Video Transcript (English)

Welcome! In this video, you’ll learn how to use common update operators in the MongoDB shell.

First, we’ll discuss the `updateOne()` method, which we’ll use with two common update operators, `$set` and `$push`. Then, we’ll go over how to use an option called `upsert`.

Let’s start with `updateOne()`. This method updates a single document. It accepts three arguments: a filter document, an update document, and an options object.

The first argument, the filter document, contains the selection criteria for the update.

The second argument, the update document, contains update operator expressions that will be used in the update.

The third argument is an options object. Note that `options` is not a required argument.

When updating documents, we can use operators like `$set` or `$push` with update methods like `updateOne()`.

The `$set` operator does one of two things: it adds new fields and values to a document, or

it replaces the value of a field with a specified value.

Likewise, the `$push` operator does one of two things:

It appends a value to an array, or if the field is absent, $push adds the array field with the value as its element

You can recognize an operator by the dollar sign preceding it.

Let's update some documents to observe this method in action.

Imagine that you manage a database called `audio` that contains a collection called `podcasts`.

You need to update a podcast document with a new subscriber count and host. You can use the `updateOne()` method and update operators to make these changes.

First, we’ll run a `findOne()` query so that we can view the podcast document. In the resulting document, the `subscribers` field is nonexistent, and the `hosts` array is empty.

We need to add a new `subscribers` field to the document. What operator can we use with `updateOne()` to do that?

`$set` is a perfect operator for this task because it can be used to add a new field and value to a document.

Within the `updateOne()` method of this example, we include the `_id` field in the filter document. The filter document contains the selection criteria for the update.

Next, we have our update document. It uses the $set operator as the field name to update the number of subscribers to 98562.

After running the `updateOne()` method, we receive an output message that shows the matched and modified document counts. This tells us that the update was a success.

If the update filter doesn’t match any documents, then no update occurs. In this case, we might want to create a document. This is what the `upsert` option allows us to do: insert a document with the provided information if matching documents don’t exist.

The `upsert` option is short for “update” or “insert.” When the filter that gets passed to the `updateOne()` method yields no matching documents, we can use `upsert` to insert a document with the provided information into the collection. In either case, the update operations provided in the update document will be carried out—either on the matched document, or on the document that was just inserted.

Let’s check out an example. We’ll use the `updateOne()` method to query a document that doesn’t exist in our database, and then we’ll examine the output.

After running this command without the `upsert` option, we get an output message showing that the matched count is 0, the modified count is 0, and the upserted count is 0.

This is expected, because the default behavior of `db.collection.updateOne()` is to perform the update only if a document matches the filter query.

Now let’s run the same query, but this time we’ll add `upsert:true` to our options object.

After passing in the filter document and the update document, we’ll use the options object. In options, we add `upsert: true`. This tells MongoDB to create a document if none are found by using the information provided in the query and update documents.

Notice that the output shows an upserted count of 1. This means that we have successfully inserted the document.

Excellent! Let’s move on to the `$push` operator.

Now that we’ve added the subscribers field, let’s go over how to add a new host to the “MongoDB Podcast” document.

The document currently contains an empty array for “hosts”. We’ll use the `$push` operator to add a new host to the array.

To do this, first pass in the filter. The filter includes the `_id` of the document that we want to update. Then, we pass in the update document, which includes the update modifiers that we want to apply. In this case, we’re using `$push` to add a host, Nic Raboy.

After running the command, you’ll be able to determine from the output that the document was modified. Specifically, the `matchedCount` and `modifiedCount` have a value of 1, which means that one document matched our filter, and that the same document was updated.

To confirm this, we can use `findOne`, which shows that our host was successfully added to the document. Awesome work!

Let’s recap what you learned in this video.

You learned how to use operators with the `updateOne()` method to modify your documents.

The $set operator adds a field and value to a document. `$set` can also be used to replace the value of a field with a specified value if that field already exists.

The `upsert` option allows you to insert documents with the provided information if matching documents don’t exist.

Finally, `$push` is used to add elements to an array.

There are additional update operators that you can explore in the MongoDB documentation.

Now you’re ready to start updating documents in MongoDB!