NormalizeElementAt.java

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package org.apache.doris.nereids.rules.expression.rules;

import org.apache.doris.nereids.rules.expression.ExpressionPatternMatcher;
import org.apache.doris.nereids.rules.expression.ExpressionPatternRuleFactory;
import org.apache.doris.nereids.rules.expression.ExpressionRuleType;
import org.apache.doris.nereids.trees.expressions.Expression;
import org.apache.doris.nereids.trees.expressions.functions.scalar.ElementAt;
import org.apache.doris.nereids.trees.expressions.literal.IntegerLikeLiteral;
import org.apache.doris.nereids.trees.expressions.literal.StringLiteral;
import org.apache.doris.nereids.types.StructField;
import org.apache.doris.nereids.types.StructType;

import com.google.common.collect.ImmutableList;

import java.util.List;

/**
 * given column s has data type: struct<a: int, b: int>, if exists element_at(s, 2), we will rewrite
 * to element_at(s, 'b'). Only applies to element_at over a struct; array/map keep their int index.
 */
public class NormalizeElementAt implements ExpressionPatternRuleFactory {
    public static final NormalizeElementAt INSTANCE = new NormalizeElementAt();

    @Override
    public List<ExpressionPatternMatcher<? extends Expression>> buildRules() {
        return ImmutableList.of(
                matchesType(ElementAt.class).then(NormalizeElementAt::normalize)
                        .toRule(ExpressionRuleType.NORMALIZE_ELEMENT_AT)
        );
    }

    private static Expression normalize(ElementAt elementAt) {
        if (!(elementAt.child(0).getDataType() instanceof StructType)) {
            return elementAt;
        }
        Expression field = elementAt.getArgument(1);
        if (field instanceof IntegerLikeLiteral) {
            int fieldIndex = ((Number) ((IntegerLikeLiteral) field).getValue()).intValue();
            StructType structType = (StructType) elementAt.child(0).getDataType();
            List<StructField> fields = structType.getFields();
            if (fieldIndex >= 1 && fieldIndex <= fields.size()) {
                return elementAt.withChildren(
                        ImmutableList.of(
                                elementAt.child(0),
                                new StringLiteral(fields.get(fieldIndex - 1).getName())
                        )
                );
            }
        }
        return elementAt;
    }
}