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Keep fetching on empty pages #46

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Oct 11, 2018
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Keep fetching on empty pages #46

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31 changes: 25 additions & 6 deletions src/ConnectionLoader.js
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,24 @@ const FIRST = '$$FIRST$$';

export default class ConnectionLoader {
constructor(singleConnectionHandler) {
const fetch = async ({ connection, options, ...props }) => {
const result = connection
? await singleConnectionHandler({ connection, options, ...props })
: await singleConnectionHandler({ options, ...props });

if (result.continuationToken && !result.items.length) {
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The returned items are not always in a property named "items". Bug 1436212 has some background on why this is hard.

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Every connection loader in taskcluster-web-server returns an items property (https://github.com/taskcluster/taskcluster-web-server/search?utf8=%E2%9C%93&q=items%3A&type=). I guess we can write tests to assert that each connection handler returns an object with an items fields.

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Oh, awesome. I didn't know these were results from a loader. One of the downsides of this heavily-functional style of programming is that it's not easy to follow control flow!

return fetch({
...props,
options: {
...options,
continuationToken: result.continuationToken,
},
});
}

return result;
};

return new DataLoader(connections =>
Promise.all(
connections.map(async ({ connection, ...props }) => {
Expand All @@ -22,22 +40,23 @@ export default class ConnectionLoader {
? { limit, continuationToken }
: { limit };
const result = connection
? await singleConnectionHandler({ ...props, connection, options })
: await singleConnectionHandler({ ...props, options });

return this.createPageConnection(result, {
? await fetch({ ...props, connection, options })
: await fetch({ ...props, options });
const pageConnection = this.createPageConnection(result, {
...connection,
...options,
});

return pageConnection;
})
)
);
}

createPageConnection({ continuationToken, items, ...props }, options) {
const pageInfo = {
hasNextPage: !!continuationToken,
hasPreviousPage: !!options.cursor && options.cursor !== FIRST,
hasNextPage: Boolean(continuationToken),
hasPreviousPage: Boolean(options.cursor) && options.cursor !== FIRST,
cursor: options.continuationToken || FIRST,
};

Expand Down