Complex mongodb document search - mongodb

Question

I'm attempting to write a find query where one of the keys is unknown at the time the query is run, for example on the following document I'm interested in returning the document if "setup" is true:
{
"a": {
"randomstringhere": {
"setup": true
}
}
}
However I can't work how to wildcard the "randomstringhere" field as it changes for each document in the collection.
Can somebody help?

Answer 1

There is not much you can do with that. But you can modify your collection schema like
{
"a": [
{
"keyName": "randomstringhere",
"setup": true
},
//...
]
}
you can than write query to look
{
'a' : { $elemMatch: { setup: true } ,
}

Answer 2

You can't do this with a single query, as with the current design you would need a mechanism to get all the random keys that you need and then assemble the query document that uses the $or operator in the event that you get a list of variable key name.
The first part of your operation is possible using Map-Reduce. The following mapreduce operation will populate a separate collection called collectionKeys with all the random keys as the _id values:
mr = db.runCommand({
"mapreduce": "collection",
"map" : function() {
for (var key in this.a) { emit(key, null); }
},
"reduce" : function() { },
"out": "collectionKeys"
})
To get a list of all the random keys, run distinct on the resulting collection:
db[mr.result].distinct("_id")
Example Ouput
["randomstring_1", "randomstring_2", "randomstring_3", "randomstring_4", ...]
Now given the list above, you can assemble your query by creating an object that will have its properties set within a loop. Normally your query document will have this structure:
var query = {
"$or": [
{ "a.randomstring_1.setup": true },
{ "a.randomstring_2.setup": true },
{ "a.randomstring_3.setup": true }
]
};
which you can then use in your query:
db.collection.find(query)
So using the above list of subdocument keys, you can dynamically construct the above using JavaScript's map() method:
mr = db.runCommand({
"mapreduce": "collection", // your collection name
"map" : function() { // map function
for (var key in this.a) { emit(key, null); }
},
"reduce" : function() { }, // empty reducer that doesn't do anything
"out": "collectionKeys" // output collection with results
})
var randomstringKeysList = db[mr.result].distinct("_id"),
orOperator = randomstringKeysList.map(function (key){
var o = {};
o["a."+ key +".setup"] = true;
return o;
}),
query = { "$or": orOperator };
db.collection.find(query);