$elemMatch against two Array elements if one fails - mongodb

Question

A bit odd but this is what I am looking for.
I have an array as follow:
Document 1:
Items: [
{
"ZipCode": "11111",
"ZipCode4" "1234"
}
Document 2:
Items: [
{
"ZipCode": "11111",
"ZipCode4" "0000"
}
I would like to use a single query, and send a filter on ZipCode = 1111 && ZipCode4 = 4321, if this fails, the query should look for ZipCode = 1111 && ZipCode4: 0000
Is there a way to do this in a single query ? or do I need to make 2 calls to my database ?

Answer 1

For matching both data set (11111/4321) and (11111/0000), you can use $or and $and with $elemMatch like the following :
db.test.find({
$or: [{
$and: [{
"Items": {
$elemMatch: { "ZipCode": "11111" }
}
}, {
"Items": {
$elemMatch: { "ZipCode4": "4321" }
}
}]
}, {
$and: [{
"Items": {
$elemMatch: { "ZipCode": "11111" }
}
}, {
"Items": {
$elemMatch: { "ZipCode4": "0000" }
}
}]
}]
})
As you want conditional staging, this is not possible but we can get closer to it like this :
db.test.aggregate([{
$match: {
$or: [{
$and: [{ "Items.ZipCode": "11111" }, { "Items.ZipCode4": "4321" }]
}, {
$and: [{ "Items.ZipCode": "11111" }, { "Items.ZipCode4": "0000" }]
}]
}
}, {
$project: {
Items: 1,
match: {
"$map": {
"input": "$Items",
"as": "val",
"in": {
"$cond": [
{ $and: [{ "$eq": ["$$val.ZipCode", "11111"] }, { "$eq": ["$$val.ZipCode4", "4321"] }] },
true,
false
]
}
}
}
}
}, {
$unwind: "$match"
}, {
$group: {
_id: "$match",
data: {
$push: {
_id: "$_id",
Items: "$Items"
}
}
}
}])
The first $match is for selecting only the items we need
The $project will build a new field that check if this items is from the 1st set of data (11111/4321) or the 2nd set of data (11111/0000).
The $unwind is used to remove the array generated by $map.
The $group group by set of data
So in the end you will have an output like the following :
{ "_id" : true, "data" : [ { "_id" : ObjectId("58af69ac594b51730a394972"), "Items" : [ { "ZipCode" : "11111", "ZipCode4" : "4321" } ] }, { "_id" : ObjectId("58af69ac594b51730a394974"), "Items" : [ { "ZipCode" : "11111", "ZipCode4" : "4321" } ] } ] }
{ "_id" : false, "data" : [ { "_id" : ObjectId("58af69ac594b51730a394971"), "Items" : [ { "ZipCode" : "11111", "ZipCode4" : "0000" } ] } ] }
Your application logic can check if there is _id:true in this output array, just take the corresponding data field for _id:true. If there is _id:false in this object take the corresponding data field for _id:false.
In the last $group, you can also use $addToSet to builds 2 field data1 & data2 for both type of data set but this will be painful to use as it will add null object to the array for each one of the opposite type :
"$addToSet": {
"$cond": [
{ "$eq": ["$_id", true] },
"$data",
null
]
}
Here is a gist