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+++
date = "2015-03-19T14:27:51-04:00"
title = "Collections"
[menu.main]
parent = "Tutorials"
identifier = "Collections"
weight = 30
pre = "<i class='fa'></i>"
+++
# Collections
MongoDB stores documents in collections. If a collection does not
exist, MongoDB creates the collection when you first store data for
that collection.
You can also explicitly create a collection with various options,
such as setting the maximum size or the documentation validation rules.
## Capped Collection
Capped collections have maximum size or document counts that prevent
them from growing beyond maximum thresholds. All capped collections must
specify a maximum size and may also specify a maximum document count.
MongoDB removes older documents if a collection reaches the maximum size
limit before it reaches the maximum document count.
To create a [capped collection](https://docs.mongodb.com/manual/core/capped-collections/),
use the ``createCollection`` method and specify ``'capped' : true``.
```js
{{% myproject-connect %}}
createCapped(db, function() {
client.close();
});
});
function createCapped(db, callback) {
db.createCollection("myCollection", { "capped": true, "size": 100000, "max": 5000},
function(err, results) {
console.log("Collection created.");
callback();
}
);
};
```
## Document Validation
Collections with [validation](https://docs.mongodb.com/manual/core/document-validation/)
compare each inserted or updated
document against the criteria specified in the validator option.
Depending on the ``validationLevel`` and ``validationAction``, MongoDB
either returns a warning, or refuses to insert or update the document
if it fails to meet the specified criteria.
The following example creates a ``contacts`` collection with a validator
that specifies that inserted or updated documents should match at
least one of three following conditions:
- the ``phone`` field is a string
- the ``email`` field matches the regular expression
- the ``status`` field is either ``Unknown`` or ``Incomplete``.
```js
{{% myproject-connect %}}
createValidated(db, function() {
client.close();
});
});
function createValidated(db, callback) {
db.createCollection("contacts",
{
'validator': { '$or':
[
{ 'phone': { '$type': "string" } },
{ 'email': { '$regex': /@mongodb\.com$/ } },
{ 'status': { '$in': [ "Unknown", "Incomplete" ] } }
]
}
},
function(err, results) {
console.log("Collection created.");
callback();
}
);
};
```
|
