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NODEJS-668: Handle empty pages in async pagination #419

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NODEJS-668: Handle empty pages in async pagination #419

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10 changes: 8 additions & 2 deletions lib/types/result-set.js
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Original file line number Diff line number Diff line change
Expand Up @@ -233,7 +233,7 @@ ResultSet.prototype[asyncIteratorSymbol] = function getAsyncGenerator() {
let pageState = this.rawPageState;
let rows = this.rows;

if (!rows || rows.length === 0) {
if (!pageState && (!rows || rows.length === 0)) {
return { next: () => Promise.resolve({ done: true }) };
}

Expand All @@ -257,7 +257,13 @@ ResultSet.prototype[asyncIteratorSymbol] = function getAsyncGenerator() {
return { done: false, value: rows[index++] };
}

return { done: true };
if (!pageState) {
return { done: true };
}

// We could reach this point if an empty page is returned.
// An empty page doesn't necessarily mean the end of the results.
return this.next();
}
};
};
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20 changes: 20 additions & 0 deletions test/unit/result-set-tests.js
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Expand Up @@ -135,6 +135,26 @@ describe('ResultSet', function () {
assert.ok(rs.nextPageAsync.firstCall.calledWithExactly(pageState));
});

it('should continue past empty pages', async () => {
const pageState = utils.allocBuffer(1);
const rs = new ResultSet( { rows: [ 100, 101, 102 ], meta: { pageState } });
const pages = [
[],
[],
[],
[ 103, 104, 105 ],
];
rs.nextPageAsync = sinon.spy(function () {
const rows = pages.shift();
return Promise.resolve({ rows: rows, rawPageState: pages.length > 0 ? pageState : undefined });
});

const result = await helper.asyncIteratorToArray(rs);
assert.deepEqual(result, [ 100, 101, 102, 103, 104, 105 ]);
assert.strictEqual(rs.nextPageAsync.callCount, 4);
assert.ok(rs.nextPageAsync.firstCall.calledWithExactly(pageState));
});

it('should reject when nextPageAsync rejects', async () => {
const rs = new ResultSet( { rows: [ 100 ], meta: { pageState: utils.allocBuffer(1)} });
const error = new Error('Test dummy error');
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