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The eobjects.dk MetaModel is a common domain model, query-engine and optimizer for different kinds of datastores.
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/*
 * Copyright 2008 eobjects.dk
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package dk.eobjects.metamodel.query;

import org.apache.commons.lang.builder.EqualsBuilder;

import dk.eobjects.metamodel.schema.Column;
import dk.eobjects.metamodel.schema.Table;
import dk.eobjects.metamodel.schema.Relationship;

/**
 * Represents a FROM item. FROM items can take different forms:
 * 
 * table FROMs (eg. "FROM products p")
 * join FROMs with an ON clause (eg. "FROM products p INNER JOIN orders o ON
 * p.id = o.product_id")
 * 
subquery FROMs (eg. "FROM (SELECT * FROM products) p")
 * 
 * 
 * @see FromClause
 */
public class FromItem implements IQueryItem, Cloneable {

	private static final long serialVersionUID = -6559220014058975193L;
	private Table _table;
	private String _alias;
	private Query _subQuery;
	private JoinType _join;
	private FromItem _leftSide;
	private FromItem _rightSide;
	private SelectItem[] _leftOn;
	private SelectItem[] _rightOn;
	private Query _query;

	/**
	 * Private constructor, used for cloning
	 */
	private FromItem() {
	}

	/**
	 * Constructor for table FROM clauses
	 */
	public FromItem(Table table) {
		_table = table;
	}

	/**
	 * Constructor for sub-query FROM clauses
	 * 
	 * @param subQuery
	 *            the subquery to use
	 */
	public FromItem(Query subQuery) {
		_subQuery = subQuery;
	}

	/**
	 * Constructor for join FROM clauses that join two tables using their
	 * relationship. The primary table of the relationship will be the left side
	 * of the join and the foreign table of the relationship will be the right
	 * side of the join.
	 * 
	 * @param join
	 *            the join type to use
	 * @param relationship
	 *            the relationship to use for joining the tables
	 */
	public FromItem(JoinType join, Relationship relation) {
		_join = join;
		_leftSide = new FromItem(relation.getPrimaryTable());
		Column[] columns = relation.getPrimaryColumns();
		_leftOn = new SelectItem[columns.length];
		for (int i = 0; i < columns.length; i++) {
			_leftOn[i] = new SelectItem(columns[i]);
		}
		_rightSide = new FromItem(relation.getForeignTable());
		columns = relation.getForeignColumns();
		_rightOn = new SelectItem[columns.length];
		for (int i = 0; i < columns.length; i++) {
			_rightOn[i] = new SelectItem(columns[i]);
		}
	}

	/**
	 * Constructor for advanced join types with custom relationships
	 * 
	 * @param join
	 *            the join type to use
	 * @param leftSide
	 *            the left side of the join
	 * @param rightSide
	 *            the right side of the join
	 * @param leftOn
	 *            what left-side select items to use for the ON clause
	 * @param rightOn
	 *            what right-side select items to use for the ON clause
	 */
	public FromItem(JoinType join, FromItem leftSide, FromItem rightSide,
			SelectItem[] leftOn, SelectItem[] rightOn) {
		_join = join;
		_leftSide = leftSide;
		_rightSide = rightSide;
		_leftOn = leftOn;
		_rightOn = rightOn;
	}

	public String getAlias() {
		return _alias;
	}

	public String getSameQueryAlias() {
		if (_alias != null) {
			return _alias;
		}
		if (_table != null) {
			return _table.getQuotedName();
		}
		return null;
	}

