MongoDB

Question

假设我有以下名为mydata的集合：

{name: 'a', otherStuff: 'blah'},
{name: 'a', otherStuff: 'blah'},
{name: 'b', otherStuff: 'blah'},
{name: 'c', otherStuff: 'blah'},
{name: 'c', otherStuff: 'blah'},
{name: 'a', otherStuff: 'blah'}

如何获取唯一name值的总和？

例如，我正在寻找：

{name: 'a', count: 3},
{name: 'b', count: 1},
{name: 'c', count: 2}

我已尝试过搜索，但我只看到引用distinct命令的结果，该命令可以很好地挑出唯一值，但没有解释如何获得它们出现的次数的总和在集合中。

Answer 1

您应该使用聚合框架。

您的示例解决方案：

    db.collection.aggregate([{$group: {_id: "$name", count: {$sum: 1}}}, 
{$project: {name: "$_id", count: "$count", _id: 0}}]);