I have a collection like this
sample document
{
"field1":"one",
"field2":"two",
"field3":"three",
...some more key values
}
Now i have field value which is combination of field1, field2 and field3 values. i.e. for above document i have field = "onetwothree"
One option is to seggregate that field to 3 different fields but it is not possible because its pattern is not fixed
so I want to compare like this
db.collection.find({"filed1+field2+field3":field})
but it is not possible so one solution is to find all documents from collection and compare one by one but it is not optimized way to do this. So is it any better solution to do this?
Starting with MongoDB v3.6 you can run this query:
db.collection.find({
$expr: {
$eq: [
"onetwothree",
{ $concat: [ "$field1", "$field2", "$field3" ] }
]
}
})
Here's the documentation on $concat and $expr.
Related
I'm wanting to create an aggregation step to match documents where the value of a field in a document exists within an array in the same document.
In a very worked example (note this is very simplified; this will be fitting into a larger existing pipeline), given documents:
{
"_id":{"$oid":"61a9085af9733d0274c41990"},
"myArray":[
{"$oid":"61a9085af9733d0274c41991"},
{"$oid":"61a9085af9733d0274c41992"},
{"$oid":"61a9085af9733d0274c41993"}
],
"myField":{"$oid":"61a9085af9733d0274c41991"} // < In 'myArray' collection
}
and
{
"_id":{"$oid":"61a9085af9733d0274c41990"},
"myArray":[
{"$oid":"61a9085af9733d0274c41991"},
{"$oid":"61a9085af9733d0274c41992"},
{"$oid":"61a9085af9733d0274c41993"}
],
"myField":{"$oid":"61a9085af9733d0274c41994"} // < Not in 'myArray' collection
}
I want to match the first one because the value of myField exists in the collection, but not the second document.
It feels like this should be a really simple $elemMatch operation with an $eq operator, but I can't make it work and every example I've found uses literals. What I've got currently is below, and I've tried with various combinations of quotes and dollar signs round myField.
[{
$match: {
myArray: {
$elemMatch: {
$eq: '$this.myField'
}
}
}
}]
Am I doing something very obviously wrong? Is it not possible to use the value of a field in the same document with an $eq?
Hoping that someone can come along and point out where I'm being stupid :)
Thanks
You can simply do a $in in an aggregation pipeline.
db.collection.aggregate([
{
"$match": {
$expr: {
"$in": [
"$myField",
"$myArray"
]
}
}
}
])
Here is the Mongo playground for your reference.
I have a schema which has one field named ownerId and a field which is an array named participantIds. In the frontend users can select participants. I'm using these ids to filter documents by querying the participantIds with the $all operator and the list of participantsIds from the frontend. This is perfect except that the participantsIds in the document don't include the ownerId. I thought about using aggregate to add a new field which consists of a list like this one: [participantIds, ownerId] and then querying against this new field with $all and after that delete the field again since it isn't need in the frontend.
How would such a query look like or is there any better way to achieve this behavior? I'm really lost right now since I'm trying to implement this with mongo_dart for the last 3 hours.
This is how the schema looks like:
{
_id: ObjectId(),
title: 'Title of the Event',
startDate: '2020-09-09T00:00:00.000',
endDate: '2020-09-09T00:00:00.000',
startHour: 1,
durationHours: 1,
ownerId: '5f57ff55202b0e00065fbd10',
participantsIds: ['5f57ff55202b0e00065fbd14', '5f57ff55202b0e00065fbd15', '5f57ff55202b0e00065fbd13'],
classesIds: [],
categoriesIds: [],
roomsIds: [],
creationTime: '2020-09-10T16:42:14.966',
description: 'Some Desc'
}
Tl;dr I want to query documents with the $all operator on the participantsIds field but the ownerId should be included in this query.
What I want is instead of querying against:
participantsIds: ['5f57ff55202b0e00065fbd14', '5f57ff55202b0e00065fbd15', '5f57ff55202b0e00065fbd13']
I want to query against:
participantsIds: ['5f57ff55202b0e00065fbd14', '5f57ff55202b0e00065fbd15', '5f57ff55202b0e00065fbd13', '5f57ff55202b0e00065fbd10']
Having fun here, by the way, it's better to use Joe answer if you are doing the query frequently, or even better a "All" field on insertion.
Additional Notes: Use projection at the start/end, to get what you need
https://mongoplayground.net/p/UP_-IUGenGp
db.collection.aggregate([
{
"$addFields": {
"all": {
$setUnion: [
"$participantsIds",
[
"$ownerId"
]
]
}
}
},
{
$match: {
all: {
$all: [
"5f57ff55202b0e00065fbd14",
"5f57ff55202b0e00065fbd15",
"5f57ff55202b0e00065fbd13",
"5f57ff55202b0e00065fbd10"
]
}
}
}
])
Didn't fully understand what you want to do but maybe this helps:
db.collection.find({
ownerId: "5f57ff55202b0e00065fbd10",
participantsIds: {
$all: ['5f57ff55202b0e00065fbd14',
'5f57ff55202b0e00065fbd15',
'5f57ff55202b0e00065fbd13']
})
You could use the pipeline form of update to either add the owner to the participant list or add a new consolidated field:
db.collection.update({},[{$set:{
allParticipantsIds: {$setUnion: [
"$participantsIds",
["$ownerId"]
]}
}}])
I've got a mongodb aggregation pipeline with a $project stage and I'd like to include certain fields only if conditions are met. Specifically, I'd like to exclude the _id in one condition and include a second field 'second_id' in the other condition.
