org.geotools.expr
Interface Expr

All Known Subinterfaces:

GeometryExpr, MathExpr

All Known Implementing Classes:

org.geotools.expr.AbstractExpr, AbstractGeometryExpr, AbstractMathExpr

public interface Expr

Filter/Expression construction kit - this class forms chains.

I can't take Filter anymore, the turning point was the fact that I needed a FeatureType to make a AttributeExpression. Simply *no*, I cannot expect customer code to have to jump through hoops so that my impmentation is easier. Late binding is required.

The answer - while not completely forcing DataStores away from Expression/Filter is to make a class that captures all the same information and can do the late binding.

On the way we thre we are not going to have the difference between Filter/Expression. Expr can make an Expression, and Expr can make a Filter.

Example:
Exprs.bbox( extent ).and( Exprs.attribute("cost").lt( 50 ) )

BTW: just so we can have everything make sense

• Expr is immutable
• I don't care if Expr trees simplfy themselves during construction
• Allow user to type less by using '.' to mean AND -
  Exprs.bbox( extent ).fids( fidSet) == Exprs.bbox( extent ).and( Exprs.fids( fidSet ) )
• There are convience methods that make sense -
Exprs.bbox( extent ) == geom().disjoint( Expr.literal( extent)).not()
• Or you have to do by hand -
Exprs.fid( "road.1234" ).or( Exprs.fid("road.4321) )

Wild idea time: chaining parameters

• Fid expr above with param chainging?
  Expr.fid( "road.1234" ).param( "road.4321" )
  Of course this idea is really lame given 1.5 new features - kill it :-(
• Of course something like this may be Extactly whtat is needed to make those nasty As FeatureView/Opperation chains work....
  repository.view("road").as("name", "CUSTOMER_NAME").as( "addresss", "ADDRESS" )
  Still does not look right - sigh.

  Author:

  Jody Garnett

  Method Summary

  Expr	and(Expr expr) Explicit Expr chain extention - required for custom Expressions.
  Expr	bbox(com.vividsolutions.jts.geom.Envelope extent) expr.and( geom().bbox().disjoint( extent ).not ) Restrict current Expr with provided bounding box
  Expr	between(Expr min, Expr max) min <= expr <= max
  Expr	eq(Expr expr) expr == expr
  Expr	eval() Evaludate Expr (with LiteralExpr as a goal).
  Expression	expression(FeatureType schema) Lazy binding of Expr into an Expression
  Expr	fid(java.util.Set fids) expr.filter( fids ) Restruct current Expr to provided featureId(s).
  Expr	fid(java.lang.String featureID) expr.filter( fid ) Restruct current Expr to provided featureId(s).
  Filter	filter(FeatureType schema) Lazy binding of Expr into a Filter
  Expr	fn(java.lang.String name) name( expr )
  Expr	fn(java.lang.String name, Expr expr) name( expr, expr )
  Expr	fn(java.lang.String name, Expr[] expr) name( expr[0], expr[0], ... )
  Expr	gt(Expr expr) expr > expr
  Expr	gte(Expr expr) expr >= expr
  Expr	lt(Expr expr) expr < expr
  Expr	lte(Expr expr) expr <= expr
  Expr	ne(Expr expr) expr !
  Expr	not() !
  Expr	notNull() expr !
  Expr	or(Expr expr) Expr Disjunction
  Expr	reduce(java.lang.String bind) Reduce attributes matching "bind/x" to "x".
  Expr	resolve(org.opengis.catalog.MetadataEntity metadata) Bind all meta entries according to provided metadata.
  Expr	resolve(java.lang.String bind, Feature feature) Bind attributes matching "bind/**" to feature.getAttribute("**).

  Method Detail

  eval

  public Expr eval()

  Evaludate Expr (with LiteralExpr as a goal).

  This method has been introduced for testing, although it will help when implementing a testing evaluator.

