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org.josql.expressions
Class BindVariable  

java.lang.Object
  org.josql.expressions.Expression
      org.josql.expressions.ValueExpression
          org.josql.expressions.BindVariable

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public class BindVariable

extends ValueExpression

This class represents a "bind variable" used within a SQL statement. A bind variable can be either:

• Named - a named bind variable is prefixed with ":", the value of the variable is set in the org.josql.Query object via: Query.setVariable(String,Object)>Query.setVariable(String,Object) 55 . The parser used (javacc generated) is a little picky about "reserved keywords" and as such you cannot use the following as the names of bind variables: select, from, limit, execute, on, all, results, where, having, order, by, group. If you must use one of reserved names then suffix it with "$", i.e. "execute$", "limit$" and so on.
• Anonymous - an anonymous bind variable is represented as "?". The value of the variable is set in the org.josql.Query object via: Query.setVariable(int,Object)>Query.setVariable(int,Object) 55 . Anonymous variables are assigned an internal integer index starting at 1 and they increase by 1.
• Special - there are 3 types of "special" bind variable:
  • :_currobj - Indicates the current object within the execution scope.
  • :_allobjs - Indicates the current set of objects within the execution scope.
  • :_query - Indicates the Query object.
  • :_grpby - Indicates the Group By object. If there are more than 1 group by objects then :_grpby1 ... :_grpby2 ... :_grpbyX can be used to identify which group by object you mean. Remember that the group by object only has meaning if there is a group by statement.
  • :_grpbys - Indicates the set of group bys, this will be a list of lists, one list for each group by key, and each group by column will be in that list.
  • :_groupby - A synonym for :_grpby.
  • :_groupbys - A synonym for :_grpbys.

  Special bind variables are mainly used in function calls however they can also be used just about anywhere.

Examples

   SELECT :_query,
          :_allobjs,
          :_currobj
   FROM java.lang.Object

   SELECT name
   FROM   java.io.File
   WHERE  length(:_currobj, name) > :length
   AND    length > avg(:_query,:_allobjs,length)
   AND    path LIKE '%' + ?
 

Accessors

It is also possible for bind variables (including the special variables) to have accessors. For example:

   SELECT :_query.variables
   FROM   java.lang.Object
 

Would cause all the bind variables in the query to be returned. Also, if the ? in the next query is an instance of java.lang.String.

   SELECT ?.length
   FROM   java.lang.Object
 

Last Modified By: $Author: barrygently $
Last Modified On: $Date: 2004/12/20 16:22:43 $
Current Revision: $Revision: 1.2 $

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Field Summary
private  java.lang.String	acc
private  boolean	anon
private  Getter	get
private  int	groupByInd
private  boolean	groupByVar
private  java.lang.String	name
static java.lang.String	SPECIAL_NAME_PREFIX
private static java.util.Map	SPECIAL_VAR_NAMES
private  java.lang.Object	val

 

Fields inherited from class org.josql.expressions.Expression

 

Constructor Summary

BindVariable()

 

Method Summary
java.lang.Object	evaluate(java.lang.Object o, org.josql.Query q)           Evaluates the value of this bind variable.
java.lang.Class	getExpectedReturnType(org.josql.Query q)           Get the expected return type.
java.lang.String	getName()
java.lang.Object	getValue(java.lang.Object o, org.josql.Query q)           Gets the value of this bind variable.
boolean	hasFixedResult(org.josql.Query q)           Will always return false since a bind variable cannot be fixed.
void	init(org.josql.Query q)           Initialises this bind variable.
private  void	initGetter(java.lang.Class c)
private  void	initGetter(java.lang.Object o)
boolean	isAnonymous()
boolean	isTrue(java.lang.Object o, org.josql.Query q)           Returns whether the value of this bind variable represents a true value.
void	setAccessor(java.lang.String a)
void	setAnonymous(boolean v)
void	setName(java.lang.String name)
java.lang.String	toString()           Returns a string version of this bind variable.

 

Methods inherited from class org.josql.expressions.Expression

isBracketed, setBracketed

 

Methods inherited from class java.lang.Object

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

 

Field Detail

SPECIAL_NAME_PREFIX

public static final java.lang.String SPECIAL_NAME_PREFIX

See Also:

Constant Field Values

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SPECIAL_VAR_NAMES

private static java.util.Map SPECIAL_VAR_NAMES

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name

private java.lang.String name

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val

private java.lang.Object val

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anon

private boolean anon

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acc

private java.lang.String acc

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get

private Getter get

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groupByVar

private boolean groupByVar

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groupByInd

private int groupByInd

Constructor Detail

BindVariable

public BindVariable()

Method Detail

setAccessor

public void setAccessor(java.lang.String a)

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getExpectedReturnType

public java.lang.Class getExpectedReturnType(org.josql.Query q)
                                      throws org.josql.QueryParseException

Get the expected return type. The exact class returned here is dependent (obviously) on what the bind variable represents. Wherever possible it attempts to get the most specific class for the variable. It is generally better to set the variables prior to executing the: Query.parse(String)>Query.parse(String) 55 method to ensure that the correct class is returned here.

Specified by:

getExpectedReturnType in class Expression

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init

public void init(org.josql.Query q)
          throws org.josql.QueryParseException

Initialises this bind variable. If the bind variable is "anonymous" then a name is gained for it from the Query object. If there is a value then it is gained from the Query object and cached. Also, if there is an accessor defined then it is inited where possible.

Specified by:

init in class Expression

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getName

public java.lang.String getName()

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isAnonymous

public boolean isAnonymous()

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setAnonymous

public void setAnonymous(boolean v)

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setName

public void setName(java.lang.String name)

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initGetter

private void initGetter(java.lang.Object o)

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initGetter

private void initGetter(java.lang.Class c)

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getValue

public java.lang.Object getValue(java.lang.Object o,
                                 org.josql.Query q)
                          throws org.josql.QueryExecutionException

Gets the value of this bind variable.

Overrides:

getValue in class ValueExpression

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isTrue

public boolean isTrue(java.lang.Object o,
                      org.josql.Query q)
               throws org.josql.QueryExecutionException

Returns whether the value of this bind variable represents a true value. See: ArithmeticExpression.isTrue(Object,Query) 55 for details of how the return value is determined.

Specified by:

isTrue in class Expression

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evaluate

public java.lang.Object evaluate(java.lang.Object o,
                                 org.josql.Query q)
                          throws org.josql.QueryExecutionException

Evaluates the value of this bind variable. This is just a thin-wrapper around: getValue(Object,Query) 55 .

Specified by:

evaluate in class ValueExpression

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toString

public java.lang.String toString()

Returns a string version of this bind variable. Returns in the form: ? | ":" [ "_" ] Name

Specified by:

toString in class Expression

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hasFixedResult

public boolean hasFixedResult(org.josql.Query q)

Will always return false since a bind variable cannot be fixed.

Specified by:

hasFixedResult in class Expression

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