This is a similar question to $and query returns no result, however the answer there does not apply in this case.
I have the following query:
{
$and: [
{
ownerId: "505b832c975a5c3ca6e9523b"
},
{
privacyLevel: "Public"
}
]
}
My collection has 16 documents, all of which are "Public" and 7 of which have the ownerId above. The subqueries behave correctly and return the correct documents so I would expect 7 results from this query.
The $and query returns nothing, I am at a loss as to why that might be.
If you are just querying two fields you do not need an $and operator. Your query will simply be:
.find({ownerId: "505b832c975a5c3ca6e9523b", privacyLevel: "Public"})
Related
When I'm trying to query for several categories in a database, such as:
Example: {
"AttributeA": type,
"AttributeB": type,
"AttributeC": type,
"AttributeD": type
etc...
}
And say that I'm trying to query for samples that have (AttributeA matching criteria1 or AttributeB matching criteria2) and (AttributeC matching criteria3, 4, 5, or 6). How would we compose the .find() method in MongoDB to match without error or complicated boolean algebra (distributing out the "and")?
I've tried using notation such as:
db.Example.find({
$or:[{"AttributeA" : criteria1, "AttributeB" : criteria2}],
$or:[{"AttributeC" : criteria3, "AttributeC" : criteria4, ...}]
})
in an attempt for an easy query satisfying the conditions above, but in some cases this would result in only one condition of the query being satisfied (giving a "duplicate key '$or'" warning before compiling) and in other instances (different platforms) this straight up gives an error along the lines of the warning.
If I understood the question correctly, I think you are looking for a query predicate such as:
{
$or: [
{
AttributeA: "criteria1"
},
{
AttributeB: "criteria2"
}
],
AttributeC: {
$in: [
"criteria3",
"criteria4",
"criteria5"
]
}
}
See how it works on this playground example
How would we compose the .find() method in MongoDB to match without ... complicated boolean algebra (distributing out the "and")?
By default, MongoDB applies an implicit $and operator to query predicates at the same level. There is an explicit operator also available, but it is not needed in your situation. You can allow the database to distribute the condition(s) that is logically $anded for you.
AttributeC matching criteria3, 4, 5, or 6
This is a perfect use for the $in operator, which I've used in the query above as:
AttributeC: {
$in: [ "criteria3", "criteria4", "criteria5" ]
}
select records using aggregate:
db.getCollection('stock_records').aggregate(
[
{
"$project": {
"info.created_date": 1,
"info.store_id": 1,
"info.store_name": 1,
"_id": 1
}
},
{
"$match": {
"$and": [
{
"info.store_id": "563dcf3465512285781608802a"
},
{
"info.created_date": {
$gt: ISODate("2021-07-18T21:07:42.313+00:00")
}
}
]
}
}
])
select records using find:
db.getCollection('stock_records').find(
{
'info.store_id':'563dcf3465512285781608802a',
'info.created_date':{ $gt:ISODate('2021-07-18T21:07:42.313+00:00')}
})
What is difference between these queries and which is best for select by id and date condition?
I think your question should be rephrased to "what's the difference between find and aggregate".
Before I dive into that I will say that both commands are similar and will perform generally the same at scale. If you want specific differences is that you did not add a project option to your find query so it will return the full document.
Regarding which is better, generally speaking unless you need a specific aggregation operator it's best to use find instead, it performs better
Now why is the aggregation framework performance "worse"? it's simple. it just does "more".
Any pipeline stage needs aggregation to fetch the BSON for the document then convert them to internal objects in the pipeline for processing - then at the end of the pipeline they are converted back to BSON and sent to the client.
This, especially for large queries has a very significant overhead compared to a find where the BSON is just sent back to the client.
Because of this, if you could execute your aggregation as a find query, you should.
Aggregation is slower than find.
In your example, Aggregation
In the first stage, you are returning all the documents with projected fields
For example, if your collection has 1000 documents, you are returning all 1000 documents each having specified projection fields. This will impact the performance of your query.
Now in the second stage, You are filtering the documents that match the query filter.
For example, out of 1000 documents from the stage 1 you select only few documents
In your example, find
First, you are filtering the documents that match the query filter.
For example, if your collection has 1000 documents, you are returning only the documents that match the query condition.
Here You did not specify the fields to return in the documents that match the query filter. Therefore the returned documents will have all fields.
You can use projection in find, instead of using aggregation
db.getCollection('stock_records').find(
{
'info.store_id': '563dcf3465512285781608802a',
'info.created_date': {
$gt: ISODate('2021-07-18T21:07:42.313+00:00')
}
},
{
"info.created_date": 1,
"info.store_id": 1,
"info.store_name": 1,
"_id": 1
}
)
I cant spot what the issue here is. This returns nothing
db.mycoll.aggregate([
{$project:{CreatedAt:"$CreatedAt",Now:"$$NOW",DateFloor:{$add:["$$NOW",-24*60*60000]}}},
{$match:{CreatedAt:{$gte:"$DateFloor"}}}
])
But this returns results - substituting DateFloor with actual value
db.mycoll.aggregate([
{$project:{CreatedAt:"$CreatedAt",Now:"$$NOW",DateFloor:{$add:["$$NOW",-24*60*60000]}}},
{$match:{CreatedAt:{$gte: ISODate("2020-04-28T23:17:56.547Z")}}}
])
Issue with your query is when you're doing :
{$match:{CreatedAt:{$gte:"$DateFloor"}}}
You're actually checking for documents where CreatedAt field's value to be greater than input string value "$DateFloor", So $match is not considering "$DateFloor" as another field in the same document rather it's considering it as a string value. So to compare two fields from same document you need to use $gte with $expr (which will let you use aggregation expressions within the query language).
{
$match: {
{
$expr: {
$gte: ["$CreatedAt", "$DateFloor"];
}
}
}
}
So you might get confused when I say aggregation expressions & why $gte needs to be wrapped inside $expr - In your actual query $gte refers to comparison operator in MongoDB but in this above query $gte refers to aggregation pipeline operator where both technically does the same but which is what needed to compare two fields from same document.
Can anyone tell me how to add a $match stage to an aggregation pipeline to filter for where a field MATCHES a query, (and may have other data in it too), rather than limiting results to entries where the field EQUALS the query?
The query specification...
var query = {hello:"world"};
...can be used to retrieve the following documents using the find() operation of MongoDb's native node driver, where the query 'map' is interpreted as a match...
{hello:"world"}
{hello:"world", extra:"data"}
...like...
collection.find(query);
The same query map can also be interpreted as a match when used with $elemMatch to retrieve documents with matching entries contained in arrays like these documents...
{
greetings:[
{hello:"world"},
]
}
{
greetings:[
{hello:"world", extra:"data"},
]
}
{
greetings:[
{hello:"world"},
{aloha:"mars"},
]
}
...using an invocation like [PIPELINE1] ...
collection.aggregate([
{$match:{greetings:{$elemMatch:query}}},
]).toArray()
However, trying to get a list of the matching greetings with unwind [PIPELINE2] ...
collection.aggregate([
{$match:{greetings:{$elemMatch:query}}},
{$unwind:"$greetings"},
]).toArray()
...produces all the array entries inside the documents with any matching entries, including the entries which don't match (simplified result)...
[
{greetings:{hello:"world"}},
{greetings:{hello:"world", extra:"data"}},
{greetings:{hello:"world"}},
{greetings:{aloha:"mars"}},
]
I have been trying to add a second match stage, but I was surprised to find that it limited results only to those where the greetings field EQUALS the query, rather than where it MATCHES the query [PIPELINE3].
collection.aggregate([
{$match:{greetings:{$elemMatch:query}}},
{$unwind:"$greetings"},
{$match:{greetings:query}},
]).toArray()
Unfortunately PIPELINE3 produces only the following entries, excluding the matching hello world entry with the extra:"data", since that entry is not strictly 'equal' to the query (simplified result)...
[
{greetings:{hello:"world"}},
{greetings:{hello:"world"}},
]
...where what I need as the result is rather...
[
{greetings:{hello:"world"}},
{greetings:{hello:"world"}},
{greetings:{"hello":"world","extra":"data"}
]
How can I add a second $match stage to PIPELINE2, to filter for where the greetings field MATCHES the query, (and may have other data in it too), rather than limiting results to entries where the greetings field EQUALS the query?
What you're seeing in the results is correct. Your approach is a bit wrong. If you want the results you're expecting, then you should use this approach:
collection.aggregate([
{$match:{greetings:{$elemMatch:query}}},
{$unwind:"$greetings"},
{$match:{"greetings.hello":"world"}},
]).toArray()
With this, you should get the following output:
[
{greetings:{hello:"world"}},
{greetings:{hello:"world"}},
{greetings:{"hello":"world","extra":"data"}
]
Whenever you're using aggregation in MongoDB and want to create an aggregation pipeline that yields documents you expect, you should always start your query with the first stage. And then eventually add stages to monitor the outputs from subsequent stages.
The output of your $unwind stage would be:
[{
greetings:{hello:"world"}
},
{
greetings:{hello:"world", extra:"data"}
},
{
greetings:{hello:"world"}
},
{
greetings:{aloha:"mars"}
}]
Now if we include the third stage that you used, then it would match for greetings key that have a value {hello:"world"} and with that exact value, it would find only two documents in the pipeline. So you would only be getting:
{ "greetings" : { "hello" : "world" } }
{ "greetings" : { "hello" : "world" } }
In MongoDB i have to give OR condition in WHERE clause
I am a beginner. I dont know how to acheive this?
DELETE FROM tablename WHERE id = 6 OR id =8
What is the similar query in MongoDB??
Just use the $or operator as described here.
db.tablename.remove({ $or: [ { _id: 6 }, { _id: 8 } ] })
You may also find the appropriate section in the manual for SQL comparison useful.