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";

     }

 }