Related
So I have a collection called Cars that have some fields that are the same, but I want to be able to only get one of the documents based on that field.
[
{
_id:'12345',
model:'Honda'
},
{
_id:'12346',
model:'Honda'
},
{
_id:'12347',
model:'Honda'
},
{
_id:'12348',
model:'Toyota'
},
{
_id:'12349',
model:'Volkswagen'
},
{
_id:'12349',
model:'Volkswagen'
},
]
So here, I want to be able to get the distinct document based on the model field. I just want one document per model field.
first, you want to update mongoose v3 or up
the solution is to use the distinct function
Cars.find().distinct('model', function(error, models) {});
I hope it will help you :)
Use $first to pick a document in $group stage. Then do some wrangling with $unwind and $replaceRoot to retrieve the document.
db.collection.aggregate([
{
$group: {
_id: "$model",
doc: {
$first: "$$ROOT"
}
}
},
{
"$unwind": "$doc"
},
{
"$replaceRoot": {
"newRoot": "$doc"
}
}
])
Here is the Mongo Playground for your reference.
I am working on an app that uses MongoDB (I use Mongoose) as its database.
I have a question, suppose I have this kind of schema:
[{
"user_id":"2328292073"
"username":"Bob",
"subscriptions":[
{
"id":"38271281,
"payments":[
{
"id":"00001",
"amount":"1900"
},
{
"id":"00002",
"amount":"2000"
},
{
"id":"00003",
"amount":"3000"
}
]
}
]
}]
In my case I want to get the payments array for subscription with id = '38271281' of user with id '2328292073', but I just want to retrieve the payment array, nothing else
My query is the following:
Mongoose.findOne({
"user_id": "2328292073",
"subscriptions.id": "38271281"
},
{
"subscriptions.payments": 1
})
But I get the entire document of subscriptions. How can i get the payment array only?
you can try using unwind if you want filteration from db only.
Mongoose.aggregate([
{
'$match': {
'user_id': '2328292093'
}
}, {
'$unwind': {
'path': '$subscriptions'
}
}, {
'$match': {
'subscriptions.id': '38271281'
}
}
])
if you will have multiple documents having same subscription id then you have to group it .
using code level filter function can also be one another approach to do this .
You can try aggregation operators in projection in find method or also use aggregation method,
$reduce to iterate loop of subscriptions and check the condition if id matched then return payment array
db.collection.find({
"user_id": "2328292073",
"subscriptions.id": "38271281"
},
{
payments: {
$reduce: {
input: "$subscriptions",
initialValue: [],
in: {
$cond: [
{ $eq: ["$$this.id", "38271281"] },
"$$this.payments",
"$$value"
]
}
}
}
})
Playground
In MongoDB, is it possible to update the value of a field using the value from another field? The equivalent SQL would be something like:
UPDATE Person SET Name = FirstName + ' ' + LastName
And the MongoDB pseudo-code would be:
db.person.update( {}, { $set : { name : firstName + ' ' + lastName } );
The best way to do this is in version 4.2+ which allows using the aggregation pipeline in the update document and the updateOne, updateMany, or update(deprecated in most if not all languages drivers) collection methods.
MongoDB 4.2+
Version 4.2 also introduced the $set pipeline stage operator, which is an alias for $addFields. I will use $set here as it maps with what we are trying to achieve.
db.collection.<update method>(
{},
[
{"$set": {"name": { "$concat": ["$firstName", " ", "$lastName"]}}}
]
)
Note that square brackets in the second argument to the method specify an aggregation pipeline instead of a plain update document because using a simple document will not work correctly.
MongoDB 3.4+
In 3.4+, you can use $addFields and the $out aggregation pipeline operators.
db.collection.aggregate(
[
{ "$addFields": {
"name": { "$concat": [ "$firstName", " ", "$lastName" ] }
}},
{ "$out": <output collection name> }
]
)
Note that this does not update your collection but instead replaces the existing collection or creates a new one. Also, for update operations that require "typecasting", you will need client-side processing, and depending on the operation, you may need to use the find() method instead of the .aggreate() method.
MongoDB 3.2 and 3.0
The way we do this is by $projecting our documents and using the $concat string aggregation operator to return the concatenated string.
You then iterate the cursor and use the $set update operator to add the new field to your documents using bulk operations for maximum efficiency.
