com.h3c.util.persistence.cassandra.entitymgr.column

Class CustomColumn<C extends Serializable & Comparable<C>,D>

java.lang.Object

com.h3c.util.persistence.cassandra.entitymgr.column.Column<C,D>

com.h3c.util.persistence.cassandra.entitymgr.column.CustomColumn<C,D>

Type Parameters:

C - type of the column name or column key

D - type of the column value

All Implemented Interfaces:

Visitable<ColumnVisitor<C>>

public class CustomColumn<C extends Serializable & Comparable<C>,D>
extends Column<C,D>

Custom column.

A custom column is normally used to create a composite column which is normally used to implement filtering with a secondary index. For example, to filter persons by Status and Sex ("Get all female single persons") a composite column that stores the status and sex can be created and a secondary index can be set. Thus the column family to store persons would have a column for status ( to support filtering by status), a column for sex (to support filtering by sex) and a composite column for status-sex.

A composite column is also used to implement super columns. Astyanax deprecated ColumnPath with the following comment: "Super columns should be replaced with composite columns". All super columns support was dropped in favor of composite columns. Cassandra will eventually replace the super column implementation with composite columns.

Note that composite columns that will act as super columns are nornally not indexed since they will tend to store several values.

Note: In order to use the value of a custom column, when it is read from the column family, it will have to be casted.

 Column<C, ?> column = read(...);
 SomeObj someObj =  (SomeObj)column.getValue();
 

For specific applications that use specific custom values an additional visitor pattern may be used to avoid casting. For each subclass of CustomColumn a ColumnDecoder will have to be created too to create the right subclass instance. However the same CustomColumn.CustomIndexValueExpressionStrategy can be used.

Example:

 public abstract class MyCustomColumn<C extends Serializable & 
         Comparable<C>, D> extends CustomColumn<C, D> {
     ...
     public abstract void accept(MyCustomColumnVisitor<C> visitor); 
 }
 
 public class SomeObjColumn<C extends Serializable & Comparable<C>
 >extends MyCustomColumn<C, SomeObj> {
     ...
     @Override
     public void accept(MyCustomColumnVisitor<C> visitor) {
         visitor.visit(this);
     } 
 }
 
 public interface MyCustomColumnVisitor<C extends Serializable & 
         Comparable<C>> {
     public void visit(SomeObjColumn<C> column);
 }
 

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	CustomColumn.CustomColumnDecoder<C extends Serializable & Comparable<C>,D> Custom column decoder.
static class	CustomColumn.CustomIndexValueExpressionStrategy<K extends Serializable,C extends Serializable & Comparable<C>,D> Custom index value expression strategy.

Field Summary

Fields inherited from class com.h3c.util.persistence.cassandra.entitymgr.column.Column

serializer

Constructor Summary

Constructors

Constructor and Description
CustomColumn(ColumnName<C,D> name) Creates a boolean column with no value
CustomColumn(ColumnName<C,D> name, D value, com.netflix.astyanax.Serializer<D> serializer) Creates a boolean column.

Method Summary

Methods

Modifier and Type	Method and Description
void	accept(ColumnVisitor<C> visitor) Calls a visit method of the visitor, this class object passes itself as an argument to the visit method this class object.
void	addToMutation(com.netflix.astyanax.ColumnListMutation<C> mutation) Adds the column to a mutation.
com.netflix.astyanax.Execution<Void>	addToMutation(com.netflix.astyanax.ColumnMutation mutation) Adds the column to a mutation.
int	compareTo(Column<C,D> o2)

Methods inherited from class com.h3c.util.persistence.cassandra.entitymgr.column.Column

equals, getName, getSerializer, getValue, hashCode, toString

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Constructor Detail

CustomColumn

public CustomColumn(ColumnName<C,D> name)

Creates a boolean column with no value

Parameters:

name - column's name

CustomColumn

public CustomColumn(ColumnName<C,D> name,
            D value,
            com.netflix.astyanax.Serializer<D> serializer)

Creates a boolean column.

Parameters:

name - column's name

value - column's value

serializer - serializer

Method Detail

compareTo

public int compareTo(Column<C,D> o2)

Specified by:

compareTo in class Column<C extends Serializable & Comparable<C>,D>

accept

public void accept(ColumnVisitor<C> visitor)

Calls a visit method of the visitor, this class object passes itself as an argument to the visit method this class object.

Parameters:

visitor - ColumnVisitor

addToMutation

public com.netflix.astyanax.Execution<Void> addToMutation(com.netflix.astyanax.ColumnMutation mutation)

Adds the column to a mutation.

Parameters:

mutation - to add the column to

Returns:

execution

addToMutation

public void addToMutation(com.netflix.astyanax.ColumnListMutation<C> mutation)

Adds the column to a mutation.

Parameters:

mutation - to add the column to