	public FromItem setAlias(String alias) {
		_alias = alias;
		return this;
	}

	public Table getTable() {
		return _table;
	}

	public Query getSubQuery() {
		return _subQuery;
	}

	public JoinType getJoin() {
		return _join;
	}

	public FromItem getLeftSide() {
		return _leftSide;
	}

	public FromItem getRightSide() {
		return _rightSide;
	}

	public SelectItem[] getLeftOn() {
		return _leftOn;
	}

	public SelectItem[] getRightOn() {
		return _rightOn;
	}

	@Override
	public String toString() {
		StringBuilder sb = new StringBuilder(toStringNoAlias());
		if (_join != null && _alias != null) {
			sb.insert(0, '(');
			sb.append(')');
		}
		if (_alias != null) {
			sb.append(' ');
			sb.append(_alias);
		}
		return sb.toString();
	}

	public String toStringNoAlias() {
		StringBuilder sb = new StringBuilder();
		if (_table != null) {
			if (_table.getSchema() != null
					&& _table.getSchema().getName() != null) {
				sb.append(_table.getSchema().getName() + '.');
			}
			sb.append(_table.getQuotedName());
		} else if (_subQuery != null) {
			sb.append('(' + _subQuery.toString() + ')');
		} else if (_join != null) {
			String leftSideAlias = _leftSide.getSameQueryAlias();
			String rightSideAlias = _rightSide.getSameQueryAlias();
			sb.append(_leftSide.toString() + ' ' + _join + " JOIN "
					+ _rightSide.toString());
			for (int i = 0; i < _leftOn.length; i++) {
				if (i == 0) {
					sb.append(" ON");
				} else {
					sb.append(" AND ");
				}
				SelectItem primary = _leftOn[i];
				SelectItem foreign = _rightOn[i];
				sb.append(' ');
				if (leftSideAlias != null) {
					sb.append(leftSideAlias + '.');
				}
				sb.append(primary.getSuperQueryAlias());

				sb.append(" = ");
				if (rightSideAlias != null) {
					sb.append(rightSideAlias + '.');
				}
				sb.append(foreign.getSuperQueryAlias());
			}
		}
		return sb.toString();
	}

	/**
	 * Gets the alias of a table, if it is registered (and visible, ie. not part
	 * of a sub-query) in the FromItem
	 * 
	 * @param table
	 *            the table to get the alias for
	 * @return the alias or null if none is found
	 */
	public String getAlias(Table table) {
		String result = null;
		if (table != null) {
			// Search recursively through left and right side, unless they
			// are sub-query FromItems
			if (table.equals(_table)) {
				result = _alias;
			} else if (_join != null) {
				result = _rightSide.getAlias(table);
				if (result == null) {
					result = _leftSide.getAlias(table);
				}
			}
		}
		return result;
	}

	public Query getQuery() {
		return _query;
	}

	public IQueryItem setQuery(Query query) {
		_query = query;
		return this;
	}

	@Override
	protected FromItem clone() {
		FromItem f = new FromItem();
		f._alias = _alias;
		f._join = _join;
		f._table = _table;
		if (_subQuery != null) {
			f._subQuery = _subQuery.clone();
		}
		if (_leftOn != null && _leftSide != null && _rightOn != null
				&& _rightSide != null) {
			f._leftSide = _leftSide.clone();
			f._leftOn = _leftOn.clone();
			f._rightSide = _rightSide.clone();
			f._rightOn = _rightOn.clone();
		}
		return f;
	}

	@Override
	public boolean equals(Object obj) {
		if (obj == this) {
			return true;
		}
		if (obj instanceof FromItem) {
			FromItem that = (FromItem) obj;
			EqualsBuilder eb = new EqualsBuilder();
			eb.append(this.getTable(), that.getTable());
			eb.append(this.getJoin(), that.getJoin());
			eb.append(this.getLeftOn(), that.getLeftOn());
			eb.append(this.getLeftSide(), that.getLeftSide());
			eb.append(this.getRightOn(), that.getRightOn());
			eb.append(this.getRightSide(), that.getRightSide());
			eb.append(this.getSubQuery(), that.getSubQuery());
			eb.append(this.getAlias(), that.getAlias());
			return eb.isEquals();
		}
		return false;
	}
}