Class BatchedArrayCursor<T>

Enables use with for await to deplete the cursor by asynchronously yielding every batch in the cursor's remaining result set.

Note: If the result set spans multiple batches, any remaining batches will only be fetched on demand. Depending on the cursor's TTL and the processing speed, this may result in the server discarding the cursor before it is fully depleted.

Example

const cursor = await db.query(aql`
  FOR user IN users
  FILTER user.isActive
  RETURN user
`);
for await (const users of cursor.batches) {
  for (const user of users) {
    console.log(user.email, user.isAdmin);
  }
}

Depletes the cursor, then returns an array containing all batches in the cursor's remaining result list.

Example

const cursor = await db.query(
  aql`FOR x IN 1..5 RETURN x`,
  { batchSize: 2 }
);
const result = await cursor.batches.all(); // [[1, 2], [3, 4], [5]]
console.log(cursor.hasNext); // false

Depletes the cursor by applying the callback function to each batch in the cursor's remaining result list. Returns an array containing the return values of callback for each batch, flattened to a depth of 1.

Note: If the result set spans multiple batches, any remaining batches will only be fetched on demand. Depending on the cursor's TTL and the processing speed, this may result in the server discarding the cursor before it is fully depleted.

See also: Array.prototype.flatMap.

Example

const cursor = await db.query(
  aql`FOR x IN 1..5 RETURN x`,
  { batchSize: 2 }
);
const squares = await cursor.batches.flatMap((currentBatch) => {
  return currentBatch.map((value) => value ** 2);
});
console.log(squares); // [1, 1, 2, 4, 3, 9, 4, 16, 5, 25]
console.log(cursor.hasNext); // false

Example

const cursor = await db.query(
  aql`FOR x IN 1..5 RETURN x`,
  { batchSize: 1 }
);
const odds = await cursor.batches.flatMap((currentBatch) => {
  if (currentBatch[0] % 2 === 0) {
    return []; // empty array flattens into nothing
  }
  return currentBatch;
});
console.logs(odds); // [1, 3, 5]

Advances the cursor by applying the callback function to each item in the cursor's remaining result list until the cursor is depleted or callback returns the exact value false. Returns a promise that evalues to true unless the function returned false.

Note: If the result set spans multiple batches, any remaining batches will only be fetched on demand. Depending on the cursor's TTL and the processing speed, this may result in the server discarding the cursor before it is fully depleted.

See also: Array.prototype.forEach.

Example

const cursor = await db.query(
  aql`FOR x IN 1..5 RETURN x`,
  { batchSize: 2 }
);
const result = await cursor.batches.forEach((currentBatch) => {
  for (const value of currentBatch) {
    console.log(value);
  }
});
console.log(result) // true
console.log(cursor.hasNext); // false

Example

const cursor = await db.query(
  aql`FOR x IN 1..5 RETURN x`,
  { batchSize: 2 }
);
const result = await cursor.batches.forEach((currentBatch) => {
  for (const value of currentBatch) {
    console.log(value);
  }
  return false; // stop after the first batch
});
console.log(result); // false
console.log(cursor.hasNext); // true

Drains the cursor and frees up associated database resources.

This method has no effect if all batches have already been consumed.

Example

const cursor1 = await db.query(aql`FOR x IN 1..5 RETURN x`);
console.log(cursor1.hasMore); // false
await cursor1.kill(); // no effect

const cursor2 = await db.query(
  aql`FOR x IN 1..5 RETURN x`,
  { batchSize: 2 }
);
console.log(cursor2.hasMore); // true
await cursor2.kill(); // cursor is depleted

Loads all remaining batches from the server.

Warning: This may impact memory use when working with very large query result sets.

Example

const cursor = await db.query(
  aql`FOR x IN 1..5 RETURN x`,
  { batchSize: 1 }
);
console.log(cursor.hasMore); // true
await cursor.batches.loadAll();
console.log(cursor.hasMore); // false
console.log(cursor.hasNext); // true
for await (const item of cursor) {
  console.log(item);
  // No server roundtrips necessary any more
}

Depletes the cursor by applying the callback function to each batch in the cursor's remaining result list. Returns an array containing the return values of callback for each batch.

