To store a new value in the Asterisk database, we use the Set() application,^[95] 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, we would 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.

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)
   same => n,Set(COUNT=${DB(test/count)})
   same => n,SayNumber(${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.

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.

There are an infinite number of ways to use the Asterisk database in a dialplan. To introduce the AstDB, we’ll look at 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). Therefore, we can use the ISNULL() function to verify whether or not a value was returned. 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=${DB(test/count)})
   same => n,GotoIf($[${ISNULL(${COUNT})}]?:continue)
   same => n,Set(DB(test/count)=1)
   same => n,Goto(1)
   same => n(continue),NoOp()

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

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

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

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

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

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