RelationalExpression.java example

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package org.yamcs.yarch.streamsql;

import org.yamcs.yarch.CompiledExpression;
import org.yamcs.yarch.DataType;
import org.yamcs.yarch.DbReaderStream;
import org.yamcs.yarch.streamsql.StreamSqlException.ErrCode;

import org.yamcs.yarch.streamsql.ColumnExpression;
import org.yamcs.yarch.streamsql.Expression;
import org.yamcs.yarch.streamsql.ParseException;
import org.yamcs.yarch.streamsql.RelOp;
import org.yamcs.yarch.streamsql.StreamSqlException;
import org.yamcs.yarch.streamsql.ValueExpression;
/**
 * Expressions of type "x > y"
 * @author nm
 *
 */
public class RelationalExpression extends Expression {
    RelOp relOp;

    public RelationalExpression(Expression left, Expression right, RelOp relOp) throws ParseException {
        super(new Expression[] {left,right});
        this.relOp=relOp;
        if(left.isConstant() && right.isConstant()) constant=true;
    }


    public RelOp getRelation() {
        return relOp;
    }

    @Override
    public Expression addFilter(DbReaderStream tableStream) throws StreamSqlException {
        if ((children[1] instanceof ColumnExpression) && (children[0].isConstant())) {
            //swap left with right
            Expression tmp=children[1];
            children[1]=children[0];
            children[0]=tmp;
            relOp=relOp.getOppsite();
        }

        if((children[0] instanceof ColumnExpression) && children[1].isConstant()) {
            ColumnExpression cexpr=(ColumnExpression) children[0];
            Object cvalue;
            if(children[1] instanceof ValueExpression) {
                cvalue=((ValueExpression)children[1]).value;
            } else {
                CompiledExpression compexpr=children[1].compile();
                cvalue=compexpr.getValue(null);
            }

            if(tableStream.addRelOpFilter(cexpr,relOp,cvalue))
                return null;
            else 
                return this;
        } else {
            return this;
        }
    }

    @Override
    public void doBind() throws StreamSqlException {
        DataType ltype=children[0].getType();
        DataType rtype=children[1].getType();
        if(!compatibleTypes(ltype,rtype)) throw new StreamSqlException(ErrCode.INCOMPATIBLE, ltype+" and "+rtype);
        type=DataType.BOOLEAN;
    }

    private boolean compatibleTypes(DataType ltype, DataType rtype) {
        // TODO Auto-generated method stub
        return true;
    }

    @Override
    public void fillCode_getValueReturn(StringBuilder code) throws StreamSqlException {
        code.append("(");

        switch(relOp) {
        case NOT_EQUAL:
            code.append("!");
        case EQUAL: //intentional fall through
            children[0].fillCode_getValueReturn(code);
            code.append(".equals(");
            children[1].fillCode_getValueReturn(code);
            code.append(")");
            break;
        default:
            children[0].fillCode_getValueReturn(code);
            code.append(relOp.getSign());
            children[1].fillCode_getValueReturn(code);
        }

        code.append(")");
    }

    @Override
    public String toString() {
        return children[0]+" "+relOp.getSign()+" "+children[1];
    }
}