Aggregation query:
var cursor = db.collection.aggregate([
{ "$project": {
"name": { "$concat": [ "$firstName", " ", "$lastName" ] }
}}
])
MongoDB 3.2 or newer
You need to use the bulkWrite method.
var requests = [];
cursor.forEach(document => {
requests.push( {
'updateOne': {
'filter': { '_id': document._id },
'update': { '$set': { 'name': document.name } }
}
});
if (requests.length === 500) {
//Execute per 500 operations and re-init
db.collection.bulkWrite(requests);
requests = [];
}
});
if(requests.length > 0) {
db.collection.bulkWrite(requests);
}
MongoDB 2.6 and 3.0
From this version, you need to use the now deprecated Bulk API and its associated methods.
var bulk = db.collection.initializeUnorderedBulkOp();
var count = 0;
cursor.snapshot().forEach(function(document) {
bulk.find({ '_id': document._id }).updateOne( {
'$set': { 'name': document.name }
});
count++;
if(count%500 === 0) {
// Excecute per 500 operations and re-init
bulk.execute();
bulk = db.collection.initializeUnorderedBulkOp();
}
})
// clean up queues
if(count > 0) {
bulk.execute();
}
MongoDB 2.4
cursor["result"].forEach(function(document) {
db.collection.update(
{ "_id": document._id },
{ "$set": { "name": document.name } }
);
})
You should iterate through. For your specific case:
db.person.find().snapshot().forEach(
function (elem) {
db.person.update(
{
_id: elem._id
},
{
$set: {
name: elem.firstname + ' ' + elem.lastname
}
}
);
}
);
Apparently there is a way to do this efficiently since MongoDB 3.4, see styvane's answer.
Obsolete answer below
You cannot refer to the document itself in an update (yet). You'll need to iterate through the documents and update each document using a function. See this answer for an example, or this one for server-side eval().
For a database with high activity, you may run into issues where your updates affect actively changing records and for this reason I recommend using snapshot()
db.person.find().snapshot().forEach( function (hombre) {
hombre.name = hombre.firstName + ' ' + hombre.lastName;
db.person.save(hombre);
});
http://docs.mongodb.org/manual/reference/method/cursor.snapshot/
Starting Mongo 4.2, db.collection.update() can accept an aggregation pipeline, finally allowing the update/creation of a field based on another field:
// { firstName: "Hello", lastName: "World" }
db.collection.updateMany(
{},
[{ $set: { name: { $concat: [ "$firstName", " ", "$lastName" ] } } }]
)
// { "firstName" : "Hello", "lastName" : "World", "name" : "Hello World" }
The first part {} is the match query, filtering which documents to update (in our case all documents).
The second part [{ $set: { name: { ... } }] is the update aggregation pipeline (note the squared brackets signifying the use of an aggregation pipeline). $set is a new aggregation operator and an alias of $addFields.
Regarding this answer, the snapshot function is deprecated in version 3.6, according to this update. So, on version 3.6 and above, it is possible to perform the operation this way:
db.person.find().forEach(
function (elem) {
db.person.update(
{
_id: elem._id
},
{
$set: {
name: elem.firstname + ' ' + elem.lastname
}
}
);
}
);
I tried the above solution but I found it unsuitable for large amounts of data. I then discovered the stream feature:
MongoClient.connect("...", function(err, db){
var c = db.collection('yourCollection');
var s = c.find({/* your query */}).stream();
s.on('data', function(doc){
c.update({_id: doc._id}, {$set: {name : doc.firstName + ' ' + doc.lastName}}, function(err, result) { /* result == true? */} }
});
s.on('end', function(){
// stream can end before all your updates do if you have a lot
})
})
update() method takes aggregation pipeline as parameter like
db.collection_name.update(
{
// Query
},
[
// Aggregation pipeline
{ "$set": { "id": "$_id" } }
],
{
// Options
"multi": true // false when a single doc has to be updated
}
)
The field can be set or unset with existing values using the aggregation pipeline.
Note: use $ with field name to specify the field which has to be read.
Here's what we came up with for copying one field to another for ~150_000 records. It took about 6 minutes, but is still significantly less resource intensive than it would have been to instantiate and iterate over the same number of ruby objects.
js_query = %({
$or : [
{
'settings.mobile_notifications' : { $exists : false },
'settings.mobile_admin_notifications' : { $exists : false }
}
]
})
js_for_each = %(function(user) {
if (!user.settings.hasOwnProperty('mobile_notifications')) {
user.settings.mobile_notifications = user.settings.email_notifications;
}
if (!user.settings.hasOwnProperty('mobile_admin_notifications')) {
user.settings.mobile_admin_notifications = user.settings.email_admin_notifications;
}
db.users.save(user);
})
js = "db.users.find(#{js_query}).forEach(#{js_for_each});"
Mongoid::Sessions.default.command('$eval' => js)
With MongoDB version 4.2+, updates are more flexible as it allows the use of aggregation pipeline in its update, updateOne and updateMany. You can now transform your documents using the aggregation operators then update without the need to explicity state the $set command (instead we use $replaceRoot: {newRoot: "$$ROOT"})
Here we use the aggregate query to extract the timestamp from MongoDB's ObjectID "_id" field and update the documents (I am not an expert in SQL but I think SQL does not provide any auto generated ObjectID that has timestamp to it, you would have to automatically create that date)
var collection = "person"
agg_query = [
{
"$addFields" : {
"_last_updated" : {
"$toDate" : "$_id"
}
}
},
{
$replaceRoot: {
newRoot: "$$ROOT"
}
}
]
db.getCollection(collection).updateMany({}, agg_query, {upsert: true})
(I would have posted this as a comment, but couldn't)
For anyone who lands here trying to update one field using another in the document with the c# driver...
