WindowFunction<V> class abstract

A window function for sqlite3.

In addition to AggregateFunctions, which run over an entire query, window functions can run over a subset of rows as defined in an OVER clause.

This example defines a window function taking a single argument, which must be an int. The result of the window function is the sum of all arguments in the current window.

class _SumInt implements WindowFunction<int> {
 @override
 AggregateContext<int> createContext() => AggregateContext(0);

 @override
 Object? finalize(AggregateContext<int> context) {
   // There's nothing to finalize, if our [createContext] had side-effects
   // we'd have to undo them here.
   return value(context);
 }

 int _argument(List<Object?> arguments) {
   return arguments.single! as int;
 }

 @override
 void inverse(List<Object?> arguments, AggregateContext<int> context) {
   context.value -= _argument(arguments);
 }

 @override
 void step(List<Object?> arguments, AggregateContext<int> context) {
   context.value += _argument(arguments);
 }

 @override
 Object? value(AggregateContext<int> context) => context.value;
}
Implemented types
Annotations
  • @immutable

Constructors

WindowFunction()

Properties

hashCode → int
The hash code for this object.
no setterinherited
runtimeType → Type
A representation of the runtime type of the object.
no setterinherited

Methods

createContext() → AggregateContext<V>
Creates an initial context holding the initial value before step is called.
inherited
finalize(AggregateContext<V> context) → Object?
Computes the final value from a populated context.
inherited
inverse(List<Object?> arguments, AggregateContext<V> context) → void
Removes the row of arguments from this window.
noSuchMethod(Invocation invocation) → dynamic
Invoked when a nonexistent method or property is accessed.
inherited
step(List<Object?> arguments, AggregateContext<V> context) → void
Adds a new row to the aggregate.
inherited
toString() → String
A string representation of this object.
inherited
value(AggregateContext<V> context) → Object?
Obtain the current aggregate in the window.

Operators

operator ==(Object other) → bool
The equality operator.
inherited