Asterisk: The Future of Telephony, 2nd Edition

Using the Asterisk Database (AstDB)

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Asterisk provides a powerful mechanism for storing values called the Asterisk database (AstDB). The AstDB provides a simple way to store data for use within your dialplan.

Tip

For those of you with experience using relational databases such as PostgreSQL or MySQL, the Asterisk database is not a traditional relational database. It is a Berkeley DB Version 1 database. There are several ways to store data from Asterisk in a relational database. Check out Chapter 12 for a more about relational databases.

The Asterisk database stores its data in groupings called families, with values identified by keys. Within a family, a key may be used only once. For example, if we had a family called test, we could store only one value with a key called count. Each stored value must be associated with a family.

Storing Data in the AstDB

To store a new value in the Asterisk database, we use the Set() application,^[85] but instead of using it to set a channel variable, we use it to set an AstDB variable. For example, to assign the count key in the test family with the value of 1, write the following:

exten => 456,1,Set(DB(test/count)=1)

If a key named count already exists in the test family, its value will be overwritten with the new value. You can also store values from the Asterisk command line, by running the command database put family key value. For our example, you would type database put test count 1.

Retrieving Data from the AstDB

To retrieve a value from the Asterisk database and assign it to a variable, we use the Set() application again. Let’s retrieve the value of count (again, from the test family), assign it to a variable called COUNT, and then speak the value to the caller:

exten => 456,1,Set(DB(test/count)=1)
exten => 456,n,Set(COUNT=${DB(test/count)})
exten => 456,n,SayNumber(${COUNT})

You may also check the value of a given key from the Asterisk command line by running the command database get family key. To view the entire contents of the AstDB, use the database show command.

Deleting Data from the AstDB

There are two ways to delete data from the Asterisk database. To delete a key, you can use the DB_DELETE() application. It takes the path to the key as its arguments, like this:

; deletes the key and returns its value in one step
exten => 457,1,Verbose(0, The value was ${DB_DELETE(test/count)})

You can also delete an entire key family by using the DBdeltree() application. The DBdeltree() application takes a single argument―the name of the key family―to delete. To delete the entire test family, do the following:

exten => 457,1,DBdeltree(test)

To delete keys and key families from the AstDB via the command-line interface, use the database del key and database deltree family commands, respectively.

Using the AstDB in the Dialplan

There are an infinite number of ways to use the Asterisk database in a dialplan. To introduce the AstDB, we’ll show two simple examples. The first is a simple counting example to show that the Asterisk database is persistent (meaning that it survives system reboots). In the second example, we’ll use the BLACKLIST() function to evaluate whether or not a number is on the blacklist and should be blocked.

To begin the counting example, let’s first retrieve a number (the value of the count key) from the database and assign it to a variable named COUNT. If the key doesn’t exist, DB() will return NULL (no value). In order to verify if a value exists in the database or not, we will introduce the ISNULL() function that will verify whether a value was returned, and if not, we will initialize the AstDB with the Set() application, where we will set the value in the database to 1. The next priority will send us back to priority 1. This will happen the very first time we dial this extension:

exten => 678,1,Set(COUNT=${DB(test/count)})
exten => 678,n,GotoIf($[${ISNULL(${COUNT})}]?:continue)
exten => 678,n,Set(DB(test/count)=1)
exten => 678,n,Goto(1)
exten => 678,n(continue),NoOp()

Next, we’ll say the current value of COUNT, and then increment COUNT:

exten => 678,1,Set(COUNT=${DB(test/count)})
exten => 678,n,GotoIf($[${ISNULL(${COUNT})}]?:continue)
exten => 678,n,Set(DB(test/count)=1)
exten => 678,n,Goto(1)
exten => 678,n(continue),NoOp()
exten => 678,n,SayNumber(${COUNT})exten => 678,n,Set(COUNT=$[${COUNT} + 1])

Now that we’ve incremented COUNT, let’s put the new value back into the database. Remember that storing a value for an existing key overwrites the previous value:

exten => 678,1,Set(COUNT=${DB(test/count)})
exten => 678,n,GotoIf($[${ISNULL(${COUNT})}]?:continue)
exten => 678,n,Set(DB(test/count)=1)
exten => 678,n,Goto(1)
exten => 678,n(continue),NoOp()
exten => 678,n,SayNumber(${COUNT})
exten => 678,n,Set(COUNT=$[${COUNT} + 1])
exten => 678,n,Set(DB(test/count)=${COUNT})

Finally, we’ll loop back to the first priority. This way, the application will continue counting:

exten => 678,1,Set(COUNT=${DB(test/count)})
exten => 678,n,GotoIf($[${ISNULL(${COUNT})}]?:continue)
exten => 678,n,Set(DB(test/count)=1)
exten => 678,n,Goto(1)
exten => 678,n(continue),NoOp()
exten => 678,n,SayNumber(${COUNT})
exten => 678,n,Set(COUNT=$[${COUNT} + 1]
exten => 678,n,Set(DB(test/count)=${COUNT})
exten => 678,n,Goto(1)

Go ahead and try this example. Listen to it count for a while, and then hang up. When you dial this extension again, it should continue counting from where it left off. The value stored in the database will be persistent, even across a restart of Asterisk.

In the next example, we’ll create dialplan logic around the BLACKLIST() function, which checks to see if the current Caller ID number exists in the blacklist. (The blacklist is simply a family called blacklist in the AstDB.) If BLACKLIST() finds the number in the blacklist, it returns the value 1, otherwise it will return 0. We can use these values in combination with a GotoIf() to control whether the call will execute the Dial() application:

exten => 124,1,GotoIf($[${BLACKLIST()]?blocked,1)
exten => 124,n,Dial(${JOHN})

exten => blocked,1,Playback(privacy-you-are-blacklisted)
exten => blocked,n,Playback(vm-goodbye)
exten => blocked,n,Hangup()

To add a number to the blacklist, run the database put blacklist number 1 command from the Asterisk command-line interface.

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^[85] Previous versions of Asterisk had applications called DBput() and DBget() that were used to set values in and retrieve values from the AstDB. If you’re using an old version of Asterisk, you’ll want to use those applications instead.