JsonEach.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(json) expands the top-level JSON object into a set of key/value
 * pairs.
 * Returns: Struct(key VARCHAR, value JSON) — one row per top-level key.
 *
 * Example:
 * SELECT key, value FROM LATERAL VIEW json_each('{"a":"foo","b":"bar"}') t AS
 * key, value
 * → key="a", value="foo" (JSON-formatted)
 * → key="b", value="bar"
 */
public class JsonEach extends TableGeneratingFunction implements UnaryExpression, AlwaysNullable {

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

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

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

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

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

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