I could not figure out how to use any of the UpdateXXX methods and their associated overloads since they take an UpdateDefinition as an argument.
// we want to set Prop1 to Prop2
class Foo { public string Prop1 { get; set; } public string Prop2 { get; set;} }
void Test()
{
var update = new UpdateDefinitionBuilder<Foo>();
update.Set(x => x.Prop1, <new value; no way to get a hold of the object that I can find>)
}
As a workaround, I found that you can use the RunCommand method on an IMongoDatabase (https://docs.mongodb.com/manual/reference/command/update/#dbcmd.update).
var command = new BsonDocument
{
{ "update", "CollectionToUpdate" },
{ "updates", new BsonArray
{
new BsonDocument
{
// Any filter; here the check is if Prop1 does not exist
{ "q", new BsonDocument{ ["Prop1"] = new BsonDocument("$exists", false) }},
// set it to the value of Prop2
{ "u", new BsonArray { new BsonDocument { ["$set"] = new BsonDocument("Prop1", "$Prop2") }}},
{ "multi", true }
}
}
}
};
database.RunCommand<BsonDocument>(command);
MongoDB 4.2+ Golang
result, err := collection.UpdateMany(ctx, bson.M{},
mongo.Pipeline{
bson.D{{"$set",
bson.M{"name": bson.M{"$concat": []string{"$lastName", " ", "$firstName"}}}
}},
)
I know that MongoDB supports the syntax find{array.0.field:"value"}, but I specifically want to do this for the last element in the array, which means I don't know the index. Is there some kind of operator for this, or am I out of luck?
EDIT: To clarify, I want find() to only return documents where a field in the last element of an array matches a specific value.
In 3.2 this is possible. First project so that myField contains only the last element, and then match on myField.
db.collection.aggregate([
{ $project: { id: 1, myField: { $slice: [ "$myField", -1 ] } } },
{ $match: { myField: "myValue" } }
]);
You can use $expr ( 3.6 mongo version operator ) to use aggregation functions in regular query.
Compare query operators vs aggregation comparison operators.
For scalar arrays
db.col.find({$expr: {$gt: [{$arrayElemAt: ["$array", -1]}, value]}})
For embedded arrays - Use $arrayElemAt expression with dot notation to project last element.
db.col.find({$expr: {$gt: [{"$arrayElemAt": ["$array.field", -1]}, value]}})
Spring #Query code
#Query("{$expr:{$gt:[{$arrayElemAt:[\"$array\", -1]}, ?0]}}")
ReturnType MethodName(ArgType arg);
Starting Mongo 4.4, the aggregation operator $last can be used to access the last element of an array:
For instance, within a find query:
// { "myArray": ["A", "B", "C"] }
// { "myArray": ["D"] }
db.collection.find({ $expr: { $eq: [{ $last: "$myArray" }, "C"] } })
// { "myArray": ["A", "B", "C"] }
Or within an aggregation query:
db.collection.aggregate([
{ $addFields: { last: { $last: "$myArray" } } },
{ $match: { last: "C" } }
])
use $slice.
db.collection.find( {}, { array_field: { $slice: -1 } } )
Editing:
You can make use of
{ <field>: { $elemMatch: { <query1>, <query2>, ... } } } to find a match.
But it won't give exactly what you are looking for. I don't think that is possible in mongoDB yet.
I posted on the official Mongo Google group here, and got an answer from their staff. It appears that what I'm looking for isn't possible. I'm going to just use a different schema approach.
Version 3.6 use aggregation to achieve the same.
db.getCollection('deviceTrackerHistory').aggregate([
{
$match:{clientId:"12"}
},
{
$project:
{
deviceId:1,
recent: { $arrayElemAt: [ "$history", -1 ] }
}
}
])
You could use $position: 0 whenever you $push, and then always query array.0 to get the most recently added element. Of course then, you wont be able to get the new "last" element.
Not sure about performance, but this works well for me:
db.getCollection('test').find(
{
$where: "this.someArray[this.someArray.length - 1] === 'pattern'"
}
)
You can solve this using aggregation.
model.aggregate([
{
$addFields: {
lastArrayElement: {
$slice: ["$array", -1],
},
},
},
{
$match: {
"lastArrayElement.field": value,
},
},
]);
Quick explanations. aggregate creates a pipeline of actions, executed sequentially, which is why it takes an array as parameter. First we use the $addFields pipeline stage. This is new in version 3.4, and basically means: Keep all the existing fields of the document, but also add the following. In our case we're adding lastArrayElement and defining it as the last element in the array called array. Next we perform a $match pipeline stage. The input to this is the output from the previous stage, which includes our new lastArrayElement field. Here we're saying that we only include documents where its field field has the value value.
