Database Reference
In-Depth Information
The
drop()
function returns either
true
or
false
, depending on whether the
operation has completed successfully. Likewise, if you want to remove an entire database
from MongoDB, you can use the
dropDatabase()
function, as in this example:
> db.dropDatabase()
{ "dropped" : "library", "ok" : 1 }
Note that this snippet will remove the database you are currently working in (again,
be sure to check
db
to see which database is your current database).
Referencing a Database
At this point, you have an empty database again. You're also familiar with inserting
various kinds of data into a collection. Now you're ready to take things a step further and
learn about
database
referencing
. As you've already seen, there are plenty of scenarios
where embedding data into your document will suffice for your application (such as the
track list or the list of authors in the topic entry). However, sometimes you do need to
reference information in another document. The following sections will explain how to go
about doing so.
Just as with SQL, references between documents in MongoDB are resolved by
performing additional queries on the server. MongoDB gives you two ways to accomplish
this: referencing them manually or using the DBRef standard, which many drivers also
support.
Referencing Data Manually
The simplest and most straightforward way to reference data is to do so manually. When
referencing data manually, you store the value from the
_id
of the other document in
your document, either through the full ID or through a simpler common term. Before
proceeding with an example, let's add a new document and specify the publisher's
information in it (pay close attention to the
_id
field:
> apress = ( { "_id" : "Apress", "Type" : "Technical Publisher", "Category"
:
["IT", "Software","Programming"] } )
{
"_id" : "Apress",
"Type" : "Technical Publisher",
"Category" : [
"IT",
"Software",
"Programming"
]
}
> db.publisherscollection.insert(apress)
