CoalesceTransformer.java

package com.geni.solr;

import java.sql.SQLException;
import java.util.List;
import java.util.Map;
import java.util.HashMap;
import java.util.Iterator;
import org.apache.solr.handler.dataimport.Context;
import org.apache.solr.handler.dataimport.DataImporter;
import org.apache.solr.handler.dataimport.DataSource;
import com.geni.solr.TemplatedTransformer;

public class CoalesceTransformer extends TemplatedTransformer {

  public Map<String,Object> transformRow(Map<String, Object> row, Context context) {
    List<Map<String,String>> fields = context.getAllEntityFields();

    for (Map<String,String> field : fields) {
      String coalesceTo = field.get("coalesce");

      if (coalesceTo != null) {
        String columnName = field.get(DataImporter.COLUMN);
        String value = (String) row.get(columnName);
        if (value == null) {
          List<String> variables = getVars(coalesceTo);

          if (variables.size() != 1)
            throw new RuntimeException("coalesce value contains more than one templated variable");

          String newValue = (String) context.resolve(variables.get(0));

          if (newValue == null)
            throw new RuntimeException("coalesce templated value unresolvable");

          row.put(columnName, newValue);
        }
      }
    }
    return row;
  }
}

data-config.xml

      <field name="parent_id"
             coalesce="${document.id}"
             column="parent_id"/>