I have a collection with data like this:
{
"Name": "Steven",
"Children": [
{
"Name": "Liv",
"Children": [
{
"Name": "Milo"
}
]
},
{
"Name": "Mia"
},
{
"Name": "Chelsea"
}
]
},
{
"Name": "Ozzy",
"Children": [
{
"Name": "Jack",
"Children": [
{
"Name": "Pearl"
}
]
},
{
"Name": "Kelly"
}
]
}
Two questions
Can MongoDB flatten the arrays to a structure like this [Steven, Liv, Milo, Mia,Chelsea, Ozzy, Jack, Pearl,Kelly]
How can I find the a document where name is jack, no matter where in the structure it is placed
In general, MongoDB does not perform recursive or arbitrary-depth operations on nested fields. To accomplish objectives 1 and 2 I would reconsider the structure of the data as an arbitrarily nested document is not a good way to model a tree in MongoDB. The MongoDB docs have a good section of modelin tree structures that present several options with examples. Pick the one that best suits your entire use case - they will all make 1 and 2 very easy.
Related
I have a collection with documents like:
{
"_id": "Mongo ObjectID",
"some_prop": "some_value",
"features": [
{ "name": "A", "icon": "01.png" },
{ "name": "B", "icon": "02.png" }
]
}
Another document sample:
{
"_id": "Mongo ObjectID",
"some_prop": "other one",
"features": [
{ "name": "B", "icon": "02.png" },
{ "name": "C", "icon": "03.png" },
{ "name": "D", "icon": "04.png" }
]
}
Notice that in the first document and the second there is the same feature B. This occurs all over many documents.
What I need is to update all features B to a new icon, something like this:
{ "name": "B", "icon": "10.png" }
I need to apply this change for all documents that has a feature with name B.
I already did a very horrible code to get all documents and update one by one in a loop. But my guess is there is a better way to do it, maybe in a single collection.update command? I'm new in MongoDB and so far googling didnt work.
You need to use $positional operator to update the fields inside an array
db.collection.updateMany(
{ "features.name": "B" },
{ "$set": { "features.$.icon": "10.png" }}
)
Let's imagine a mongo collection of - let's say magazines. For some reason, we've ended up storing each issue of the magazine as a separate document. Each article is a subdocument inside an Articles-array, and the authors of each article is represented as a subdocument inside the Writers-array on the Article-subdocument. Only the name and email of the author is stored inside the article, but there is an Writers-array on the magazine level containing more information about each author.
{
"Title": "The Magazine",
"Articles": [
{
"Title": "Mongo Queries 101",
"Summary": ".....",
"Writers": [
{
"Name": "tom",
"Email": "tom#example.com"
},
{
"Name": "anna",
"Email": "anna#example.com"
}
]
},
{
"Title": "Why not SQL instead?",
"Summary": ".....",
"Writers": [
{
"Name": "mike",
"Email": "mike#example.com"
},
{
"Name": "anna",
"Email": "anna#example.com"
}
]
}
],
"Writers": [
{
"Name": "tom",
"Email": "tom#example.com",
"Web": "tom.example.com"
},
{
"Name": "mike",
"Email": "mike#example.com",
"Web": "mike.example.com"
},
{
"Name": "anna",
"Email": "anna#example.com",
"Web": "anna.example.com"
}
]
}
How can one author be completely removed from a magazines?
Finding magazines where the unwanted author exist is quite easy. The problem is pulling the author out of all the sub documents.
MongoDB 3.6 introduces some new placeholder operators, $[] and $[<identity>], and I suspect these could be used with either $pull or $pullAll, but so far, I haven't had any success.
Is it possible to do this in one go? Or at least no more than two? One query for removing the author from all the articles, and one for removing the biography from the magazine?
You can try below query.
db.col.update(
{},
{"$pull":{
"Articles.$[].Writers":{"Name": "tom","Email": "tom#example.com"},
"Writers":{"Name": "tom","Email": "tom#example.com"}
}},
{"multi":true}
);
I have the following structure in MongoDB and I try to remove the documents that contains specific tags. I can't seem to be able to get the $pull work.
