Query ElemMatch an array within an array

Question

I'm trying to query a collection and filter based on values nested within an array and a second array using elemMatch.

{
"email": "[email protected]",
"project" [ {
                projectId: ObjectId("123"),
                preference: [
                            {"name": "name1", "value": true},
                            {"name": "name2", "value": false}
                ]
            }, 
            {
                projectId: ObjectId("456"),
                preference: [
                            {"name": "name1", "value": true},
                            {"name": "name2", "value": true}
                ]
            }
]
}, 
{
"email": "[email protected]",
"project" [ {
                projectId: ObjectId("123"),
                preference: [
                            {"name": "name1", "value": false},
                            {"name": "name2", "value": true}
                ]
            }, 
            {
                projectId: ObjectId("456"),
                preference: [
                            {"name": "name1", "value": true},
                            {"name": "name2", "value": true}
                ]
            }
]
}

I've tried a few different variations of merging the below two queries into one to try and achieve my goal of returning.

{email: "[email protected]"}

db.user.find({"project":{"$elemMatch":{"projectId":ObjectId("123")}}}, {email: 1})
db.user.find({"project.preference":{"$elemMatch":{"$and":[{"name":"name1"}, {"value": true}]}}}, {email: 1})

mickl · Accepted Answer · 2019-01-08 06:33:40Z

1

You can use $unwind to simplify querying multiple levels of nested arrays, try:

db.user.aggregate([
    {  $unwind: "$project" },
    {  $match: { "project.projectId": "123" } },
    {  $unwind: "$project.preference" },
    {  $match: { "project.preference.name": "name1", "project.preference.value": true } },
    {  $project: { _id: 0, email: 1 } }
])

answered Jan 8, 2019 at 6:33

mickl

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