ConstantScorePrefixQuery.java

package org.compass.core.lucene.search;

import java.io.IOException;

import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.Term;
import org.apache.lucene.search.ConstantScoreQuery;
import org.apache.lucene.search.PrefixFilter;
import org.apache.lucene.search.Query;

/**
 * A constant score prefix query.
 * 
 * @author kimchy
 */
public class ConstantScorePrefixQuery extends Query {
    private final Term prefix;

    public ConstantScorePrefixQuery(Term prefix) {
        this.prefix = prefix;
    }

    /**
     * Returns the prefix  for this query
     */
    public Term getPrefix() {
        return prefix;
    }

    public Query rewrite(IndexReader reader) throws IOException {
        // TODO: if number of terms are low enough, rewrite to a BooleanQuery
        // for potentially faster execution.
        // TODO: cache the bitset somewhere instead of regenerating it
        Query q = new ConstantScoreQuery(new PrefixFilter(prefix));
        q.setBoost(getBoost());
        return q;
    }

    /**
     * Prints a user-readable version of this query.
     */
    public String toString(String field) {
        StringBuffer buffer = new StringBuffer();
        if (!prefix.field().equals(field)) {
            buffer.append(prefix.field());
            buffer.append(":");
        }
        buffer.append(prefix.text());
        buffer.append('*');
        if (getBoost() != 1.0f) {
            buffer.append("^");
            buffer.append(Float.toString(getBoost()));
        }
        return buffer.toString();
    }

    /**
     * Returns true if <code>o</code> is equal to this.
     */
    public boolean equals(Object o) {
        if (this == o) return true;
        if (!(o instanceof ConstantScorePrefixQuery)) return false;
        ConstantScorePrefixQuery other = (ConstantScorePrefixQuery) o;
        return this.prefix.equals(other.prefix) && this.getBoost() == other.getBoost();
    }

    /**
     * Returns a hash code value for this object.
     */
    public int hashCode() {
        int h = prefix.hashCode() ^ Float.floatToIntBits(getBoost());
        h ^= (h << 14) | (h >>> 19);  // reversible (1 to 1) transformation unique to ConstantScorePrefixQuery
        return h;
    }

}