Got result', JSON.stringify(result, null, 4)));

Answer 1

I and a few others are seeing a similar issue with live data sources (in my case MongoDB/Mongoose). I suspect it is something internal to the graphql-tools makeExecutableSchema and the way it ingests text-based schemas with custom types.
Here's another post on the issue: How to use graphql-type-json package with GraphQl
I haven't tried the suggestion to build the schema in code, so can't confirm whether it works or not.
My current workaround is to stringify the JSON fields (in the connector) when serving them to the client (and parsing on the client side) and vice-versa. A little clunky but I'm not really using GraphQL to query and/or selectively extract the properties within the JSON object. This wouldn't be optimal for large JSON objects I suspect.

Answer 2

If anyone else comes here from Google results, the solution for me was to add the JSON resolver as parameter to the makeExecutableSchema call. It's described here:
https://github.com/apollographql/apollo-test-utils/issues/28#issuecomment-377794825
That made the mocking work for me.