I have two collection present in mongodb database. one status column is common. I need matched and unmatched count from both the collection based on status column.
I have written some code but it fetching only matched count.
db.properties.aggregate([
{
$lookup: {
from: "old_properties_data",
localField: "identifier",
foreignField: "identifier",
as: "col2docs"
}
},
{"$group" : {_id:"_id", count:{$sum:1}}}
])
You can first $group by identifier to get the total match count. Then You can use uncorreleated subquery in $lookup to get the total size of old_properties_data. Finally do a $subtract to get the total unmatched count.
Here is the Mongo Playground for your reference.
Related
I am trying to delete orphaned documents in mongodb, which cross collections.
In the collection 'values', I have documents like this:
value:
{
resultId: <ObjectId>
...other data..
}
which reference documents in the collection 'results':
result:
{
_id: <ObjectId> //the resultId
}
A number of 'result' documents have been deleted, resulting in orphaned 'value' documents. How can I find all orphans and delete them?
What you will want to do is build up an aggregate pipeline and use the $lookup operator to fetch the corresponding result document. Then, add a $match operator to your aggregate pipeline to filter those that don't have corresponding result object.
db.values.aggregate([
{
$lookup: {
from: "results",
localField: "resultId",
foreignField: "id",
as: "resultDocument"
}
},
{ $match: { resultDocument: {$size:0} }}
])
This way, you have identified your orphaned documents and can delete them afterwards.
I have 2 collections as shown below:
branches
{
_id: ...,
custId: "abc123",
branchCode: "AA",
...other fields
}
branchHolidays
{
_id: ...,
custId: "abc123",
holidayDate: ISODate("2019-06-01T00:00:00:0000"),
holidayStatus: "PROCESSED",
..other fields
}
Need to get all branchHolidays with the custId available in branches collection along with the branchCode from branches collection. (branches.custId = branchHolidays.custId)
For the first part of join I tried the below query but I'm getting all the fields from branchHolidays collection.
db.getCollection('branchHolidays').aggregate([
{
$lookup: {
localField: "custId",
from: "branches",
foreignField: "custId",
as: "holidays"
}
},
$match: { holidayStatus: "PROCESSED" }
])
The above query returns all the documents from branchHolidays collection.
I'm new to mongo but I'm not able to figure out what the problem is. Have gone through most of the SO queries but haven't found anything which helped.
Note: There are multiple branchCodes mapped to 1 custId in branches collection.
The $lookup stage is similar to a left outer join. The sample aggregation should return all documents from the branchHolidays collection that have holidayStatus: "PROCESSED", and each document will have an added field holidays containing all documents from the branches collection that have the same custId. For those documents that do not match any braches, the holidays field will contain an empty array.
If you want to return only document that have matching branches, match on size, like:
holidays:{$not:{$size:0}}
Also note placing the $match: { holidayStatus: "PROCESSED" } before the $lookup will avoid querying the branches collection for documents that would be eliminated, which may improve performance.
I have a problem when querying mongoDB with nested objects notation:
db.messages.find( { headers : { From: "reservations#marriott.com" } } ).count()
0
db.messages.find( { 'headers.From': "reservations#marriott.com" } ).count()
5
I can't see what I am doing wrong. I am expecting nested object notation to return the same result as the dot notation query. Where am I wrong?
db.messages.find( { headers : { From: "reservations#marriott.com" } } )
This queries for documents where headers equals { From: ... }, i.e. contains no other fields.
db.messages.find( { 'headers.From': "reservations#marriott.com" } )
This only looks at the headers.From field, not affected by other fields contained in, or missing from, headers.
