GraphQLDependency.load() method

Loads everything the request asked for beneath this type and attaches it to the result, in as few bulk calls as the graph allows.

Signature:

load(source: ResultType, context: any, fields: any): Promise<ResultType>;

Parameters

Returns:

Promise<ResultType>

source, with the requested dependencies attached

Remarks

This is the one runtime call. Everything else on this class is start-up declaration; here those declarations meet an actual query. Invoke it from a top-level resolver, after the initial service call, and hand it the fields the client asked for.

What it does, in order: scan the requested fields for types that have a dependency description; merge every request for the same type into one minimal field set; run the initializers and bulk loaders in dependency order, level by level and concurrently within a level; attach each loaded object to its parents; and return the result.

Two things to be aware of, both of which follow from matching by id. fields is mutated: id is added at every level of the map, since without it nothing can be attached. And source is mutated too — the dependency fields are written onto the very objects that were passed in, and the return value is that same object rather than a copy. Loaded children are shared by reference between the parents that match them, so a result graph stays cheap even when many parents point at the same child.

A falsy fields short-circuits: nothing is requested, so source comes back untouched. source may be a single object or an array of them.

Example

async function user(
    source: any,
    args: any,
    context: any,
    info: GraphQLResolveInfo,
) {
    const fields = fieldsMap(info);
    const data = await context.user.listUser(args);

    // fills in every dependent structure the query touched
    return Dependency(UserType).load(data, context, fields);
}

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