simple user query language

suql is a small language for writing simple data queries. The intended use case is to give users of a web application the ability to perform predicate-based filtering on a table, similar to JQL for JIRA. suql has an interpreter that lets it query collections of Scala objects, and also a compiler that converts the suql code to a SQL or MongoDB query.

Language features

• Everything is an expression, and a query is a single expression
• Equality and order comparisons (=, !=, >, <)
• Logical negation (!) and boolean operators (&&, ||)

The language deliberately omits a few features to maximise security, simplicity and portability.

• No variables
• No user-defined functions
• No ability to assign, write or update data - purely read-only

An example: querying countries

Let's say we have a table of countries, like so:

country.name	country.continent	country.population
United Kingdom	Europe	64100000
France	Europe	66030000
United States	North America	316500000
...	...	...

If we want to query all of the countries in Europe - the query would look like this:

country.continent = "Europe"

Boolean logic allows us to write more complicated queries, like this:

country.continent = "North America" && country.population > 100000000

Parentheses can be used to disambiguate expressions:

(country.continent = "North America") && (country.population > 100000000)

This example shows how to perform a query from Scala code:

case class Country(name: String, continent: String, population: Int)

val countries = List(
  Country("United Kingdom", "Europe", 64100000),
  Country("France", "Europe", 66030000),
  Country("United States", "North America", 316500000)
)

val collectionQuery: CollectionQuery = new CollectionQuery
val bigCountriesInNorthAmerica = collectionQuery.query("country.continent = \"North America\" && country.population > 100000000", testCountries)

Adding targets

To write a new code generation target, implement the CodeGenerator trait. An example, which turns a suql syntax tree back into suql code, is implemented in the Uncompiler class.