Question

我有一个mongo集合，其中包含以下文档：

{
    _id: ObjectId("5c7ba3c0e30e6132f8b0c4ef"),
    replies: [
        {
            _id: ObjectId("5c7ba3c0e30e6132f8b0c4ef"),
            status: 'rejected'
        }
    ]
}

我想获得所有已批准状态的答复，因此我进行以下查询：

Collection.find({'replies.status': 'approved'})

，上面的文档仍显示在结果中。我在做什么错了？

Answer 1

这是对查询过程的常见误解。我怀疑您的其中一个文档看起来像这样：

{
    "_id" : 0,
  "replies" : [
  { "_id" : "R0", status: "rejected"}
  ,{ "_id" : "R1", status: "approved"}
  ]
}

问题在于，在数组上执行find会匹配数组条目中至少一个匹配的任何文档；它不会将结果过滤为仅这些条目。这是两种方法。鉴于此数据设置：

var r =
[
{
    "_id" : 0,
  "replies" : [
  { "_id" : "R0", status: "rejected"}
  ,{ "_id" : "R1", status: "approved"}
  ]
}
,{
    "_id" : 1,
  "replies" : [
  { "_id" : "R2", status: "rejected"}
  ,{ "_id" : "R3", status: "rejected"}
  ]
}
,{
    "_id" : 2,
  "replies" : [
  { "_id" : "R4", status: "rejected"}
  ,{ "_id" : "R5", status: "approved"}
  ]
}
 ];

方法1：简单且嵌入式数组很小（条目数不超过100或1000。

db.foo.aggregate([
// This will find all docs where ANY of the replies array has AT LEAST ONE      
// entry "approved."   It will NOT filter just those.                           
{$match: {"replies.status": "approved"}}

// Now that we have them, unwind and "refilter"                                 
,{$unwind: "$replies"}

,{$match: {"replies.status": "approved"}}
   ]);

{ "_id" : 0, "replies" : { "_id" : "R1", "status" : "approved" } }
{ "_id" : 2, "replies" : { "_id" : "R5", "status" : "approved" } }

方法2：如果数组非常大，请使用$filter，使用$unwind会创建1000个文档。这种方法在保留原始文档的结构中也很有用：

db.foo.aggregate([
// This will find all docs where ANY of the replies array has AT LEAST ONE      
// entry "approved."   It will NOT filter just those.                           
{$match: {"replies.status": "approved"}}

// To avoid $unwind, directly filter just "approved" and reset the replies      
// field back into the parent doc:                                              
,{$addFields: {replies: {$filter: {
                input: "$replies",
                as: "zz",
                cond: { $eq: [ "$$zz.status", "approved" ] }
            }}
    }}

   ]);

/*                                                                              
{                                                                               
    "_id" : 0,                                                                  
        "replies" : [                                                           
                     {                                                          
                         "_id" : "R1",                                          
                             "status" : "approved"                              
                             }                                                  
                     ]                                                          
        }                                                                       
{                                                                               
    "_id" : 2,                                                                  
        "replies" : [                                                           
                     {                                                          
                         "_id" : "R5",                                          
                             "status" : "approved"                              
                             }                                                  
                     ]                                                          
        }                                                                       
}

如何在mongodb中查询对象数组的字段？

1 个答案: