Class ScopedSymbol

server/src/main/java/io/crate/expression/symbol/ScopedSymbol.java:53–174

A symbol that associates another symbol with a relation. {@code DocTableRelation | outputs: [Reference(x)] | SELECT t1.x, t2.x FROM tbl AS t1, tbl AS t2 | ~~~~~~~~~

 * </pre>
 */
public final class ScopedSymbol implements Symbol, ScopedColumn {

    private final RelationName relation;
    private final ColumnIdent column;
    private final DataType<?> dataType;

    /**
     * Used to disambiguate columns with the same name.
     **/
    private final int identity;

    /**
     * <p>
     * Creates a ScopedSymbol describing output from a relation.
     * E.g. in the case of UNION its a stand-in for two symbols from the two child
     * relations.
     * </p>
     *
     * Use the {@link #ScopedSymbol(RelationName, ColumnIdent, Symbol)} constructor
     * if the symbol is pointing to a single specific symbol of a child relation
     *
     * @param relation owner of this symbol
     * @param column name of the symbol
     **/
    public ScopedSymbol(RelationName relation, ColumnIdent column, DataType<?> dataType) {
        this.relation = relation;
        this.column = column;
        this.dataType = dataType;
        this.identity = 0;
    }

    /**
     * Creates a ScopedSymbol describing the output from a relation, pointing to a single specific symbol of a child
     * relation.
     * <p>
     * It uses the hashCode of the symbol to disambiguate columns with the same name but different source relations.
     * Using the identity of the symbol is not possible because dynamic or void references are not cached and are
     * created on the fly on every look up. This would lead to different identities for the same symbol.
     * </p>
     *
     * @param relation owner of this symbol
     * @param column name of the symbol
     * @param symbol the symbol this ScopedSymbol is pointing towards
     **/
    public ScopedSymbol(RelationName relation, ColumnIdent column, Symbol symbol) {
        this.relation = relation;
        this.column = column;
        this.dataType = symbol.valueType();
        this.identity = symbol.hashCode();
    }

    public RelationName relation() {
        return relation;
    }

    public ColumnIdent column() {
        return column;
    }