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const productLoader = new DataLoader(getBackendProducts); | |
const resolvers = { | |
Query: { | |
async product(_, { id }, __, info) { | |
const fields = getFields(info); | |
const backendFields = getBackendFields(fields, dependencyMap); | |
const backendResponse = await productLoader.load({ id, fields: backendFields }); | |
const schemaResponse = getSchemaResponse(backendResponse, fields, transformerMap); | |
return schemaResponse; | |
} | |
} | |
}; | |
const dependencyMap = { | |
name: ["title"], | |
price: ["price.currency", "price.amount"], | |
stock: ["stock_availability"], | |
}; | |
const transformerMap = { | |
name: resp => resp.title, | |
price: resp => `${resp.currency} ${resp.amount}`, | |
stock: resp => resp.stock_availability, | |
}; | |
function getFields(info) { | |
return info | |
.fieldNodes[0] // TODO: handle all field nodes in other fragments | |
.selectionSet | |
.selections | |
.map( | |
selection => // TODO: handle fragments | |
selection.name.value | |
); | |
} | |
function getBackendFields(schemaFields, dependencyMap) { | |
// Set helps in deduping | |
const backendFields = new Set( | |
schemaFields | |
.map(field => dependencyMap[field]) | |
.reduce((acc, field) => [...acc, ...field], []) | |
); | |
return backendFields; | |
} | |
async function getBackendProducts(inputs) { | |
const {ids, mergedFields} = mergeInputs(inputs); | |
const products = await fetch(`/products?ids=${ids.join(",")}&fields=${mergedFields}`); | |
return products; | |
} | |
function mergeInputs(inputs) { | |
const ids = []; | |
const fields = new Set(); | |
for (const input of inputs) { | |
ids.push(input.ids); | |
for (const field of input.fields) { | |
fields.add(field); | |
} | |
} | |
return { | |
ids, | |
mergedFields: [...fields].join(",") | |
}; | |
} | |
function getSchemaResponse( | |
backendResponse, | |
transformerMap, | |
schemaFields | |
) { | |
const schemaResponse = {}; | |
for (const field of schemaFields) { | |
schemaResponse[field] = transformerMap[field](backendResponse); | |
} | |
return schemaResponse; | |
} |
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@eelayoubi Completely true. If you have a single data source for the root field, this will just work. The problem we had was a bit more complicated - We have multiple data sources for a field like
product
- the data source is picked based on theid
. Each data source has a different dependency map and a transformer map. A single resolver for a field would work if there is only one of such things.I'm looking at further ways to ease this process of writing code.