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Hibernate version:
3.1


The following is comming from projections class header

/**
* The <tt>criterion</tt> package may be used by applications as a framework for building
* new kinds of <tt>Projection</tt>. However, it is intended that most applications will
* simply use the built-in projection types via the static factory methods of this class.<br/>
* <br/>
* The factory methods that take an alias allow the projected value to be referred to by
* criterion and order instances.

Dose that mean we can write our own peojections like stddev, to_char, trunc especially to use with oracle. Another developer from my team suggested that this is not a good practice referring back to the paragraph listed above.

What I am doing is basically extending SimpleProjection for a TruncProjection and AggregateProjection for a StddevProjection and other projections mainly extending SimpleProjection and AggregateProjection.

Can someone from the hibernate team please advise. Personally I think that there is a need to implement such projections and doing that should not be a problem. Am I wrong?

Thank You for your advise.


Please see below the code for the classes, this is a first effort its not finalized. Any suggestion/advise is realy appreciated.


*********************************
import org.hibernate.criterion.AggregateProjection;
public class ExtendedProjections {

private ExtendedProjections() {
}

public static StdProjection stddev(String propertyName) {
return new StdProjection(propertyName);
}

public static TruncProjection trunc(String propertyName, String format) {
return new TruncProjection(propertyName, format);
}
public static ToCharProjection toChar(String propertyName, String format) {
return new ToCharProjection(propertyName, format);
}
public static ToCharProjection toChar(AggregateProjection projection, String format) {
return new ToCharProjection(projection, format);
}
}



***************************************

mport org.hibernate.Criteria;
import org.hibernate.HibernateException;
import org.hibernate.criterion.AggregateProjection;
import org.hibernate.criterion.CriteriaQuery;
import org.hibernate.criterion.SimpleProjection;
import org.hibernate.type.Type;
import org.hibernate.util.StringHelper;

public class ToCharProjection extends SimpleProjection {
private final String aggregate;
protected String propertyName;
private String format;
private AggregateProjection projection;

public ToCharProjection(String propertyName, String format) {
this("to_char", propertyName, null, format);
}

public ToCharProjection(AggregateProjection projection, String format) {
this("to_char", null, projection, format);
}
public ToCharProjection(String aggregate, String propertyName,
AggregateProjection projection, String format) {
this.aggregate=aggregate;
this.propertyName = propertyName;
this.format = format;
this.projection = projection;
}

public String toString() {
if(propertyName!=null && !propertyName.equals(""))
return aggregate+"(" + propertyName + ","+ format+ ')';
else
return aggregate+"(" + projection.toString() + ","+ format+ ')';
}

public Type[] getTypes(Criteria criteria, CriteriaQuery criteriaQuery)
throws HibernateException {
return projection.getTypes(criteria, criteriaQuery);
//return new Type[] { criteriaQuery.getType(criteria, propertyName) };
}

public String toSqlString(Criteria criteria, int loc, CriteriaQuery criteriaQuery)
throws HibernateException {
StringBuffer buffer = new StringBuffer()
.append(aggregate)
.append("(");
if(propertyName!=null && !propertyName.equals(""))
buffer.append( criteriaQuery.getColumn(criteria, propertyName) );
else if(projection!=null){
buffer.append(projection.toString());
}
else
;//TODO:
buffer.append( ", '"+format+"'" ).append(") as y")
.append(loc)
.append('_');
return buffer.toString();
}

}

**********************************


public class TruncProjection extends SimpleProjection {
protected final String propertyName;
private final String aggregate;
private final String format;

public TruncProjection(String propertyName, String format) {
this.aggregate = "trunc";
this.propertyName = propertyName;
this.format = format;
}

public String toString() {
return aggregate + "(" + propertyName + ","+ format+ ')';
}

public Type[] getTypes(Criteria criteria, CriteriaQuery criteriaQuery)
throws HibernateException {
return new Type[] { criteriaQuery.getType(criteria, propertyName) };
}

public String toSqlString(Criteria criteria, int loc, CriteriaQuery criteriaQuery)
throws HibernateException {
StringBuffer buffer = new StringBuffer()
.append(aggregate)
.append("(")
.append( criteriaQuery.getColumn(criteria, propertyName) )
.append( ", '"+format+"'" ).append(") as y")
.append(loc)
.append('_');
return buffer.toString();
}

public boolean isGrouped() {
return true;
}
/*
public String toGroupSqlString(Criteria criteria, CriteriaQuery criteriaQuery)
throws HibernateException {
throw new UnsupportedOperationException("not a grouping projection");
}*/
public String toGroupSqlString(Criteria criteria, CriteriaQuery criteriaQuery)
throws HibernateException {
return StringHelper.replace( aggregate+"("+criteriaQuery.getColumn(criteria, propertyName)+", '"+format+"')", "{alias}", criteriaQuery.getSQLAlias(criteria) );
}
}


*******************************************************


public class StdProjection extends AggregateProjection {
public StdProjection(String propertyName) {
super("stddev", propertyName);
}
public Type[] getTypes(Criteria criteria, CriteriaQuery criteriaQuery)
throws HibernateException {
return new Type[] { Hibernate.DOUBLE };
}
}