问题
I have a document in MongoDB that looks like this:
{ users: ["2", "3", "4"] }
I'm try to query this document by matching the users array.
db.things.find( { users: { $all: [ "2", "3", "4" ] } } )
That query works, but would also return this document:
{ users: ["2", "3", "4", "5"] }
Last requirement is to be able to query the users array with the elements out of order, say [ "3", "4", "2" ] in the query, and it be able to return my first document listed.
Any help would be greatly appreciated. Thanks in advance.
I'm also using mongoid, if that has a helper that anyone knows about, but can do a straight mongo query if I need to.
回答1:
You could combine your query with a { users : { $size : 3 } } clause and adjust the size to match the number of users you are querying for. That would ensure that you are getting the exact set, and not a subset.
If the elements are out of order, you might need to do a { users : { $exists : "1" } } for each, and combine those and the $size clause all together.
回答2:
This answer is incorrect.
to query a document for exactly matches in an array do this.
db.things.insert({a:[1,2]});
db.things.insert({a:[1,2,3]});
db.things.find({a:[1,2]});
returns {a:[1,2]}
Hope this helps - it's so obvious that it's not in the docs
来源：https://stackoverflow.com/questions/6165121/mongodb-query-an-array-for-an-exact-element-match-but-may-be-out-of-order