JsonEachText.java

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package org.apache.doris.nereids.trees.expressions.functions.generator;

import org.apache.doris.catalog.FunctionSignature;
import org.apache.doris.nereids.trees.expressions.Expression;
import org.apache.doris.nereids.trees.expressions.functions.AlwaysNullable;
import org.apache.doris.nereids.trees.expressions.literal.StructLiteral;
import org.apache.doris.nereids.trees.expressions.shape.UnaryExpression;
import org.apache.doris.nereids.trees.expressions.visitor.ExpressionVisitor;
import org.apache.doris.nereids.types.JsonType;
import org.apache.doris.nereids.types.StringType;

import com.google.common.base.Preconditions;
import com.google.common.collect.ImmutableList;

import java.util.List;

/**
 * json_each_text(json) expands the top-level JSON object into a set of
 * key/value pairs.
 * Returns: Struct(key VARCHAR, value VARCHAR) — the JSON value is returned as
 * plain text.
 *
 * Example:
 * SELECT key, value FROM LATERAL VIEW json_each_text('{"a":"foo","b":"bar"}') t
 * AS key, value
 * → key="a", value=foo (plain string, not JSON-quoted)
 * → key="b", value=bar
 */
public class JsonEachText extends TableGeneratingFunction implements UnaryExpression, AlwaysNullable {

    public static final List<FunctionSignature> SIGNATURES = ImmutableList.of(
            FunctionSignature.ret(StructLiteral.constructStructType(
                    ImmutableList.of(StringType.INSTANCE, StringType.INSTANCE)))
                    .args(JsonType.INSTANCE));

    /**
     * Constructor with 1 argument.
     */
    public JsonEachText(Expression arg) {
        super("json_each_text", arg);
    }

    /** Constructor for withChildren and reuse signature. */
    private JsonEachText(GeneratorFunctionParams functionParams) {
        super(functionParams);
    }

    @Override
    public JsonEachText withChildren(List<Expression> children) {
        Preconditions.checkArgument(children.size() == 1);
        return new JsonEachText(getFunctionParams(children));
    }

    @Override
    public List<FunctionSignature> getSignatures() {
        return SIGNATURES;
    }

    @Override
    public <R, C> R accept(ExpressionVisitor<R, C> visitor, C context) {
        return visitor.visitJsonEachText(this, context);
    }
}