  Note: The returned result may still be an Expr (if the Expr contains any unresolved metadata or Feature information). If all metadata,geom and attribute Expr have been resolved the result will be a LiteralExpr - that represents the value of the Expr.

  resolve

  public Expr resolve(org.opengis.catalog.MetadataEntity metadata)

  Bind all meta entries according to provided metadata.

  
   Feature
   

  Parameters:

  metadata -

  Returns:

  Expr with all meta( xpath ) Exprs resolved

  reduce

  public Expr reduce(java.lang.String bind)

  Reduce attributes matching "bind/x" to "x".

  This may be used to reduce an Expr as part of an otter join, to something simple that can be passed off to an DataStore by way of filter( FeatureType ).

  Example:

  
   FeatureType RIVER = river.getSchema();
   FeatureType HAZZARD = hazard.getSchema();
   
   Expr joinExpr = Exprs.attribute("river/name").eq( Exprs.attribute("hazzard/river") );
   
   FeatureReader outer = river.getFeatures().reader();
   while( reader.hasNext() ){
     Feature aRiver = outer.next();
   
     Expr inner = joinExpr.resolve( "river", aRiver ).reduce( "hazzard" );
     FeatureReader inner = district.getFeatures( inner.filter( HAZZARD ) );
   	 while( inner.hasNext() ){
        Feature aHazzard = inner.next();
   
   		// code here has access to both aRiver and aHazzard 
     } 
     inner.close();
   }
   outer.close();
   

  resolve

  public Expr resolve(java.lang.String bind,
                      Feature feature)

  Bind attributes matching "bind/**" to feature.getAttribute("**).

  This may be used to reduce an Expr as part of an otter join, to something simple that can be passed off to an DataStore by way of filter( FeatureType ).

  This method will also try and reduce any metadata xpath expression matching "bind/**".

  Parameters:

  bind -

  feature -

  Returns:

  Expr modified with literals in place of "bind/**" attributes.

  filter

  public Filter filter(FeatureType schema)
                throws java.io.IOException

  Lazy binding of Expr into a Filter

  Throws:

  java.io.IOException

  expression

  public Expression expression(FeatureType schema)
                        throws java.io.IOException

  Lazy binding of Expr into an Expression

  Throws:

  java.io.IOException

  bbox

  public Expr bbox(com.vividsolutions.jts.geom.Envelope extent)

  expr.and( geom().bbox().disjoint( extent ).not )

  Restrict current Expr with provided bounding box

  fid

  public Expr fid(java.lang.String featureID)

  expr.filter( fid )

  Restruct current Expr to provided featureId(s).

  fid

  public Expr fid(java.util.Set fids)

  expr.filter( fids )

  Restruct current Expr to provided featureId(s).

  not

  public Expr not()

  !expr

  Invert of logical TRUTH value. Can be used to test for non contained fitler contents or FALSE Expressions

  Returns:

  Invert of Logical TRUETH value

  and

  public Expr and(Expr expr)

  Explicit Expr chain extention - required for custom Expressions.

  Parameters:

  expr -

  Returns:

  Explicit chain extention.

  or

  public Expr or(Expr expr)

  Expr Disjunction

  eq

  public Expr eq(Expr expr)

  expr == expr

  gt

  public Expr gt(Expr expr)

  expr > expr

  gte

  public Expr gte(Expr expr)

  expr >= expr

  lt

  public Expr lt(Expr expr)

  expr < expr

  lte

  public Expr lte(Expr expr)

  expr <= expr

  ne

  public Expr ne(Expr expr)

  expr != expr

  between

  public Expr between(Expr min,
                      Expr max)

  min <= expr <= max

  notNull

  public Expr notNull()

  expr != null

  fn

  public Expr fn(java.lang.String name)

  name( expr )

  fn

  public Expr fn(java.lang.String name,
                 Expr expr)

  name( expr, expr )

  fn

  public Expr fn(java.lang.String name,
                 Expr[] expr)

  name( expr[0], expr[0], ... )