In this example, I would like to pull the nested doc that has has tags :["BB"]
Any help will be appreciated !
{
"_id": 123,
"socialItems": {
"facebook": [{
"name": "firstFacebook",
"id": 2
}, {
"name": "secondFB",
"id": 43
}],
"instagram": [{
"name": "firstNstagram",
"id": 4
}],
"pc": [{
"name": "firstPC",
"id": 55,
"tags": [
"ab"
]
}, {
"name": "secondPC",
"id": 66,
"tags": [
"BB"
]
}]
}
}
I assume you are trying to drop the nested 'pc' doc, from the array? You also don't mention if you're using a specific driver for this, so I've assumed you're running this in the Mongo shell.
The following will remove documents from the 'pc' property, when containing the 'BB' tag.
db.collectionName.update({'socialItems.pc.tags': 'BB'}, {$pull: {'socialItems.pc': {tags: 'BB'}}})
Using MongoDB for storage, if I wanted to represent a tree structure of nodes, where child nodes under a single parent always have unique node-names, I believe the standard approach would be to use collections and to manage the node name uniqueness on the app level:
Approach 1: Collection Based Approach for Tree Data
{ "node_name": "home", "title": "Home", "children": [
{ "node_name": "products", "title": "Products", "children": [
{ "node_name": "electronics", "title": "Electronics", "children": [ ] },
{ "node_name": "toys", "title": "Toys", "children": [ ] } ] },
{ "node_name": "services", "title": "Services", "children": [
{ "node_name": "repair", "title": "Repair", "children": [ ] },
{ "node_name": "training", "title": "Training"", "children": [ ] } ] } ] }
I have however thought of the following alternate approach, where node-names become "Object Map" field names, and we do without collections altogether:
Approach 2: Object-Map Based Approach (without Collections)
// NOTE: We don't have the equivalent of "none_name":"home" at the root, but that's not an issue in this case
{ "title": "Home", "children": {
"products": { "title": "Products", children": {
"electronics": { "title": "Electronics", "children": { } },
"toys": { "title": "Toys", "children": { } } } },
"services": { "title": "Services", children": {
"repair": { "title": "Repair", "children": { } },
"training": { "title": "Training", "children": { } } } } } }
The question is:
Strictly from a MongoDB perspective (considering querying, performance, data maintainability and data-size and server scaling), are there any major issues with Approach #2 (over #1)?
EDIT: After getting to know MongoDB a bit better (and thanks to Neil's comments below), I realized that both options of this question are generally the wrong way to go, because they assume that it makes sense to store multiple nodes in a single MongoDB document. Ultimately, each "node" should be a separate document and (as Neil Lunn stated in the comments) there are various ways to implement a hierarchy tree, as seen here: Model Tree Structures in MongoDB
I think this use-case is not good for Mongo DB, because:
there's(MongoDB 2.6) no compress algorithm (your documents will be too large)
Mongo DB use database-level locks (when you want one large document, all DB operations will be blocked)
it will be hard to index
I think better solution will be some relational DB for this use-case.
Given the following MongoDB example collection ("schools"), how do you remove student "111" from all clubs?
[
{
"name": "P.S. 321",
"structure": {
"principal": "Fibber McGee",
"vicePrincipal": "Molly McGee",
"clubs": [
{
"name": "Chess",
"students": [
ObjectId("111"),
ObjectId("222"),
ObjectId("333")
]
},
{
"name": "Cricket",
"students": [
ObjectId("111"),
ObjectId("444")
]
}
]
}
},
...
]
I'm hoping there's some way other than using cursors to loop over every school, then every club, then every student ID in the club...
MongoDB doesn't have a great support for arrays within arrays (within arrays ...). The simplest solution I see is to read the whole document into your app, modify it there and then save. This way, of course, the operation is not atomic, but for your app it might be ok.