How to use $in operator with pair of attributes - mongodb

Question

Consider this collection
/* 1 */
{
"key" : 1,
"b" : 2,
"c" : 3
}
/* 2 */
{
"key" : 2,
"b" : 5,
"c" : 4
}
/* 3 */
{
"key" : 3,
"b" : 7,
"c" : 9
}
/* 4 */
{
"key" : 4,
"b" : 7,
"c" : 4
}
/* 5 */
{
"key" : 5,
"b" : 2,
"c" : 9
}
I want to use the $in operator and write a query to return the document such (b, c) IN ((2, 3), (7, 9)). It means "return all rows where b is 2 and c is 3 at the same time, OR b is 7 and с is 9 at the same time."
How can I use $in operator to use multiple attribute values.
If I use the following query
db.getCollection('test').find({
$and:[
{b:{$in:[2,7]}},
{c:{$in:[3,9]}}
]
})
then I get following results
(2,3)
(7,9)
(2,9) --> This is unwanted record.
IN SQL world it is possible
SELECT *
FROM demo
WHERE (b, c) IN ((2, 3), (7, 9))
What is the equivalent in Mongo DB?

Answer 1

If I get it right, the thing you are doing is getting all the pairs (2,3),(2,9),(7,3),(7,9).
But you want to match those one by one, so your valid pairs should be (2, 3), (7, 9). To satisfy this, you can match b and c one by one, pair them and "or" them after.
db.getCollection('test').find({
$or: [
{$and: [ {b : 2}, {c : 3} ]},
{$and: [ {b : 7}, {c : 9} ]}
]
})