I know that it's not possible (yet) to exclude fields from a mongodb $project, but is it possible to conditionally include them?
Is there a way to conditionally exclude the _id field? It accepts a 0 or 1, but what if I want to determine that 0 or 1 based on an if statement. How would this be done?
Pseudocode for _id:
$project: { _id: { $ifNull: [ "$user_id", 0 ] } }
The main use of this would be to use the doc.user_id as the result _id, or allow mongodb to create a new autoincrement _id if that user_id is null.
There isn't a way currently to do this within the $project stage, but you can use the $redact stage to remove the field conditionally (i.e. you set the value to 0 like you are doing in your example.
db.collection.aggregate(
... matching and stuff ...
{$project: { _id: { $ifNull: [ "$user_id", 0 ] } }},
{$redact: {
{$cond: {
if: { $eq: [ "$user_id", 0 ] },
then: '$$PRUNE',
else: '$$DESCEND'
}}
}
I have a trick for this one:
"_id": {"$cond": [{"$eq": ["$user_id", null]}, "$nonExistinField", "$user_id"]}
Maybe this was not doable when the question was asked, but now it is.
There is a way to conditionally include/exclude a particular field in $project stage.
This can be achieved using $cond to evaluate your condition, and then return either '$true' or '$false'
{
myConditionalField:{$cond:{
if:{
$eq:['$some_field','some_value']
},
then:'$false',
else:'$true'
}}
}
Here, the field myConditionalField will be projected only if the value of some_field from previous stage matched some_value.
NOTE: Its assumed here that myConditionalField already exists from a previous stage. If it doesn't, then the else should be $some_field or whatever field you want to be projected.
Is there a way to do something like this on MongoDB?
select * from table where concat(field1, field2) = 'value'
To clarify, I have an array of full names, but the documents have firstname and lastname separate, so I want to do something like:
select * from table where concat(firstname, lastname) in ([ARRAY OF NAMES])
You can only do it with aggregation framework, not with regular find.
db.coll.aggregate({$project:{newField:{$concat:["$field1","$field2"]}}},
{$match:{newField:"value"}}
);
Note that this will not be able to use any indexes, since there is no support for indexes on computed values in MongoDB (yet).
If you have an index on field1 and you know how many characters you expect field1 to contribute to value you can improve performance of this aggregation like this:
db.coll.aggregate({$match:{field1:/^val/}},
{$project:{newField:{$concat:["$field1","$field2"]}}},
{$match:{newField:"value"}}
);
where val is first part of "value" string (you must not compare more characters than the shortest possible value of field1 though.
EDIT as of version 3.6 you can do this in find using the $expr expression:
db.coll.find({$expr:{$eq:["value", {$concat:["$field1", "$field2"]}]}})
If the argument ($field1 or $field2) resolves to a value of null or refers to a field that is missing, $concat returns null. Since mongoDB3.0, a new $ifNull is provided to check if the argument is null and provide an alternative
{ $ifNull: [ <expression>, <replacement-expression-if-null> ] }
db.coll.aggregate({$project:{newField:{$concat:[{$ifNull:["$field1",""]},{$ifNull:["$field2",""]}]}}},
{$match:{newField:"value"}})
The results may not differ if we are using $match, but this results will vary if you want to use $regex.
In Mongoose you can like that
let clause = [
{ $project: { name: { $concat: ["$first_name"," ","$last_name"]}}},
{ $match: { name: new RegExp("ab", 'i')}}
];
Model.aggregate(clause)
OutPut will be like that
[
{
"_id": "5911db2b9235272052fdd2e1",
"name": "Ali Abbas"
},
{
"_id": "5912f7dd8bdbc24aa37b5239",
"name": "Ali Abad"
},
{
"_id": "59229e0322abdb311818e419",
"name": "Syed Ali Abbas Shah"
},
{
"_id": "592837da188fa969cc135ddc",
"name": "Abu Akbar"
}
]
In MongoDB, is there any easy way to check Order of element in Array? For example I have a document like this:
{
_id: 1,
tags: ["mongodb", "rethinkdb", "couchbase", "others"]
}
I would like to check in tags field if mongodb come before rethinkdb or not(lets see in array element, mongodb=0, rethinkdb=1 index, so mongodb come first and our case match.)?
but if there is another document (like below) where rethinkdb comes before mongodb,It case does not match.
{
_id: 2,
tags: ["rethinkdb", "mongodb", "couchbase"]
}
Here mongodb(1) comes after rethinkdb(0) so our case does not match.
Your question is not really as clear as you think it is, and thus why there are several ways to answer it:
If you are looking just to find out if a document has "mongodb" as the first element of the array then you just issue a query like this:
db.collection.find({ "tags.0": "mongodb" })
And that will return only the documents that match the given value at the specified index position using "dot notation".
If you actually expect to match if an array is in an "expected order" then you can get some help from the aggregation pipeline and set operators that are available and other features in MongoDB 2.6:
db.collection.aggregate([
{ "$project": {
"$_id": "$$ROOT",
"matched": { "$setEquals": [
"$tags",
["mongodb", "rethinkdb", "couchbase", "others"]
]}
}},
{ "$match": { "matched": true }}
])
Or if your want is to make sure that the "mongodb" value comes before the "rethinkdb" value, then you will need to evaluate in JavaScript with mapReduce, or something equally not nice like the $where operator:
db.collection.find({
"$where": function() {
return this.tags.indexOf("mongodb") < this.tags.indexOf("rethinkdb");
}
})