在查找/聚合之后填写具有默认值的文档

I have a collection:

我有一个集合:

{ "name" : "A", "value" : 1, "date" : ISODate("2014-01-01T00:00:00.000Z") }{ "name" : "B", "value" : 7, "date" : ISODate("2014-01-01T00:00:00.000Z") }{ "name" : "A", "value" : 3, "date" : ISODate("2014-01-02T00:00:00.000Z") }{ "name" : "B", "value" : 8, "date" : ISODate("2014-01-02T00:00:00.000Z") }{ "name" : "B", "value" : 8, "date" : ISODate("2014-01-03T00:00:00.000Z") }{ "name" : "A", "value" : 5, "date" : ISODate("2014-01-04T00:00:00.000Z") }{ "name" : "A", "value" : 4, "date" : ISODate("2014-01-05T00:00:00.000Z") }{ "name" : "A"