Suppose, I have the following database:
{
_id: 1,
name: 'Alice',
courses: [
{
_id: 'DB103',
credits: 6
},
{
_id: 'ML203',
credits: 4
}
]
},
{
_id: 2,
name: 'Bob',
courses: []
}
I now want to 'upsert' the document with the course id 'DB103' in both documents. Although the _id field should remain the same, the credits field value should change (i.e. to 4). In the first document, the respective field should be changed, in the second one, {_id: 'DB103', credits: 4} should be inserted into the courses array.
Is there any possibility in MongoDB to handle both cases?
Sure, I could search with $elemMatch in courses for 'DB103' and if I haven't found it, insert, otherwise update the value. But these are two steps and I would like to do both in just one.
Related
Learning MongoDB so I hope that this is not a duplicate question.
So big picture. Users can add/remove items from their cart (which is an array).
The cart array holds objects who are structured as follows: {_id: 123r32, qty: 2}
The user document is structured as follows:
_id: 123432423,
username: johndoe,
email: johndoe#mail.com,
cart: [
{
_id: wefw3423,
qty: 100
}
]
So adding to the array is fine:
db.users.updateOne({_id: req.user.id}, {$push: {cart: {_id: req.body.id, qty: req.body.qty}}})
But when I push, I don't want to add a duplicate. I want to just adjust the qty (add/subtract) accordingly. If no instance of that _id exists, push.
Thank you for reading and your help! Should you need additional information, please ask I shall provide!.
EDIT:
Additional information. The request body (req.body) will contain only ONE item. So updateMany will not be required here.
db.users.updateOne({_id: req.user.id}, {$set: { "cart.$[element]": {_id:"wefw3423",qty:50}}, { arrayFilters: [ { element: _id:"wefw3423" } ]},{ upsert:true})
MongoDB reference :
https://docs.mongodb.com/manual/reference/operator/update/positional-filtered/#mongodb-update-up.---identifier--
I have a collection full of products each of which has a subdocument array of up to 100 variants (SKUs) of that product:
e.g.
{
'_id': 12345678,
'handle': 'my-product-handle',
'updated': false
'variants': [
{
'_id': 123412341234,
'sku': 'abc123',
'inventory': 1
},
{
'_id': 123412341235,
'sku': 'abc124',
'inventory': 2
},
...
]
}
My goal is to be able to update the inventory quantity of all instances of a SKU number. It is important to note that in the system I'm working with, SKUs are not unique. Therefore, if a SKU shows up multiple times in a single product or across multiple products, they all need to be updated to the new inventory quantity.
Furthermore, I need the "updated" field to be changed to "true" *only if the inventory quantity for that SKU has changed"
As an example, if I want to update all instances of SKU "abc123" to have 25 inventory, the example of above would return this:
{
'_id': 12345678,
'handle': 'my-product-handle',
'updated': true
'variants': [
{
'_id': 123412341234,
'sku': 'abc123',
'inventory': 25
},
{
'_id': 123412341235,
'sku': 'abc124',
'inventory': 2
},
...
]
}
Thoughts?
MongoDB 3.6 has introduced the filtered positional operator $[<identifier>] which can be used to update multiple elements of an array which match an array filter condition. You can read more about this operator here: https://docs.mongodb.com/manual/reference/operator/update/positional-filtered/
For example, to update all elements of the variants array where sku is "abc123" across every document in the collection:
db.collection.update({}, { $set: { "variants.$[el].inventory": 25 }}, { multi: true, arrayFilters: [{ "el.sku": "abc123"}] })
Unfortunately I'm not aware of any way in a single query to update a document's field based on whether another field in the document was updated. This is something you would have to implement with some client-side logic and a second query.
EDIT (thanks to Asya's comment):
You can do this in a single query by only matching documents which will be modified. So if nMatched and nModified are necessarily equal, you can just set updated to true. For example, I think this would solve the problem in a single query:
db.collection.update({ variants: { $elemMatch: { inventory: { $ne: 25 }, sku: "abc123" } } }, { $set: { "variants.$[el].inventory": 25, updated: true }}, { multi: true, arrayFilters: [{ "el.sku": "abc123"}] })
First you match documents where the variants array contains documents where the sku is "abc123" and the inventory does not equal the number you are setting it to. Then you go ahead and set the inventory on all matching subdocuments and set updated to true.
