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   *  to you under the Apache License, Version 2.0 (the
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  package org.apache.cayenne.dbsync.merge.factory;
  
  import org.apache.cayenne.dba.DbAdapter;
  import org.apache.cayenne.dba.QuotingStrategy;
  import org.apache.cayenne.dbsync.merge.token.MergerToken;
  import org.apache.cayenne.dbsync.merge.token.db.AddColumnToDb;
  import org.apache.cayenne.dbsync.merge.token.db.DropColumnToDb;
  import org.apache.cayenne.dbsync.merge.token.db.SetAllowNullToDb;
  import org.apache.cayenne.dbsync.merge.token.db.SetNotNullToDb;
  import org.apache.cayenne.map.DbAttribute;
  import org.apache.cayenne.map.DbEntity;
  
  import java.util.Collections;
  import java.util.List;
  
  public class FirebirdMergerTokenFactory extends DefaultMergerTokenFactory {
  
      @Override
      public MergerToken createDropColumnToDb(DbEntity entity, DbAttribute column) {
          return new DropColumnToDb(entity, column) {
              public List<String> createSql(DbAdapter adapter) {
                  QuotingStrategy quoting = adapter.getQuotingStrategy();
                  return Collections.singletonList("ALTER TABLE " + quoting.quotedFullyQualifiedName(getEntity())
                          + " DROP " + quoting.quotedName(getColumn()));
              }
          };
      }
      
      @Override
      public MergerToken createSetNotNullToDb(DbEntity entity, DbAttribute column) {
          return new SetNotNullToDb(entity, column) {
              public List<String> createSql(DbAdapter adapter) {
                  QuotingStrategy context = adapter.getQuotingStrategy();
                  String entityName = context.quotedFullyQualifiedName(getEntity()) ;
                  String columnName = context.quotedName(getColumn());
                  // Firebird doesn't support ALTER TABLE table_name ALTER column_name SET NOT NULL
                  // but this might be achived by modyfication of system tables 
                  return Collections.singletonList(String.format("UPDATE RDB$RELATION_FIELDS SET RDB$NULL_FLAG = 1 "+ 
                  "WHERE RDB$FIELD_NAME = '%s' AND RDB$RELATION_NAME = '%s'", columnName, entityName));
              }
          };
      }
      
      @Override
      public MergerToken createSetAllowNullToDb(DbEntity entity, DbAttribute column) {
          return new SetAllowNullToDb(entity, column) {
              public List<String> createSql(DbAdapter adapter) {
                  QuotingStrategy context = adapter.getQuotingStrategy();
                  String entityName = context.quotedFullyQualifiedName(getEntity()) ;
                  String columnName = context.quotedName(getColumn()); 
                  // Firebird doesn't support ALTER TABLE table_name ALTER column_name DROP NOT NULL
                  // but this might be achived by modyfication system tables 
                  return Collections.singletonList(String.format("UPDATE RDB$RELATION_FIELDS SET RDB$NULL_FLAG = NULL "+
                  " WHERE RDB$FIELD_NAME = '%s' AND RDB$RELATION_NAME = '%s'", columnName, entityName));
              }
          };
      }
  
      @Override
      public MergerToken createAddColumnToDb(DbEntity entity, DbAttribute column) {
          return new AddColumnToDb(entity, column) {
              protected void appendPrefix(StringBuffer sqlBuffer, QuotingStrategy context) {
                  sqlBuffer.append("ALTER TABLE ");
                  sqlBuffer.append(context.quotedFullyQualifiedName(getEntity()));
                  sqlBuffer.append(" ADD ");
                  sqlBuffer.append(context.quotedName(getColumn()));
                  sqlBuffer.append(" ");
              }
          };
      }
  
  }
  