Mongodb query specific month|year not date - mongodb

Question

How can I query a specific month in mongodb, not date range, I need month to make a list of customer birthday for current month.
In SQL will be something like that:
SELECT * FROM customer WHERE MONTH(bday)='09'
Now I need to translate that in mongodb.
Note: My dates are already saved in MongoDate type, I used this thinking that will be easy to work before but now I can't find easily how to do this simple thing.

Answer 1

With MongoDB 3.6 and newer, you can use the $expr operator in your find() query. This allows you to build query expressions that compare fields from the same document in a $match stage.
db.customer.find({ "$expr": { "$eq": [{ "$month": "$bday" }, 9] } })
For other MongoDB versions, consider running an aggregation pipeline that uses the $redact operator as it allows you to incorporate with a single pipeline, a functionality with $project to create a field that represents the month of a date field and $match to filter the documents
which match the given condition of the month being September.
In the above, $redact uses $cond tenary operator as means to provide the conditional expression that will create the system variable which does the redaction. The logical expression in $cond will check
for an equality of a date operator field with a given value, if that matches then $redact will return the documents using the $$KEEP system variable and discards otherwise using $$PRUNE.
Running the following pipeline should give you the desired result:
db.customer.aggregate([
{ "$match": { "bday": { "$exists": true } } },
{
"$redact": {
"$cond": [
{ "$eq": [{ "$month": "$bday" }, 9] },
"$$KEEP",
"$$PRUNE"
]
}
}
])
This is similar to a $project +$match combo but you'd need to then select all the rest of the fields that go into the pipeline:
db.customer.aggregate([
{ "$match": { "bday": { "$exists": true } } },
{
"$project": {
"month": { "$month": "$bday" },
"bday": 1,
"field1": 1,
"field2": 1,
.....
}
},
{ "$match": { "month": 9 } }
])
With another alternative, albeit slow query, using the find() method with $where as:
db.customer.find({ "$where": "this.bday.getMonth() === 8" })

Answer 2

You can do that using aggregate with the $month projection operator:
db.customer.aggregate([
{$project: {name: 1, month: {$month: '$bday'}}},
{$match: {month: 9}}
]);

Answer 3

First, you need to check whether the data type is in ISODate.
IF not you can change the data type as the following example.
db.collectionName.find().forEach(function(each_object_from_collection){each_object_from_collection.your_date_field=new ISODate(each_object_from_collection.your_date_field);db.collectionName.save(each_object_from_collection);})
Now you can find it in two ways
db.collectionName.find({ $expr: {
$eq: [{ $year: "$your_date_field" }, 2017]
}});
Or by aggregation
db.collectionName.aggregate([{$project: {field1_you_need_in_result: 1,field12_you_need_in_result: 1,your_year_variable: {$year: '$your_date_field'}, your_month_variable: {$month: '$your_date_field'}}},{$match: {your_year_variable:2017, your_month_variable: 3}}]);

Answer 4

Yes you can fetch this result within date like this ,
db.collection.find({
$expr: {
$and: [
{
"$eq": [
{
"$month": "$date"
},
3
]
},
{
"$eq": [
{
"$year": "$date"
},
2020
]
}
]
}
})

Answer 5

If you're concerned about efficiency, you may want to store the month data in a separate field within each document.