Études for Erlang

Étude 10-2: Using Mnesia

I have good news and bad news. First, the bad news. Mnesia is not a relational detabase management system. If you try to use a query list comprehension to join three tables, Erlang will complain that joins with more than two tables are not efficient.

Now, the good news. While trying to find a way around this, I discovered something about query list comprehensions that is really pretty neat, and I’m happy to share it with you.

In this étude, you will use add a table of customer names and use Mnesia query list comprehensions to join data from those tables when producing a summary.

Part One

You will need to add a record for customers to phone_records.hrl. Its fields will be:

• Phone Number (this is the key)
• Customer’s last name
• Customer’s first name
• Customer’s middle name
• Rate paid per minute (float)

Again, you may name the record whatever you wish, and you may use any field names you wish.

Part Two

In a module named phone_mnesia, create the Mnesia tables for the two files. The function that does this will be named setup/2, and its arguments will be the names of the file containing the data.

Use the phone call data from Étude 10-1, and use this data for the customers. Put it in a file named customer_data.csv or whatever other name you wish.

213-555-0172,Nakamura,Noriko,,0.12 301-555-0433,Ekberg,Erik,Engvald,0.07 415-555-7871,Alvarez,Alberto,Agulto,0.15 650-555-3326,Girard,Georges,Gaston,0.10 729-555-8855,Tran,Truong,Thai,0.09 838-555-1099,Smith,Samuel,Steven,0.10 ...