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/**
* Tests the $first and $last accumulators in $group.
*/
(function() {
'use strict';
const coll = db.jstests_aggregation_firstlast;
coll.drop();
/** Check expected $first and $last result values. */
function assertFirstLast(expectedFirst, expectedLast, stages, expression) {
let pipeline = [{$sort: {_id: 1}}];
if (stages) {
pipeline = pipeline.concat(stages);
}
expression = expression || '$b';
pipeline.push(
{$group: {_id: '$a', first: {$first: expression}, last: {$last: expression}}});
const result = coll.aggregate(pipeline).toArray();
for (let i = 0; i < result.length; ++i) {
if (result[i]._id === 1) {
// Check results for group _id 1.
assert.eq(expectedFirst, result[i].first);
assert.eq(expectedLast, result[i].last);
return;
}
}
throw new Error('Expected $group _id "1" is missing');
}
// One document.
assert.writeOK(coll.insert({a: 1, b: 1}));
assertFirstLast(1, 1);
// Two documents.
assert.writeOK(coll.insert({a: 1, b: 2}));
assertFirstLast(1, 2);
// Three documents.
assert.writeOK(coll.insert({a: 1, b: 3}));
assertFirstLast(1, 3);
// Another 'a' key value does not affect outcome.
assert(coll.drop());
assert.writeOK(coll.insert({a: 3, b: 0}));
assert.writeOK(coll.insert({a: 1, b: 1}));
assert.writeOK(coll.insert({a: 1, b: 2}));
assert.writeOK(coll.insert({a: 1, b: 3}));
assert.writeOK(coll.insert({a: 2, b: 0}));
assertFirstLast(1, 3);
// Additional pipeline stages do not affect outcome if order is maintained.
assertFirstLast(1, 3, [{$project: {x: '$a', y: '$b'}}, {$project: {a: '$x', b: '$y'}}]);
// Additional pipeline stages affect outcome if order is modified.
assertFirstLast(3, 1, [{$sort: {b: -1}}]);
// Skip and limit affect the results seen.
assert(coll.drop());
assert.writeOK(coll.insert({a: 1, b: 1}));
assert.writeOK(coll.insert({a: 1, b: 2}));
assert.writeOK(coll.insert({a: 1, b: 3}));
assertFirstLast(1, 2, [{$limit: 2}]);
assertFirstLast(2, 3, [{$skip: 1}, {$limit: 2}]);
assertFirstLast(2, 2, [{$skip: 1}, {$limit: 1}]);
// Mixed type values.
assert.writeOK(coll.insert({a: 1, b: 'foo'}));
assertFirstLast(1, 'foo');
assert(coll.drop());
assert.writeOK(coll.insert({a: 1, b: 'bar'}));
assert.writeOK(coll.insert({a: 1, b: true}));
assertFirstLast('bar', true);
// Value null.
assert(coll.drop());
assert.writeOK(coll.insert({a: 1, b: null}));
assert.writeOK(coll.insert({a: 1, b: 2}));
assertFirstLast(null, 2);
assert(coll.drop());
assert.writeOK(coll.insert({a: 1, b: 2}));
assert.writeOK(coll.insert({a: 1, b: null}));
assertFirstLast(2, null);
assert(coll.drop());
assert.writeOK(coll.insert({a: 1, b: null}));
assert.writeOK(coll.insert({a: 1, b: null}));
assertFirstLast(null, null);
// Value missing.
assert(coll.drop());
assert.writeOK(coll.insert({a: 1}));
assert.writeOK(coll.insert({a: 1, b: 2}));
assertFirstLast(undefined, 2);
assert(coll.drop());
assert.writeOK(coll.insert({a: 1, b: 2}));
assert.writeOK(coll.insert({a: 1}));
assertFirstLast(2, undefined);
assert(coll.drop());
assert.writeOK(coll.insert({a: 1}));
assert.writeOK(coll.insert({a: 1}));
assertFirstLast(undefined, undefined);
// Dotted field.
assert(coll.drop());
assert.writeOK(coll.insert({a: 1, b: [{c: 1}, {c: 2}]}));
assert.writeOK(coll.insert({a: 1, b: [{c: 6}, {}]}));
assertFirstLast([1, 2], [6], [], '$b.c');
// Computed expressions.
assert(coll.drop());
assert.writeOK(coll.insert({a: 1, b: 1}));
assert.writeOK(coll.insert({a: 1, b: 2}));
assertFirstLast(1, 0, [], {$mod: ['$b', 2]});
assertFirstLast(0, 1, [], {$mod: [{$add: ['$b', 1]}, 2]});
}());
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