flink-table/flink-table-planner/src/main/java/org/apache/flink/table/planner/expressions/converter/converters/JsonObjectConverter.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.flink.table.planner.expressions.converter.converters;

import org.apache.flink.annotation.Internal;
import org.apache.flink.table.api.JsonOnNull;
import org.apache.flink.table.api.TableException;
import org.apache.flink.table.expressions.CallExpression;
import org.apache.flink.table.expressions.Expression;
import org.apache.flink.table.expressions.ValueLiteralExpression;
import org.apache.flink.table.functions.BuiltInFunctionDefinitions;
import org.apache.flink.table.planner.expressions.converter.CallExpressionConvertRule;
import org.apache.flink.table.planner.functions.sql.FlinkSqlOperatorTable;

import org.apache.calcite.rex.RexNode;
import org.apache.calcite.sql.SqlJsonConstructorNullClause;

import java.util.LinkedList;
import java.util.List;

/** Conversion for {@link BuiltInFunctionDefinitions#JSON_OBJECT}. */
@Internal
class JsonObjectConverter extends CustomizedConverter {
    @Override
    public RexNode convert(CallExpression call, CallExpressionConvertRule.ConvertContext context) {
        checkArgument(call, (call.getChildren().size() - 1) % 2 == 0);
        final List<RexNode> operands = new LinkedList<>();

        final SqlJsonConstructorNullClause onNull =
                ((ValueLiteralExpression) call.getChildren().get(0))
                        .getValueAs(JsonOnNull.class)
                        .map(this::convertOnNull)
                        .orElseThrow(() -> new TableException("Missing argument for ON NULL."));
        operands.add(context.getRelBuilder().getRexBuilder().makeFlag(onNull));

        for (int i = 1; i < call.getChildren().size(); i++) {
            final Expression operand = call.getChildren().get(i);
            if (i % 2 == 1 && !(operand instanceof ValueLiteralExpression)) {
                throw new TableException(
                        String.format("Argument at position %s must be a string literal.", i));
            }

            operands.add(context.toRexNode(operand));
        }

        return context.getRelBuilder()
                .getRexBuilder()
                .makeCall(FlinkSqlOperatorTable.JSON_OBJECT, operands);
    }

    private SqlJsonConstructorNullClause convertOnNull(JsonOnNull onNull) {
        switch (onNull) {
            case NULL:
                return SqlJsonConstructorNullClause.NULL_ON_NULL;
            case ABSENT:
                return SqlJsonConstructorNullClause.ABSENT_ON_NULL;
            default:
                throw new TableException("Unknown ON NULL behavior: " + onNull);
        }
    }
}