Get Started with MongoDB
Update Mongo Documents using updateOne, updateMany, $set and $unset operations
In this lesson, we learn that updating documents in MongoDB involves using the updateOne and updateMany methods along with operators like $set and $unset.
The $set operator allows us to modify existing properties or add new ones, even in nested structures, while the $unset operator removes specified properties from a document.
We demonstrate how to use these operators to change a document's salary, modify nested personal information, and remove fields like position.
We also show how to combine $set and $unset in a single operation for efficient data management.
[00:00] In order to update documents in a MongoDB collection, we can use the updateMany and updateOne methods. So updateOne is going to, of course, update at most one matched document and updateMany, potentially many. Now they're both similar in a way that the first argument that we're going to pass here is the query which defines what are the documents that we want to update and the second one is going to determine what are the changes, what should change within the document's data. So before we change anything, let's search for a single object that we're going to actually modify. So let's find a document that will have the name which is Bob Johnson.
[00:44] Now let's see what this is And we've got the ID and name, position, age, and other properties. So let's start with modifying actually what is going to be, let's use update one, the salary within this document. So what we would normally do is that we would push that, hey, salary is going to be, let's say 20K from now on, but in MongoDB, we need to explicitly determine what is the operation that we want to apply here. So it's not clear in a way, like what is going to be the operation over here like it could be setting but it could also be incrementing so it's not clear this way so we need to specify explicitly that this is going to be a setter So it doesn't matter what it used to be before, we're going to set it to this value. And of course, this operator starts with the dollar sign.
[01:37] Here we can see that it's been acknowledged, there were no inserted IDs, so no new documents. There was one matched count using this query over here. So this one determines the match and how many of them were modified. Absorption is a slightly different operation that we're going to get into slightly later. So let's see that our document with name Bob Johnson has salary 20k.
[02:01] So let's see what else can we do. So set allows us to modify one or more properties. And if we wanted to modify something that is nested such as personal info, we can achieve that using again, what is the string, which basically concatenates the properties with the dots and here we can pass literally whatever we want and again matched one modified one let's see what is the result we can see that the nested property has been updated Now what's also interesting is that the same way we can add properties or even add nested properties. So the thing that we're doing over here is that we would like to add a C property on an object that lives under B and again lives under A and A doesn't exist yet so the whole structure is going to be added on the fly. So let's also see this one and we can see that there is a nested structure being created.
[03:01] So this is set. Now let's see the inverse operation which is going to be on set. Now if we do the on set like we don't really care what is going to be the value here but just due to make it consistent we need to again reproduce the object structure and here like this value here is irrelevant but we need to stick to the syntax to the structure so that there is a key and value. So if we run this one, then the C property is going to be removed, since what we have removed in our operation is actually not A, not B, but just C. So if we want to remove a slightly bigger part, then what we can see is just to start removing with a and this way we can drop the whole part over here so let's run it and let's see what has changed so a b c like neither of them exists anymore So let's also redo the very same operation again.
[04:06] So after doing this unset over here, the only thing that has changed is that there is one matched document, the same way as before, because we are using the same query over and over again, but there are no modified documents. Since applying this change set into this document would result in no changes. So here we can also see how many documents have been changed. It's also possible to run two different updates at the same time. So we can merge the set and unset.
[04:36] So let's use the set over here and let's say that we're going to set the name to or maybe the age to make it 60 and to unset the A or maybe we can remove the position just to see that something has actually changed. So one was matched, one was modified and let's also find Bob Johnson so we can see that age is changed, position is removed, so both changes have been applied using a single execution.