Question

在使用$ size opration的例子中，作者狡猾地避免使用空格：

{ "_id" : 1, "item" : "ABC1", "description" : "product 1", colors: [ "blue", "black", "red" ] }
{ "_id" : 2, "item" : "ABC2", "description" : "product 2", colors: [ "purple" ] }
{ "_id" : 3, "item" : "XYZ1", "description" : "product 3", colors: [ ] }

请注意，所有字段都是引号，只有巧合的颜色不是：）

但如果我们有：

{ "_id" : 1, "item" : "ABC1", "description" : "product 1", "true colors": [ "blue", "black", "red" ] }
{ "_id" : 2, "item" : "ABC2", "description" : "product 2", "true colors": [ "purple" ] }
{ "_id" : 3, "item" : "XYZ1", "description" : "product 3", "true colors": [ ] }

我们如何编写查询：

numberOfColors: { $size: "$colors" }

更新

我找到了

numberOfColors: { $size: "$true colors" }

正常工作。但是＆＃34;点符号＆＃34 ;?我如何在这些字段中引用嵌套对象？

Answer 1

正如Alex在评论中提到的那样，给出了如下文档的嵌套对象

{ "_id" : 1, "item" : "ABC1", "description" : "product 1", 
      "all colors" : { "true colors" : [ "blue", "black", "red" ] } }
{ "_id" : 2, "item" : "ABC2", "description" : "product 2", 
      "all colors" : { "true colors" : [ "purple" ] } }

查询可能是

db.sp.aggregate([
    {$project: {item: 1, numberOfColor: {$size: '$all colors.true colors'}}}
]);

结果是

{ "_id" : 1, "item" : "ABC1", "numberOfColor" : 3 }
{ "_id" : 2, "item" : "ABC2", "numberOfColor" : 1 }

如何在MongoDB表达式中使用带空格的名称？

1 个答案: