In my documents, the decimal values are stored as String ( Because of my BigDecimal in Java converted to String). This is perfectly OK and required when I am looking one document at a time. However, I require them to be treated as Double during aggregation purpose (for e.g., $sum).
Is there a way so that I can covert the String to Double during $project operation (or otherwise) during my aggregation pipeline. So that my successive pipelines will do $sum on the Double field.
I am not considering the option of storing them as Double, as I would need to preserve the precision per document basis, but I am OKif the precision is lost during my aggregation operation.
There is no operator to do conversions in aggregation pipeline. Is it possible to store two different values one as BigDecimal / String and another as a double / float value? That can be one of quick and dirty option if you are ok to ignore the flakiness due to the floating point values.
You can use $toDouble, which is essentially a short hand for $convert with to: "double"
Assume we have a document;
{
"str": "3.66"
}
and to convert the string value to double;
db.collection.aggregate([
{
$addFields: {
double: {
$toDouble: "$str"
}
}
}
])
will result in;
{
"str": "3.66",
"double": 3.66
}
Where it can be used by other stages of aggregation pipeline.
Check on Mongo Playground
Mongodb version 4.0 introduced the $toInt operator in the aggregation pipeline. You can use that to convert easily from string to number.
Link to documentation: https://docs.mongodb.com/manual/reference/operator/aggregation/toInt/
Related
I have a document (inside aggregation, after $group stage) which have an object (but I could form array, if I needed it to) with number values.
MongoPlayground example with data and my aggregate query available here.
And I want to make a new _id field during next $project stage, consisted of this three number values, like:
item_id | unix time | pointer
_id: 453435-41464556645#1829
The problem is, that when I am trying to use $concat, the query returns me an error like:
$concat only supports strings, not int
So here is my question: is it possible to achieve such results? I have seen the relevant question MongoDB concatenate strings from two fields into a third field, but it didn't cover my case.
The $concat only concatenate strings, these fields $_id.item_id contains int value and $_id.last_modified double value,
The $toString converts a value to a string,
_id: {
$concat: [
{
$toString: "$_id.item_id"
},
" - ",
{
$toString: "$_id.last_modified"
}
]
}
Playground: https://mongoplayground.net/p/SSlXW4gIs_X
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.
how to print field and length of this field
e.g. I have {name:"aaa"} document is collection "names"
then the expected output is
{name:"aaa", name_legth:3}
Please help.
MongoDB versions <3.2 don't have a text aggregation operator to compute length of a string value stored in a field. If you are using version 3.2 or older, you will need to implement the length computation outside the DB (such as in the controller layer of an MVC architecture).
Version 3.4, though, includes several new and useful aggregation operators including the $strLenCP operator which should serve your purpose. The usage for your case would be as follows:
db.names.aggregate(
[
{
$project: {
"name": 1,
"name_length": { $strLenCP: "$name" }
}
}
]
)
The documentation for the aggregation operator can be found here.
I am trying to perform an aggregation query on a collection. I want to divide 2 of the fields and check if this is less than a certain value.
The way this db was made, it has all the fields as strings, and this isn't something I can really change right now. I wondered if there was a way to cast the values as numbers, maybe using $let or something?
As it is I currently get the error
exception: $divide only supports numeric types, not String and String
This is an example of the sort of query I am trying to run:
db.myCollection.aggregate([{
"$project": {
"mins": {
"$divide": ["$ALOWOVRLTOTL", "$FEESCALLCOST"]}
}
},
"$match": {
"mins": {
"$lte": 40
}
}
}])
You won't be able to perform the divide operation on non-numerical values. A possible solution to this would be to run an update and parse the String values to a numerical value.
Have a look at this question:
how to convert string to numerical values in mongodb
When I have two MongoDB documents like this...
db.test.insert( {"value" : "10123"} );
db.test.insert( {"value" : "160"} );
The result of a query like:
db.test.find({"value" :{$gt : "12"} });
is..
{ "_id" : ObjectId("4c6d1b92304326161b678b89"), "value" : "160" }
It's obvious, that a string comparison is made, so that my first value is not returned.
Is there any way to cast within the query?
Something like:
db.test.find({ (int) "value" :{$gt : 12} });
would be great. A query like
db.test.find({"value" :{$gt : 12} }); // without the quotes around "12"
returns nothing.
You can use the following JavaScript expression:
db.test.find("this.value > 12")
This uses JavaScript's automatic conversion from string to number.
I have a similar workaround, i find that if you can use the mongo shell, you can write an statement to do this in javascript, but capable of using indexes.
var myItems = []
var it = db.test.find({},{value:1})
while (it.hasNext()){
var item = it.next();
if(parseInt(item.value) > 12)
myItems.push(item);
}
If you want this to run faster than previus solution, you have to ensure the index on the value field.
Type casting in MongoDB is available after version >= 4.0. Check MongoDB's aggregation operator $convert and similar operators. Since you wanted to convert string to int you can use $toInt:
db.collection.find({ $expr: { $gt: [ { $toInt: "$value" }, 12 ] } })
Test : mongoplayground
Note :
Here we're converting value which is a string field to int on the fly & Since it got converted to int - we're comparing it to input of type int. Your output documents will still have original type for value field which is string (we're not actually changing type in response docs, if needed use aggregation & it's stage $project to see int values for field value in response docs).
Since we're using aggregation operators in .find() we need to wrap everything in $expr.
Even though this is pretty common nowadays & is easy to do, but remember we're casting string to int on every Read, rather if you can take care of this on Writes or Updates it would be easy & more efficient.
To convert String into int use this
db.test.find({'year': {$type: 2}}).forEach(
function (x) {
x.value=new NumberInt(x.value);
db.test.save(x)}
)
And after that you can directly query like :
db.test.find({"value" :{$gt : 12} });
$gt wasn't set for this use case. You would have to use regex for strings. Probably easier to just create a new field with the number as a number.