Note that the resulting matching documents will include lastArrayElement. If for some reason you really don't want this, you could add a $project pipeline stage after $match to remove it.
For the answer use $arrayElemAt,if i want orderNumber:"12345" and the last element's value $gt than "value"? how to make the $expr? thanks！
For embedded arrays - Use $arrayElemAt expression with dot notation to project last element.
db.col.find({$expr: {$gt: [{"$arrayElemAt": ["$array.field", -1]}, value]}})
db.collection.aggregate([
{
$match: {
$and: [
{ $expr: { $eq: [{ "$arrayElemAt": ["$fieldArray.name", -1] }, "value"] } },
{ $or: [] }
]
}
}
]);
In products collection, i have an Array of recentviews which has 2 fields viewedBy & viewedDate.
In a scenario if i already have a record with viewedby, then i need to update it. For e.g if i have array like this :-
"recentviews" : [
{
"viewedby" : "abc",
"vieweddate" : ISODate("2014-05-08T04:12:47.907Z")
}
]
And user is abc, so i need to update the above & if there is no record for abc i have to $push.
I have tried $set as follows :-
db.products.update( { _id: ObjectId("536c55bf9c8fb24c21000095") },
{ $set:
{ "recentviews":
{
viewedby: 'abc',
vieweddate: ISODate("2014-05-09T04:12:47.907Z")
}
}
}
)
The above query erases all my other elements in Array.
Actually doing what it seems like you say you are doing is not a singular operation, but I'll walk through the parts required in order to do this or otherwise cover other possible situations.
What you are looking for is in part the positional $ operator. You need part of your query to also "find" the element of the array you want.
db.products.update(
{
"_id": ObjectId("536c55bf9c8fb24c21000095"),
"recentviews.viewedby": "abc"
},
{
"$set": {
"recentviews.$.vieweddate": ISODate("2014-05-09T04:12:47.907Z")
}
}
)
So the $ stands for the matched position in the array so the update portion knows which item in the array to update. You can access individual fields of the document in the array or just specify the whole document to update at that position.
db.products.update(
{
"_id": ObjectId("536c55bf9c8fb24c21000095"),
"recentviews.viewedby": "abc"
},
{
"$set": {
"recentviews.$": {
"viewedby": "abc",
"vieweddate": ISODate("2014-05-09T04:12:47.907Z")
}
}
)
If the fields do not in fact change and you just want to insert a new array element if the exact same one does not exist, then you can use $addToSet
db.products.update(
{
"_id": ObjectId("536c55bf9c8fb24c21000095"),
"recentviews.viewedby": "abc"
},
{
$addToSet:{
"recentviews": {
"viewedby": "abc",
"vieweddate": ISODate("2014-05-09T04:12:47.907Z")
}
}
)
However if you are just looking for for "pushing" to an array by a singular key value if that does not exist then you need to do some more manual handling, by first seeing if the element in the array exists and then making the $push statement where it does not.
You get some help from the mongoose methods in doing this by tracking the number of documents affected by the update:
Product.update(
{
"_id": ObjectId("536c55bf9c8fb24c21000095"),
"recentviews.viewedby": "abc"
},
{
"$set": {
"recentviews.$": {
"viewedby": "abc",
"vieweddate": ISODate("2014-05-09T04:12:47.907Z")
}
},
function(err,numAffected) {
if (numAffected == 0) {
// Document not updated so you can push onto the array
Product.update(
{
"_id": ObjectId("536c55bf9c8fb24c21000095")
},
{
"$push": {
"recentviews": {
"viewedby": "abc",
"vieweddate": ISODate("2014-05-09T04:12:47.907Z")
}
}
},
function(err,numAffected) {
}
);
}
}
);
The only word of caution here is that there is a bit of an implementation change in the writeConcern messages from MongoDB 2.6 to earlier versions. Being unsure right now as to how the mongoose API actually implements the return of the numAffected argument in the callback the difference could mean something.
In prior versions, even if the data you sent in the initial update exactly matched an existing element and there was no real change required then the "modified" amount would be returned as 1 even though nothing was actually updated.
From MongoDB 2.6 the write concern response contains two parts. One part shows the modified document and the other shows the match. So while the match would be returned by the query portion matching an existing element, the actual modified document count would return as 0 if in fact there was no change required.
So depending on how the return number is actually implemented in mongoose, it might actually be safer to use the $addToSet operator on that inner update to make sure that if the reason for the zero affected documents was not just that the exact element already existed.