How to remove an element from a doubly-nested array in a MongoDB document

I have a document structure something along the lines of the following:

{
"_id" : "777",
"someKey" : "someValue",
"someArray" : [
    {
        "name" : "name1",
        "someNestedArray" : [
            {
                "name" : "value&开发者_如何学运维quot;
            },
            {
                "name" : "delete me"
            }
        ]
    }
  ]
}

I want to delete the nested array element with the value "delete me".

I know I can find documents which match this description using nested $elemMatch expressions. What is the query syntax for removing the element in question?

---

To delete the item in question you're actually going to use an update. More specifically you're going to do an update with the $pull command which will remove the item from the array.

db.temp.update(
  { _id : "777" },
  {$pull : {"someArray.0.someNestedArray" : {"name":"delete me"}}}
)

There's a little bit of "magic" happening here. Using .0 indicates that we know that we are modifying the 0th item of someArray. Using {"name":"delete me"} indicates that we know the exact data that we plan to remove.

This process works just fine if you load the data into a client and then perform the update. This process works less well if you want to do "generic" queries that perform these operations.

I think it's easiest to simply recognize that updating arrays of sub-documents generally requires that you have the original in memory at some point.

---

In response to the first comment below, you can probably help your situation by changing the data structure a little

"someObjects" : {
  "name1":  {
        "someNestedArray" : [
            {
                "name" : "value"
            },
            {
                "name" : "delete me"
            }
        ]
    }
}

Now you can do {$pull : { "someObjects.name1.someNestedArray" : ...

Here's the problem with your structure. MongoDB does not have very good support for manipulating "sub-arrays". Your structure has an array of objects and those objects contain arrays of more objects.

If you have the following structure, you are going to have a difficult time using things like $pull:

array [
  { subarray : array [] },
  { subarray : array [] },
]

If your structure looks like that and you want to update subarray you have two options:

1. Change your structure so that you can leverage $pull.
2. Don't use $pull. Load the entire object into a client and use findAndModify.

---

MongoDB 3.6 added $[] operator that facilitates updates to arrays that contain embedded documents. So the problem can be solved by:

db.test.update(
  { _id : "777" },
  {$pull : {"someArray.$[].someNestedArray" : {"name":"delete me"}}}
)

---

As @Melkor has commented (should probably be an answer as itself),

If you do not know the index use:

{
    _id: TheMainID, 
    "theArray._id": TheArrayID
},
{
    $pull: {
        "theArray.$.theNestedArray": {
            _id: theNestedArrayID
        }
    }
}

---

From MongoDB 3.6 on you can use arrayFilters to do this:

db.test.update(
  { _id: "777" }, 
  { $pull: { "someArray.$[elem].someNestedArray": { name: "delete me" } } },
  { arrayFilters: [{ "elem.name": "name1"}] }
)

see also https://docs.mongodb.com/manual/reference/operator/update/positional-filtered/index.html#update-all-documents-that-match-arrayfilters-in-an-array

---

Other example and usage could be like this:

{

    "company": {
        "location": {
            "postalCode": "12345",
            "Address": "Address1",
            "city": "Frankfurt",
            "state": "Hessen",
            "country": "Germany"
        },
        "establishmentDate": "2019-04-29T14:12:37.206Z",
        "companyId": "1",
        "ceo": "XYZ"
    },
    "items": [{
            "name": "itemA",
            "unit": "kg",
            "price": "10"
        },
        {
            "name": "itemB",
            "unit": "ltr",
            "price": "20"
        }

    ]
}

1. DELETE : Mongodb Query to delete ItemB:

db.getCollection('test').update(   
    {"company.companyId":"1","company.location.city":"Frankfurt"},
    {$pull : {"items" : {"name":"itemB"}}}
)

2. FIND: Find query for itemB:

db.getCollection('test').find(
    {"company.companyId":"1","company.location.city":"Frankfurt","items.name":"itemB"},
    { "items.$": 1 }
)

3.UPDATE : update query for itemB:

db.getCollection('test').update
(
 {"company.companyId":"1","company.location.city":"Frankfurt","items.name":"itemB"},
 { $set: { "items.$[].price" : 90 }}, 
   { multi: true });