• Introduction
• Installation
• Quick Start
• Design
• DataContext
• Queries
  • SelectQuery
  • Qualifier Expressions
  • Using Orderings
  • SelectQuery Customization
  • Parameterized Queries
  • SQLTemplate Query
  • Scripting SQLTemplate
  • Queries Stored in DataMap
  • Caching Query Results
  • Customizing Queries
  • NamedQuery
  • ObjectIdQuery
  • QueryChain
  • RelationshipQuery
• DataObjects
• Stored Procedures
• Expressions
• Performance Tuning
• Deployment
• Ant Tasks
• Customizing
• DataViews

This chapter is dedicated to the use of expressions as qualifiers. A detailed discussion on expressions in general is provided at Expressions.

The previous chapter showed how to build a query to fetch all data from a single table. In most situations though only a subset of data matching a certain criteria is needed. Cayenne provides an expressions package to control the filtering behavior of the queries. Expressions applied to queries are called "qualifiers".

SelectQuery provides a few ways to initialize and modify the qualifier:

• public SelectQuery(Class objectClass, Expression e)
  Passing expression as a second argument in constructor.
• public void setQualifier(Expression qualifier)
  Explicitly setting the qualifier expression.
• public void andQualifier(Expression e)
  Adding an expression to an already existing qualifier using logical AND.
• public void orQualifier(Expression e)
  Adding an expression to an already existing qualifier using logical OR.