package liquibase.precondition.core;
   
   import liquibase.changelog.ChangeSet;
   import liquibase.changelog.DatabaseChangeLog;
   import liquibase.database.Database;
   import liquibase.exception.DatabaseException;
   import liquibase.exception.PreconditionErrorException;
   import liquibase.exception.PreconditionFailedException;
   import liquibase.exception.ValidationErrors;
  import liquibase.exception.Warnings;
  import liquibase.precondition.Precondition;
  import liquibase.snapshot.DatabaseSnapshotGeneratorFactory;
  import liquibase.util.StringUtils;
  
  public class ColumnExistsPrecondition implements Precondition {
      private String schemaName;
      private String tableName;
      private String columnName;
  
      public String getSchemaName() {
          return schemaName;
      }
  
      public void setSchemaName(String schemaName) {
          this.schemaName = StringUtils.trimToNull(schemaName);
      }
  
      public String getTableName() {
          return tableName;
      }
  
      public void setTableName(String tableName) {
          this.tableName = tableName;
      }
  
      public String getColumnName() {
          return columnName;
      }
  
      public void setColumnName(String columnName) {
          this.columnName = columnName;
      }
  
      @Override
      public Warnings warn(Database database) {
          return new Warnings();
      }
  
      @Override
      public ValidationErrors validate(Database database) {
          return new ValidationErrors();
      }
  
      @Override
      public void check(Database database, DatabaseChangeLog changeLog, ChangeSet changeSet)
              throws PreconditionFailedException, PreconditionErrorException {
          try {
              if (DatabaseSnapshotGeneratorFactory.getInstance().getGenerator(database)
                      .getColumn(getSchemaName(), getTableName(), getColumnName(), database) == null) {
                  throw new PreconditionFailedException("Column '"
                          + database.escapeColumnName(getSchemaName(), getTableName(), getColumnName())
                          + "' does not exist", changeLog, this);
              }
          } catch (DatabaseException e) {
              throw new PreconditionErrorException(e, changeLog, this);
          }
      }
  
      @Override
      public String getName() {
          return "columnExists";
      }
  }