I have the following schema:
var lessonSchema = mongoose.Schema({
_id: mongoose.Schema.Types.ObjectId,
name: String,
students: [{
_id: mongoose.Schema.Types.ObjectId,
attendance: {
type: Boolean,
default: false,
},
}],
});
The students array is an array of students who attended the particular lesson. I want to find a lesson using whether a particular user is present in the students array and then sent only that element of the students array which corresponds to the user making the request, along with all other fields as it is. For example, the query should return:
{
_id: 'objectid',
name: 'lesson-name'
students: [details of just the one student corresponding to req.user._id]
}
I tried using:
Lesson.find({'students._id': String(req.user._id)}, {"students.$": 1})
The query returns the document with just the id and the relevant element from the students array:
{
_id: 'objectid'
students: [details of the one student corresponding to req.user._id]
}
I tried using:
Lesson.find({'students._id': mongoose.Types.ObjectId(req.user._id)})
This returns the document with the details of all the students:
{
_id: 'objectid',
name: 'lesson-name'
students: [array containing details of all the students who attended the lesson]
}
How can I modify the query to return it the way I want?
You can return the name field by adding it to the projection object like this:
Lesson.find({ "students._id": String(req.user._id) }, { "name": 1, "students.$": 1 })
When you add a projection object (2nd parameter to find), the _id field is returned by default, plus whichever fields you set to 1.
Therefore, you were returning just the _id and the desired student but not the name field.
If you want to return all other fields and just limit the array to the matched item then you can make use of $slice in your projection:
Lesson.find({ "students._id": String(req.user._id) }, { "students.$": { $slice: 1 } })
I have the following schema:
{
_id: objectID('593f8c591aa95154cfebe612'),
name: 'test'
businesses: [
{
_id: objectID('5967bd5f1aa9515fd9cdc87f'),
likes: [objectID('595796811aa9514c862033a1'), objectID('593f8c591ba95154cfebe790')]
}
{
_id: objectID('59579ff91aa9514f600cbba6'),
likes: [objectID('693f8c554aa95154cfebe146'), objectID('193f8c591ba95154cfeber790')]
}
]
}
I need to update "businesses.likes" where businesses._id equal to a center value and where businesses.likes contains certain objectID.
If the objectID exists in the array, I want to remove it.
This is what I have tried and didn't work correctly, because $in is searching in all the subdocuments, instead of the only subdocument where businesses._id = with my value:
db.col.update(
{ businesses._id: objectID('5967bd5f1aa9515fd9cdc87f'), 'businesses.likes': {$in: [objectID('193f8c591ba95154cfeber790')]}},
{$pull: {'businesses.$.likes': objectID('193f8c591ba95154cfeber790')}}
)
Any ideas how how I can write the query? Keep in mind that businesses.likes from different businesses can have the same objectID's.
I have a collection in which unique documents from a different collection can appear over and over again (in example below item), depending on how much a user shares them. I want to create an aggregate query which finds the most shared documents. There is no $match necessary because I'm not matching a certain criteria, I'm just querying the most shared. Right now I have:
db.stories.aggregate(
{
$group: {
_id:'item.id',
'item': {
$first: '$item'
},
'total': {
$sum: 1
}
}
}
);
However this only returns 1 result. It occurs to me I might just need to do a simple find query, but I want the results aggregated, so that each result has the item and total is how many times it's appeared in the collection.
Example of a document in the stories collection:
{
_id: ObjectId('...'),
user: {
id: ObjectId('...'),
propertyA: ...,
propertyB: ...,
etc
},
item: {
id: ObjectId('...'),
propertyA: ...,
propertyB: ...,
etc
}
}
users and items each have their own collections as well.
Change the line
_id:'item.id'
to
_id:'$item.id'
Currently you group by the constant 'item.id' and therefore you only get one document as result.