mongodb - 用计数器更新

Question

我有一个包含以下文件的fruit 集合:

{
  tag: "Apple",
  count: 3
},
{
  tag: "Banana",
  count: 2
}

我得到了带有标签和值的新文档。值1表示增加计数器，值-1表示减少计数器

{
  tag: "Coconut",
  value: 1
},
{
  tag: "Banana",
  count: -1
}

upsert 的结果应该是:

{
  tag: "Apple",
  count: 3
},
{
  tag: "Banana",
  count: 1      // previously 2, decrease counter by 1
},
{
  tag: "Coconut",
  count: 1      // Did not exist, so add and set counter to 1
}

此外，如果 count 减少到 0(或更少)，则从集合中删除该文档。所以如果我接下来得到这个:

{
  tag: "Apple",
  count: 1      
},
{
  tag: "Banana",
  count: -1      
}

下一个 upsert 的结果应该是

{
  tag: "Apple",    // previously 3, increase by 1
  count: 4
},
// {
//  tag: "Banana",
//  count: 0      // Remove from collection
// },
{
  tag: "Coconut",
  count: 1      
}

如何在 mongodb 中以简洁的方式实现这一点？

Answer 1

您可以使用 bulkWrite

$inc

db.myCollection.bulkWrite([
    {
        updateOne: { 
            filter: { tag: "Banana" } ,
            update: { $inc: { "count": -1 } }, 
            upsert : true 
        }
    },
    { 
        updateOne: { 
            filter: { tag: "Coconut" } ,
            update: { $inc: { "count": 1 } }, 
            upsert: true
        }
    },
    {
        deleteMany : { // delete records records if count is 0 or less
            filter : { count: { $lte: 0 } }
        }
    }
])