Find documents matching multiple fields in an object array in MongoDB - arrays

Question

Let's say I have an array of objects (let us call that array A) and I need a query to find a collection in MongoDB for all documents matching one of it's fields to one of the properties of object 1 in array A and another field to some other property in the same object in array A.
The documents do not have all the properties that the objects in array A have.
To make things clear...
Array A would look something like this...
[{
id_bus:1,
id_bus_variation:13,
....
},{
id_bus:2,
id_bus_variation:184,
....
},{
id_bus:3,
id_bus_variation:13,
....
}]
The documents in my database include those two properties and I need to match those two at the same time. For example, I need to find in my database the docs that have id_bus == 1 and id_bus_variation == 13, and also the ones that have id_bus == 2 and id_bus_variation == 184 but not the ones that id_bus == 4 and id_bus_variation == 13.
I really don't have any idea of how to do this using a single query, the only way around it I found is to go through array A and execute a query for each of it's elements, matching all the fields I need, but that doesn't seem efficient.

Answer 1

It sounds like you want to match the structure of a subdocument in an array to one of many possible structures specified by an array. I'll give an example of how to do this in the mongo shell:
> db.test.insert({
"_id" : 0,
bus : [
{ "id_bus" : 1, "id_bus_variation" : 1 },
{ "id_bus" : 2, "id_bus_variation" : 2 },
{ "id_bus" : 3, "id_bus_variation" : 3 }
]
})
> db.test.insert({
"_id" : 1,
bus : [
{ "id_bus" : 1, "id_bus_variation" : 3 },
{ "id_bus" : 2, "id_bus_variation" : 2 },
{ "id_bus" : 3, "id_bus_variation" : 1 }
]
})
> db.test.insert({
"_id" : 2,
bus : [
{ "id_bus" : 1, "id_bus_variation" : 1 },
{ "id_bus" : 2, "id_bus_variation" : 3 },
{ "id_bus" : 3, "id_bus_variation" : 2 }
]
})
If we want to return all documents where (id_bus = 2 and id_bus_variation = 3) or (id_bus = 3 and id_bus_variation = 3), as specified in an array
> var match = [{ "id_bus" : 2, "id_bus_variation" : 3 }, { "id_bus" : 3, "id_bus_variation" : 3 }];
We can construct the query programmatically:
> var query = { "$or" : [] }
> for (var i = 0; i < match.length; i++) {
query["$or"].push({ "bus" : { "$elemMatch" : match[i] } });
}
> db.test.find(query, { "_id" : 1 }) // just get _id's for easy reading
{ "_id" : 0 }
{ "_id" : 2 }
We get the expected results.

Answer 2

I don't know if I understand your Question.
Your collection could be like
{
"_id" : ObjectId("53de54c1560b7815e123792f"),
"bus" : [
{
"id_bus" : 1,
"id_bus_variation" : 13
},
{
"id_bus" : 2,
"id_bus_variation" : 184
},
{
"id_bus" : 3,
"id_bus_variation" : 13
}
]
}
And you want retrieve the document only if id_bus and id_bus_variation are "true"
You can try it
db.stack.find({$and:[{ "bus.id_bus" : 1,"bus.id_bus_variation" : 13},{"bus.id_bus" : 2,"bus.id_bus_variation" : 184}]})
and retrieve the Document only if bus.id_bus and bus.id_bus_variation are in Document.
For Example
db.stack.find({$and:[{ "bus.id_bus" : 1,"bus.id_bus_variation" : 13},{"bus.id_bus" : 2,"bus.id_bus_variation" : 184},{"bus.id_bus":4}]})
you haven't any result.
If you want exactly the element inside Object
db.stack.find ( { bus: { "$elemMatch" : { id_bus:1, id_bus_variation : 13} } } )
The document return only if both value are "true"