Example 2: Phonebook

We have covered a lot of ground so far. Let’s consolidate our knowledge by building a simple application, using all the concepts we’ve learned so far.

We’ll build a simple phonebook application. Here is a the brief:

Phonebook requirements

Create a simple HTTP service to represent a phone book.

Acceptance criteria. - List all entries in the phone book. - Create a new entry to the phone book. - Remove an existing entry in the phone book. - Update an existing entry in the phone book. - Search for entries in the phone book by surname.

A phone book entry must contain the following details: - Surname - Firstname - Phone number - Address (optional)

The database

Create a new namespace called phonebook.db.

(ns phonebook.db)

We’ll create a database constructor, and some functions to access its contents.

This constructor creates a map with two entries, both refs. We could use an atom, but refs offer more flexibility.

(defn create-db [entries]
  {:phonebook (ref entries)
   :next-entry (ref (inc (apply max (keys entries))))})

Now let’s add some code to add an entry.

(defn add-entry [db entry]
  (dosync
   (let [nextval @(:next-entry db)]
     (alter (:phonebook db) conj [nextval entry])
     (alter (:next-entry db) inc)
     nextval)))

Creating new phonebook entries

For this requirement, we are going to support the POST method.

Let’s add the following entry to the static properties of the IndexResource.

{:parameters {:post {:form {:surname String
                           :firstname String
                           :phone [String]}}}
…
}

This declaration tells yada what parameters we are expecting in the POST method. In return, yada will do the following:

Validate the request, ensuring that all the mandatory parameters have been provided
Coerce the parameters to the desired types (if possible).
Return a 400 response (if not).
Parse the request body.
Help prevent XSS scripting attacks, by ensuring that no unexpected parameters are allowed to pass through. We should still be careful of String parameters though.