combining regex and embedded objects in mongodb queries - regex

Question

I am trying to combine regex and embedded object queries and failing miserably. I am either hitting a limitation of mongodb or just getting something slightly wrong maybe someone out ther has encountered this. The documentation certainly does'nt cover this case.
data being queried:
{
"_id" : ObjectId("4f94fe633004c1ef4d892314"),
"productname" : "lightbulb",
"availability" : [
{
"country" : "USA",
"storeCode" : "abc-1234"
},
{
"country" : "USA",
"storeCode" : "xzy-6784"
},
{
"country" : "USA",
"storeCode" : "abc-3454"
},
{
"country" : "CANADA",
"storeCode" : "abc-6845"
}
]
}
assume the collection contains only one record
This query returns 1:
db.testCol.find({"availability":{"country" : "USA","storeCode":"xzy-6784"}}).count();
This query returns 1:
db.testCol.find({"availability.storeCode":/.*/}).count();
But, this query returns 0:
db.testCol.find({"availability":{"country" : "USA","storeCode":/.*/}}).count();
Does anyone understand why? Is this a bug?
thanks

Answer 1

You are referencing the embedded storecode incorrectly - you are referencing it as an embedded object when in fact what you have is an array of objects. Compare these results:
db.testCol.find({"availability.0.storeCode":/x/});
db.testCol.find({"availability.0.storeCode":/a/});
Using your sample doc above, the first one will not return, because the first storeCode does not have an x in it ("abc-1234"), the second will return the document. That's fine for the case where you are looking at a single element of the array and pass in the position. In order to search all of the objcts in the array, you want $elemMatch
As an example, I added this second example doc:
{
"_id" : ObjectId("4f94fe633004c1ef4d892315"),
"productname" : "hammer",
"availability" : [
{
"country" : "USA",
"storeCode" : "abc-1234"
},
]
}
Now, have a look at the results of these queries:
PRIMARY> db.testCol.find({"availability" : {$elemMatch : {"storeCode":/a/}}}).count();
2
PRIMARY> db.testCol.find({"availability" : {$elemMatch : {"storeCode":/x/}}}).count();
1