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// Check $first/$last group accumulators. SERVER-3862
// $first/$last select first/last value for a group key from the previous pipeline.
t = db.jstests_aggregation_firstlast;
t.drop();
/** Check expected $first and $last result values. */
function assertFirstLast(expectedFirst, expectedLast, pipeline, expression) {
pipeline = pipeline || [];
expression = expression || '$b';
pipeline.push({$group: {_id: '$a', first: {$first: expression}, last: {$last: expression}}});
result = t.aggregate(pipeline).toArray();
for (var 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;
}
}
assert(false, "Expected group _id '1' missing.");
}
// One document.
t.save({a: 1, b: 1});
assertFirstLast(1, 1);
// Two documents.
t.save({a: 1, b: 2});
assertFirstLast(1, 2);
// Three documents.
t.save({a: 1, b: 3});
assertFirstLast(1, 3);
// Another 'a' key value does not affect outcome.
t.drop();
t.save({a: 3, b: 0});
t.save({a: 1, b: 1});
t.save({a: 1, b: 2});
t.save({a: 1, b: 3});
t.save({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, [{$sort: {b: -1}}]);
// Skip and limit affect the results seen.
t.drop();
t.save({a: 1, b: 1});
t.save({a: 1, b: 2});
t.save({a: 1, b: 3});
assertFirstLast(1, 2, [{$limit: 2}]);
assertFirstLast(2, 3, [{$skip: 1}, {$limit: 2}]);
assertFirstLast(2, 2, [{$skip: 1}, {$limit: 1}]);
// Mixed type values.
t.save({a: 1, b: 'foo'});
assertFirstLast(1, 'foo');
t.drop();
t.save({a: 1, b: 'bar'});
t.save({a: 1, b: true});
assertFirstLast('bar', true);
// Value null.
t.drop();
t.save({a: 1, b: null});
t.save({a: 1, b: 2});
assertFirstLast(null, 2);
t.drop();
t.save({a: 1, b: 2});
t.save({a: 1, b: null});
assertFirstLast(2, null);
t.drop();
t.save({a: 1, b: null});
t.save({a: 1, b: null});
assertFirstLast(null, null);
// Value missing.
t.drop();
t.save({a: 1});
t.save({a: 1, b: 2});
assertFirstLast(undefined, 2);
t.drop();
t.save({a: 1, b: 2});
t.save({a: 1});
assertFirstLast(2, undefined);
t.drop();
t.save({a: 1});
t.save({a: 1});
assertFirstLast(undefined, undefined);
// Dotted field.
t.drop();
t.save({a: 1, b: [{c: 1}, {c: 2}]});
t.save({a: 1, b: [{c: 6}, {}]});
assertFirstLast([1, 2], [6], [], '$b.c');
// Computed expressions.
t.drop();
t.save({a: 1, b: 1});
t.save({a: 1, b: 2});
assertFirstLast(1, 0, [], {$mod: ['$b', 2]});
assertFirstLast(0, 1, [], {$mod: [{$add: ['$b', 1]}, 2]});
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