org.apache.hawq.pxf.api

Class FilterParser

java.lang.Object

org.apache.hawq.pxf.api.FilterParser

public class FilterParser
extends java.lang.Object

The parser code which goes over a filter string and pushes operands onto a stack. Once an operation is read, the evaluate function is called for the FilterParser.FilterBuilder interface with two pop-ed operands.
A string of filters looks like this: a2c5o1a1c"abc"o2o7 which means column#2 < 5 AND column#1 > "abc"
It is a RPN serialized representation of a filters tree in GPDB where

• a means an attribute (column)
• c means a constant (either string or numeric)
• o means operator

Assuming all operators are binary, RPN representation allows it to be read left to right easily.
FilterParser only knows about columns and constants. The rest is up to the FilterParser.FilterBuilder implementer. FilterParser makes sure column objects are always on the left of the expression (when relevant).

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	FilterParser.BasicFilter Basic filter provided for cases where the target storage system does not provide it own filter For example: Hbase storage provides its own filter but for a Writable based record in a SequenceFile there is no filter provided and so we need to have a default
class	FilterParser.ColumnIndex Represents a column index.
class	FilterParser.Constant Represents a constant object (String, Long, ...).
static interface	FilterParser.FilterBuilder Interface a user of FilterParser should implement.
static class	FilterParser.Operation Supported operations by the parser.

Constructor Summary

Constructors

Constructor and Description
FilterParser(FilterParser.FilterBuilder eval) Constructs a FilterParser.

Method Summary

Modifier and Type	Method and Description
java.lang.Object	parse(java.lang.String filter) Parses the string filter.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

FilterParser

public FilterParser(FilterParser.FilterBuilder eval)

Constructs a FilterParser.

Parameters:

eval - the filter builder

Method Detail

parse

public java.lang.Object parse(java.lang.String filter)
                       throws java.lang.Exception

Parses the string filter.

Parameters:

filter - the filter to parse

Returns:

the parsed filter

Throws:

java.lang.Exception - if the filter string had wrong syntax