Note: This creates an array of all return values, which may impact memory use when working with very large query result sets. Consider using forEach, reduce or flatMap instead.

See also: Array.prototype.map.

Example

const cursor = await db.query(
  aql`FOR x IN 1..5 RETURN x`,
  { batchSize: 2 }
);
const squares = await cursor.batches.map((currentBatch) => {
  return currentBatch.map((value) => value ** 2);
});
console.log(squares); // [[1, 4], [9, 16], [25]]
console.log(cursor.hasNext); // false

Advances the cursor and returns all remaining values in the cursor's current batch. If the current batch has already been exhausted, fetches the next batch from the server and returns it, or undefined if the cursor has been depleted.

Note: If the result set spans multiple batches, any remaining batches will only be fetched on demand. Depending on the cursor's TTL and the processing speed, this may result in the server discarding the cursor before it is fully depleted.

Example

const cursor = await db.query(
  aql`FOR i IN 1..10 RETURN i`,
  { batchSize: 5 }
);
const firstBatch = await cursor.batches.next(); // [1, 2, 3, 4, 5]
await cursor.next(); // 6
const lastBatch = await cursor.batches.next(); // [7, 8, 9, 10]
console.log(cursor.hasNext); // false

Depletes the cursor by applying the reducer function to each batch in the cursor's remaining result list. Returns the return value of reducer for the last batch.

Note: Most complex uses of the reduce method can be replaced with simpler code using forEach or the for await syntax.

Note: If the result set spans multiple batches, any remaining batches will only be fetched on demand. Depending on the cursor's TTL and the processing speed, this may result in the server discarding the cursor before it is fully depleted.

See also: Array.prototype.reduce.

Example

function largestValue(baseline, values) {
  return Math.max(baseline, ...values);
}
const cursor = await db.query(
  aql`FOR x IN 1..5 RETURN x`,
  { batchSize: 3 }
);
const result = await cursor.batches.reduce(largestValue, 0);
console.log(result); // 5
console.log(cursor.hasNext); // false
const emptyResult = await cursor.batches.reduce(largestValue, 0);
console.log(emptyResult); // 0

Example

// BAD! NEEDLESSLY COMPLEX!
const cursor = await db.query(
  aql`FOR x IN 1..5 RETURN x`,
  { batchSize: 1 }
);
const result = await cursor.reduce((accumulator, currentBatch) => {
  if (currentBatch[0] % 2 === 0) {
    accumulator.even.push(...currentBatch);
  } else {
    accumulator.odd.push(...currentBatch);
  }
  return accumulator;
}, { odd: [], even: [] });
console.log(result); // { odd: [1, 3, 5], even: [2, 4] }

// GOOD! MUCH SIMPLER!
const cursor = await db.query(aql`FOR x IN 1..5 RETURN x`);
const odd = [];
const even = [];
for await (const currentBatch of cursor) {
  if (currentBatch[0] % 2 === 0) {
    even.push(...currentBatch);
  } else {
    odd.push(...currentBatch);
  }
}
console.log({ odd, even }); // { odd: [1, 3, 5], even: [2, 4] }

Depletes the cursor by applying the reducer function to each batch in the cursor's remaining result list. Returns the return value of reducer for the last batch.

Note: If the result set spans multiple batches, any remaining batches will only be fetched on demand. Depending on the cursor's TTL and the processing speed, this may result in the server discarding the cursor before it is fully depleted.

See also: Array.prototype.reduce.

Example

function largestValue(values1, values2) {
  return [Math.max(...values1, ...values2)];
}
const cursor = await db.query(
  aql`FOR x IN 1..5 RETURN x`,
  { batchSize: 3 }
);
const result = await cursor.batches.reduce(largestValue);
console.log(result); // [5]
console.log(cursor.hasNext); // false