how to search through a mongodb collection for dictionary keys nested in array

Question

i have some data in a mongodb database collection (i know which collection so im only looking through the collection ) with documents that looks like this:

{ "_id" : ObjectId("52a93577dadf672b96062729"), 
  "owner" : "user1", 
  "files" : [  
              {  "IyzkmGh4YGD61Tc3TJjaEY17hDldH" : "rws" } 
            ] 
}
{ "_id" : ObjectId("52a92f43dadf672b96062725"), 
  "owner" : "user2", 
  "files" : [    
              {       "tUI7RtvpHZklptvHVYssamlgHP6xs" : "rws" },
              {       "RsxRDQdXmHgmSLhMJ8tPxILxarruK" : "rws" },    
              {       "IyzkmGh4YGD61Tc3TJjaEY17hDldH" : "rw" },      
              {       "YA4to7HaB5Gm6JuZrwYrFit7IzvgO" : "rws" } 
           ] 
}

im trying to think of a way to find all documents that have a particular dictionary key in the array of files within them

like for the sample data if i search using the string IyzkmGh4YGD61Tc3TJjaEY17hDldH, id like both samples to match since they both have a dictionary with that key in their list of files, how would i perform this query? im working with the python motor to access mongodb. The reason is i'd like to delete these entries when files they represent are no longer in existence, The schema is at my disposal, i could change it to make this kind of search more sane,

JohnnyHK · Accepted Answer · 2013-12-18 21:01:34Z

11

You can use dot notation in your query keys to do this, using the $exists operator to just check for existence:

db.test.find({'files.IyzkmGh4YGD61Tc3TJjaEY17hDldH': {'$exists': 1}})

To find all docs that contain those files and remove them:

db.test.update(
    {'files.IyzkmGh4YGD61Tc3TJjaEY17hDldH': {'$exists': 1}},
    {'$pull': {'files': {'IyzkmGh4YGD61Tc3TJjaEY17hDldH': {'$exists': 1}}}},
    multi=True)

edited Dec 18, 2013 at 21:01

answered Dec 18, 2013 at 18:03

JohnnyHK

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3 Comments

mike Over a year ago

any idea how i would delete the entry(s)? i tried different variants of this and it did not work: db.user_data.update({'projects.IyzkmGh4YGD61Tc3TJjaEY17hDldH': {'$exists': 1}},{ $pull : { 'projects' : 'IyzkmGh4YGD61Tc3TJjaEY17hDldH' }})

mike Over a year ago

awesome, it worked, i had no idea i could refer to the value of the document i just found with {'$exists':1}, mongodb is pretty cool. where is this use case explained, i could not find this in here: docs.mongodb.org/manual/reference/operator/query/exists you certainly understand mongodb

JohnnyHK Over a year ago

@mike You're not referring to the value of the doc you just found with $exists, you're simply using it to identify the elements to $pull from files, in the same way you used it to identify the documents to update.

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