Dot-notation docs
Since there is a lot of confusion about queries MongoDB collection with sub-documents, I thought its worth to explain the above answers with examples:
First I have inserted only two objects in the collection namely: message as:
> db.messages.find().pretty()
{
"_id" : ObjectId("5cce8e417d2e7b3fe9c93c32"),
"headers" : {
"From" : "reservations#marriott.com"
}
}
{
"_id" : ObjectId("5cce8eb97d2e7b3fe9c93c33"),
"headers" : {
"From" : "reservations#marriott.com",
"To" : "kprasad.iitd#gmail.com"
}
}
>
So what is the result of query: db.messages.find({headers: {From: "reservations#marriott.com"} }).count()
It should be one because these queries for documents where headers equal to the object {From: "reservations#marriott.com"}, only i.e. contains no other fields or we should specify the entire sub-document as the value of a field.
So as per the answer from #Edmondo1984
Equality matches within sub-documents select documents if the subdocument matches exactly the specified sub-document, including the field order.
From the above statements, what is the below query result should be?
> db.messages.find({headers: {To: "kprasad.iitd#gmail.com", From: "reservations#marriott.com"} }).count()
0
And what if we will change the order of From and To i.e same as sub-documents of second documents?
> db.messages.find({headers: {From: "reservations#marriott.com", To: "kprasad.iitd#gmail.com"} }).count()
1
so, it matches exactly the specified sub-document, including the field order.
For using dot operator, I think it is very clear for every one. Let's see the result of below query:
> db.messages.find( { 'headers.From': "reservations#marriott.com" } ).count()
2
I hope these explanations with the above example will make someone more clarity on find query with sub-documents.
The two query mechanism work in different ways, as suggested in the docs at the section Subdocuments:
When the field holds an embedded document (i.e, subdocument), you can either specify the entire subdocument as the value of a field, or “reach into” the subdocument using dot notation, to specify values for individual fields in the subdocument:
Equality matches within subdocuments select documents if the subdocument matches exactly the specified subdocument, including the field order.
In the following example, the query matches all documents where the value of the field producer is a subdocument that contains only the field company with the value 'ABC123' and the field address with the value '123 Street', in the exact order:
db.inventory.find( {
producer: {
company: 'ABC123',
address: '123 Street'
}
});
I have two collections, one that has _id and UserId, and another that has UserId (same unique identifier) and "other data".
I want to filter the latter collection based on a list of _ids from the former collection.
Can someone provide an example query for this scenario?
The only way to 'join' collections in MongoDB is a $lookup aggregation stage (available in version 3.2).
firstCollection.aggregate([
{ $match: { _id: {$in: [1,2,3] }}}, // filter by _ids
{
$lookup:
{
from: "secondCollection",
localField: "UserId",
foreignField: "UserId",
as: "data"
}
}
])
That will add 'data' field to the documents from the first collection which will contain all related documents from second collection. If relation is not 1:1, you can add $unwind stage to flatten results:
{$unwind: "$data"}
I have a scenario in spring-mongo query. Mongo version is 3.2
Application have two collections (Collection A and Collection B).
**Sample contents**
Collection A :: {"_id":1, "name":"content 1"}...{"_id":100, "name":"content 100"}
Collection B :: {"_id":1, "name":"parent 1", "a":[1,2,58,67]}
{"_id":2, "name":"parent 2", "a":[2,85,96,99]}
Collection B holds reference ids of Collection A as a array.
Scenario:
I will past list of ids of Collection A to the query: I need to get list of ids of Collection A which are not associated anywhere in Collection B.
how to achieve this?
I am planning to proceed with Aggregation with following query.. Looking up with
preserveNullAndEmptyArrays saving my day.
db.a.aggregate([
{
$match: { "_id":{$in:["1","5","10"]} }
},
{
$lookup:
{
from: "b",
localField: "_id",
foreignField: "a",
as: "moneyid"
}
},
{
$unwind:
{"path":"$moneyid", "preserveNullAndEmptyArrays":true}
},
{
$match:{
"moneyid":{$eq:null}
}
}
])
It can be done using the following approach
1) Find Unique Id's in Collection B which are in array "a":[]
2) Execute a find query in Collection A - Use $nin in the find query and pass all the ids which you obtained from array "a":[] from Collection B
Note:If you need to find matching documents between two collections then you can use $lookup which works like a left outer join.