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MongoDB Aggregation Pipeline Operator to Convert String to date

In the world of MongoDB, seamless data management is key. Furthermore, handling dates stored as strings and the ability to convert them into the Date BSON type is a game-changer.

Today, we are going to explore different methods to achieve this.

Sample Data: A Glimpse Into the Task

Before we dive into the different methods, let’s take a quick look at a sample document in a MongoDB collection named “babies”:


{
"_id": 1,
"name": "Fetch",
"born": "2021-01-03T23:30:15.123"
}

Here the born field holds a date in string format. We will go through different techniques to convert this string into a proper Date BSON type.

Method 1: The $dateFromString Operator

MongoDB offers a dedicated aggregation pipeline operator, $dateFromString. It helps convert strings to dates. This operator takes a dateString argument. Let’s see it in action:

db.babies.aggregate([
{
$project: {
born: {
$dateFromString: {
dateString: '$born'
}
}
}
}
]);

Result:

{ "_id" : 1, "born" : ISODate("2021-01-03T23:30:15.123Z") }

Furthermore, the $dateFromString operator can accept other optional arguments.

Method 2: The $toDate Operator

Another useful pipeline operator is $toDate. It transforms various types into dates. Here’s how it works:

db.babies.aggregate([
{
$project: {
"born": {
$toDate: "$born"
}
}
}
]);

Result:

{ "_id" : 1, "born" : ISODate("2021-01-03T23:30:15.123Z") }

Method 3: The $convert Operator

For precise type conversions, MongoDB offers us the $convert operator. It has an input parameter specifying the field and a to parameter indicating the desired type.

db.babies.aggregate([
{
$project: {
result: {
$convert: {
input: "$born",
to: "date",
onError: "An error occurred",
onNull: "Input was null or empty"
}
}
}
}
]);

Result:

{ "_id" : 1, "result" : ISODate("2021-01-03T23:30:15.123Z") }

Method 4: Using the set Operator

For users on older MongoDB versions, the set operator can also get the job done. This method involves some manual steps, including iterating through the cursor and using the forEach() method:

var cursor = db.collection.find({"xyz": {"$exists": true, "$type": 2 }});
while (cursor.hasNext()) {
var doc = cursor.next();
db.collection.update(
{"_id": doc._id},
{"$set": {"xyz": new ISODate(doc.xyz)}}
);
}

Method 5: Leverage ClockTime

In some cases, we can use ClockTime along with the find() method for date conversions.

db.ClockTime.find().forEach(function(doc) {
doc.ClockInTime = new Date(doc.ClockInTime);
db.ClockTime.save(doc);
});

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Conclusion

In summary, our Support Techs demonstrated how to use Aggregation Pipeline operators to convert string to date in MongoDB.