MongoDB Collection management

Preamble

In the previous topics, the collection was created implicitly automatically when the first data were added to it. But we can also create it explicitly by using the db.createCollection(name, options) method, where name is the name of the collection and options is an optional object with additional initialization settings. For example:

Clearly creating a collection

db.createCollection("accounts")
{"ok" : 1}

Thus, a collection of accounts is created.

Renaming the collection

You may need to change the name of the collection while working. For example, if there was a misprint in the name of the collection when you first added data. And to avoid deleting and then recreating the collection, you should use the renameCollection function:

db.users.renameCollection("new_name")

And if the renaming goes well, the console will display:

{“ok” : 1}

Limited Edition Collections

When we send a request to the dd for selection, MongoDB returns us the documents in the order in which they were added. However, this order is not always guaranteed because the data can be deleted, moved, or changed.

That’s why MongoDB has a concept of a limited collection (capped collection). Such a collection guarantees that documents will be placed in the same order as they were added to the collection. The limited collections are of a fixed size. And when the collection is no longer in place, the oldest documents are removed and new data are added to the end.

Unlike ordinary collections, we can define limited collections explicitly. For example, we create a limited collection with the name profile and set its size to 9500 bytes:

db.createCollection("profile", {capped:true, size:9500})

And after the collection is successfully created, the console will display it:

{"ok":1}

You can also limit the number of documents in the collection by specifying it in the max parameter:

db.createCollection("profile", {capped:true, size:9500, max: 150})

However, in this way of creating the collection, you should take into account that if all the space for the collection is full (for example, the number of 9500 bytes allocated by us), and the number of documents has not reached the maximum, in this case, 150, then when adding a new document, the oldest document will be removed, and a new document will be inserted in its place.

When updating documents in such collections, one should remember that documents should not grow in size, otherwise the updating will not be possible.

It is also impossible to delete documents from such collections; you can only delete the whole collection.

MongoDB Sub-collections

We can use sub-collections to simplify data organization in collections. For example, the data for a user collection should be divided into profiles and credentials. And we can use db.users.profiles and db.users.accounts to create collections.

In doing so, they will not be in any way related to the user’s collection. That is, there will be three different collections, but in terms of the logical organization of data storage, it may be easier for someone.

Database, Collections, Documents: MongoDB

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