public interface Expression extends QueryElement
Select is usually
an expression together with an alias, a Restriction is
a comparison of two or more expressions, etc.
There are many types of expressions. The simplest ones just insert a
constant value: Expressions.integer(int) or
Expressions.aFloat(float).
Other expressions create a reference to a property or database column:
Hql.property(String, String).
Expressions can also be combined to form other expressions:
Expressions.add(Expression, Expression) or Expressions.divide(Expression, Expression)
Thus it is possible to form a complex tree of expressions:
// The log ratio of foreground intensities: LOG(ch1fg) / LOG(ch2fg)
Expression logRatio = Expressions.divide(
Expressions.log(Hql.property("ch1fg")),
Expressions.log(Hql.property("ch2fg"))
);
The expressions can then be used to create restrictions:
// Return only data with log ratio greater than 2.0 Restrictions.gt(logRatio, Expressions.aFloat(2.0));
The Expressions, Hql, Annotations
and Annotations are factory classes that create expressions.
toQl