JsonObjectFlatten.java

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

import org.apache.doris.catalog.FunctionSignature;
import org.apache.doris.nereids.trees.expressions.Expression;
import org.apache.doris.nereids.trees.expressions.functions.ExplicitlyCastableSignature;
import org.apache.doris.nereids.trees.expressions.functions.PropagateNullable;
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 com.google.common.base.Preconditions;
import com.google.common.collect.ImmutableList;

import java.util.List;

/**
 * ScalarFunction 'json_object_flatten'. Turn a nested JSONB object into a
 * single-level JSONB object whose keys are dot-joined paths to each leaf
 * (NiFi FlattenJson "keep-arrays" semantics — arrays stay as opaque values):
 *   {"a":{"b":2}}        -> {"a.b":2}
 *   {"a":[{"b":1}]}      -> {"a":[{"b":1}]}
 * To flatten a VARIANT, wrap it with `to_json`: json_object_flatten(to_json(v)).
 */
public class JsonObjectFlatten extends ScalarFunction
        implements UnaryExpression, ExplicitlyCastableSignature, PropagateNullable {

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

    public JsonObjectFlatten(Expression arg0) {
        super("json_object_flatten", arg0);
    }

    private JsonObjectFlatten(ScalarFunctionParams functionParams) {
        super(functionParams);
    }

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

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

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