Quaere: LINQ Arrives for Java

Anders Noras introduced the Quaere library, billed as LINQ for Java, last week at JavaZone. Quaere is a DSL providing query functionality against any structure implementing Iterable or its Queryable interface.

Noras lists the features of Quaere:

• Ability to perform queries against arrays or data structure implementing the Iterable interface.
• An internal DSL (based on static imports and fluent interfaces) that lets you integrate the query language with regular Java code. No preprocessing or code generation steps are required to use the DSL, simply add a reference to the quaere.jar file (and its dependencies).
• A large number of querying operators including restriction, selection, projection, set, partitioning, grouping, ordering, quantification, aggregation and conversion operators.
• Support for lambda expressions.
• The ability to dynamically define and instantiate anonymous classes.
• Many new “keywords” for Java 1.5 and later.

An example of retrieving a list of product name’s from a list of products is:

List products = Arrays.asList(Product.getAllProducts()); 
Iterable productNames =
 from("p").in(products).
 select("p.getProductName()"); 

Quaere currently has only one implementation (for objects), but a partial implementation is in place for Hibernate. The Hibernate implementation (and others with good criteria APIs) should progress quickly, Anders notes, as the demo of Hibernate only took a few hours.

Several people have noted that joSQL is a similar API. Anders himself notes the similarities but points out some key differences including:

• Quaere has better cohesion with the “business problem”
• Quaere queries are much more compact and have type safety
• Quaere is an extensible language that allows seamless addition of new querying engines

Lastly, Noras has made an attempt to answer common questions about Quaere and has created a project for it on Codehaus.