org.apache.openjpa.jdbc.kernel.exps
Class GetColumn

java.lang.Object
  org.apache.openjpa.jdbc.kernel.exps.GetColumn

All Implemented Interfaces:

Serializable, JDBCFilterListener, FilterListener

public class GetColumn
extends Object
implements JDBCFilterListener

Returns the SQL alias of the named column for use in a query. Note that to retrieve columns in the table of the candidate object, you must explicitly qualify the extension with this, as demonstrated in the second example below. Examples:
"company.address.ext:getColumn (\"ID\") == 5"
"this.ext:getColumn (\"CLS\") == \"org.apache.openjpa.example.Person\""

See Also:

Serialized Form

Field Summary

static String

TAG

Constructor Summary

GetColumn()

Method Summary

void	appendTo(SQLBuffer buf, FilterValue target, FilterValue[] args, ClassMapping type, JDBCStore store) Append the SQL for this expression or value.
Object	evaluate(Object target, Class targetClass, Object[] args, Class[] argClasses, Object candidate, StoreContext ctx) Evaluate the given expression.
boolean	expectsArguments() Return true if this extension expects arguments to act on.
boolean	expectsTarget() Return true if this extension expects a target to act on.
String	getTag() Return the tag that this extension listens for.
Class	getType(Class targetClass, Class[] argClasses) Return the expected type of the result of this listener.

Methods inherited from class java.lang.Object

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

Field Detail

TAG

public static final String TAG

See Also:

Constant Field Values

Constructor Detail

GetColumn

public GetColumn()

Method Detail

getTag

public String getTag()

Description copied from interface: FilterListener

Return the tag that this extension listens for.

Specified by:

getTag in interface FilterListener

expectsArguments

public boolean expectsArguments()

Description copied from interface: FilterListener

Return true if this extension expects arguments to act on. Some extensions may not need arguments; for example, an extension to switch a string to upper case might be of the form: field.ext:toUpperCase ().

Specified by:

expectsArguments in interface FilterListener

expectsTarget

public boolean expectsTarget()

Description copied from interface: FilterListener

Return true if this extension expects a target to act on. Some extensions act on a field or object value; others stand alone. field.ext:toUpperCase () acts on the target field but has no arguments, while another possible form, ext:toUpperCase (field) has no target but does have an argument.

Specified by:

expectsTarget in interface FilterListener

evaluate

public Object evaluate(Object target,
                       Class targetClass,
                       Object[] args,
                       Class[] argClasses,
                       Object candidate,
                       StoreContext ctx)

Description copied from interface: FilterListener

Evaluate the given expression. This method is used when evaluating in-memory expressions. The method used when evaluating data store expressions will change depending on the data store in use.

Specified by:

evaluate in interface FilterListener

Parameters:

target - the target object / field value to act on; will be null if this extension does not expect a target

targetClass - the expected class of the target; given in case the target evaluates to null and typing is needed

args - the values of the arguments given in the filter; will be null if this extension does not expect an argument

argClasses - the expected classes of the arguments; given in case an argument evaluates to null and typing is needed

candidate - the candidate object being evaluated

ctx - the persistence context

Returns:

the value of the extension for this candidate; if this extension is an expression, this method should return Boolean.TRUE or Boolean.FALSE

appendTo

public void appendTo(SQLBuffer buf,
                     FilterValue target,
                     FilterValue[] args,
                     ClassMapping type,
                     JDBCStore store)

Description copied from interface: JDBCFilterListener

Append the SQL for this expression or value.

Specified by:

appendTo in interface JDBCFilterListener

Parameters:

buf - the SQL buffer to append to

target - the target to act on, or null if the listener doesn't expect a target

args - the values of the arguments given in the filter, or null if this listener doesn't expect arguments

type - the class mapping for the query's candidate class

store - the store that owns the query

getType

public Class getType(Class targetClass,
                     Class[] argClasses)

Description copied from interface: FilterListener

Return the expected type of the result of this listener.

Specified by:

getType in interface FilterListener

Parameters:

targetClass - the expected class of the target, or null if no target

argClasses - the expected classes of the arguments, or null if no arguments