在mongodb中使用$ redact和多个条件

Question

我有一个下面的mongo集合“test”，它没有在文档的顶层有“tags”字段。

{ 
    "_id" : 1, 
    "title" : "123 Department Report", 
    "year" : 2014, 
    "subsections" : [ 
     { 
      "subtitle" : "Section 1: Overview", 
      "tags" : "SI", 
      "content" : "Section 1: This is the content of section 1." 
     }, 
     { 
      "subtitle" : "Section 2: Analysis", 
      "tags" : "STLW", 
      "content" : "Section 2: This is the content of section 2." 
     }, 
     { 
      "subtitle" : "Section 3: Budgeting", 
      "tags" : "TK", 
      "content" : { 
       "text" : "Section 3: This is the content of section3.", 
       "tags" : "HCS" 
      } 
     } 
    ] 
} 

我的要求是选择只有“标签”值“STLW”的小节。 我正在运行下面的聚合查询。

db.test.aggregate([ 
    { $redact: { 
     $cond: {   
      if: { $or: [ {$ifNull: ['$tags', true]}, {$eq: [ "$tags" , 'STLW' ]} ] }, 
      then: "$$DESCEND", 
      else: "$$PRUNE" 
     } 
     } 
    } 
] 

然而上运行的查询，我让所有的子文档下面的输出：

{ 
    "_id" : 1, 
    "title" : "123 Department Report", 
    "year" : 2014, 
    "subsections" : [ 
     { 
      "subtitle" : "Section 1: Overview", 
      "tags" : "SI", 
      "content" : "Section 1: This is the content of section 1." 
     }, 
     { 
      "subtitle" : "Section 2: Analysis", 
      "tags" : "STLW", 
      "content" : "Section 2: This is the content of section 2." 
     }, 
     { 
      "subtitle" : "Section 3: Budgeting", 
      "tags" : "TK", 
      "content" : { 
       "text" : "Section 3: This is the content of section3.", 
       "tags" : "HCS" 
      } 
     } 
    ] 
} 

不过，我想下面的输出。

{ 
    "_id" : 1, 
    "title" : "123 Department Report", 
    "year" : 2014, 
    "subsections" : 
     { 
      "subtitle" : "Section 2: Analysis", 
      "tags" : "STLW", 
      "content" : "Section 2: This is the content of section 2." 
     } 
} 

任何人都可以帮助我实现这个目标吗？

感谢...........

Answer 1

这并不necesarily需要redact运营商，它可以通过使用unwind和match运营商来实现。以下调用...

db.test.aggregate([ 

    // find documents which have at least one subsection having a tag with the value "STLW" 
    {$match: {'subsections.tags': 'STLW'}}, 

    // unwind subsections so that the intermediate ouput contains one 'quasi doc' for each subsection 
    {$unwind: '$subsections'}, 

    // filter out any of the 'quasi docs' which do not have a tag with the value "STLW" 
    {$match: {'subsections.tags': 'STLW'}} 
]) 

...会产生这样的响应：

{ 
    "_id" : 1, 
    "title" : "123 Department Report", 
    "year" : 2014, 
    "subsections" : { 
     "subtitle" : "Section 2: Analysis", 
     "tags" : "STLW", 
     "content" : "Section 2: This is the content of section 2." 
    } 
}