Note: This project has officially moved here.

Cryptogram

Cryptogram is a DSL for authoring Cypher queries in Clojure.

Here's an example:

(require '[cryptogram :refer [start node where return]])

(start {:n (node [3 1])}
  (where (or (and (< :n.age 30) (= :n.name "Tobias"))
             (not (= :n.name "Tobias"))))
  (return :n))

and here's the query it generates:

START n = node(3, 1)
WHERE ((n.age < 30 and n.name = "Tobias") or not(n.name = "Tobias"))
RETURN n

Usage

For the sake of demonstration the examples will assume the following frowned upon practice is in play:

(use 'cryptogram)

But you're a better Clojure programmer than that.

Starting and returning

The most basic Cypher query begins with start and ends with return.

(start {:n "node(1)"}
  (return :n))

start is a macro that accepts a map of starting points, such as nodes or relationships, and the body of the query. In this case our starting point is the node with the id of 1 which is bound to n.

The body of our query consists soley of the return clause, which is simply a function which accepts any number of columns, or aggregates of, to return. With the execption of start, query clauses may be provided in any order.

The return value of start is a rendered Cypher query. A string. If we print the result of the above query we get:

START n = node(1)
RETURN n

Nodes and relationships

You may have noticed in our start map we used the string "node(1)" for our starting point. While strings are a nice "backdoor", Cryptogram provides the node and rel functions to make starting points more Clojure friendly.

node and rel, for all intents and purposes, are identical functions. The only difference is the strings they produce. Both accept a value, such as an integer or string, and optionally an index. The table below demonstrates the use of the node function and it's Cypher analogue.

Expression	Result
(node 1)	node(1)
(node [1 2 3])	node(1, 2, 3)
(node "foo")	node("foo")
(node :foo)	node("foo")
(node {:foo "bar"}	node(foo = "bar")
(node :nodes "name:A")	node:nodes("name:A")
(node :nodes {:foo "bar"})	node:nodes(foo = "bar")

With this we can now author queries like

START a = node(1), b = node(2)
RETURN a, b

completely with Clojure as

(start {:a (node 1) :b (node 2)}
  (return :a :b))

all while avoiding tedious and error prone string templating.

Match

One of the coolest features of the Cypher query language is MATCH. The MATCH clause allows you to (literally) draw out the relationships between nodes of interest in the graph.

Suppose we want to write the query

START bob = node(1)
MATCH bob-[:KNOWS]-alice
RETURN alice

with our DSL. Cryptogram provides the match function which allows you to compose MATCH patterns with one or more vectors. The example below demonstrates the use of match to create the query above.

(start {:bob (node 1)}
  (match [:bob [:KNOWS] :alice])
  (return :alice))

As you can see the syntax is very similar to the "real thing". However there are some differences.

The first thing that stands out about the above match pattern is the lack of - path symbols. When path symbols are omitted between elements a - symbol is assumed. So the basic "grammar" of a Cryptogram match pattern is

[:node-x path-symbol? :node-y ...]
[:node-x path-symbol? [:REL] path-symbol? :node-y ...]

where the string form of path-symbol is an element of the set #{"-", "--", "->", "<-", "-->", "<--"}.

Patterns may be of arbitrary length as in Cypher.

Emacs indention

If you're using Emacs with clojure-mode enabled you can place this in your init.el or evaluate it in the *scratch* buffer.

(define-clojure-indent
  (start* 'defun)
  (start 'defun))

License

Copyright © 2013 Joel Holdbrooks

Distributed under the Eclipse Public License, the same as Clojure.