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[CALCITE-3175] AssertionError while serializing to JSON a RexLiteral …
…with Enum type (Wang Yanlin) An example of this is the "LEADING" flag in a call to the "TRIM" function. "LEADING" is an instance of enum SqlTrimFunction.Flag, and becomes a RexLiteral of type SYMBOL. The solution is to serialize enum values as strings, and build a registry of enum classes that may be serialized to JSON and the names of their constants. Since the enums have distinct names (for instance, no other enum class has a constant called "LEADING"), when we deserialize we can use a map to convert them to the correct type. Close apache#1301
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core/src/main/java/org/apache/calcite/rel/externalize/RelEnumTypes.java
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| /* | ||
| * 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.calcite.rel.externalize; | ||
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| import org.apache.calcite.avatica.util.TimeUnitRange; | ||
| import org.apache.calcite.sql.JoinConditionType; | ||
| import org.apache.calcite.sql.JoinType; | ||
| import org.apache.calcite.sql.SqlExplain; | ||
| import org.apache.calcite.sql.SqlExplainFormat; | ||
| import org.apache.calcite.sql.SqlExplainLevel; | ||
| import org.apache.calcite.sql.SqlInsertKeyword; | ||
| import org.apache.calcite.sql.SqlJsonConstructorNullClause; | ||
| import org.apache.calcite.sql.SqlJsonQueryWrapperBehavior; | ||
| import org.apache.calcite.sql.SqlJsonValueEmptyOrErrorBehavior; | ||
| import org.apache.calcite.sql.SqlMatchRecognize; | ||
| import org.apache.calcite.sql.SqlSelectKeyword; | ||
| import org.apache.calcite.sql.fun.SqlTrimFunction; | ||
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| import com.google.common.collect.ImmutableMap; | ||
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| /** Registry of {@link Enum} classes that can be serialized to JSON. | ||
| * | ||
| * <p>Suppose you want to serialize the value | ||
| * {@link SqlTrimFunction.Flag#LEADING} to JSON. | ||
| * First, make sure that {@link SqlTrimFunction.Flag} is registered. | ||
| * The type will be serialized as "SYMBOL". | ||
| * The value will be serialized as the string "LEADING". | ||
| * | ||
| * <p>When we deserialize, we rely on the fact that the registered | ||
| * {@code enum} classes have distinct values. Therefore, knowing that | ||
| * {@code (type="SYMBOL", value="LEADING")} we can convert the string "LEADING" | ||
| * to the enum {@code Flag.LEADING}. */ | ||
| @SuppressWarnings({"rawtypes", "unchecked"}) | ||
| public abstract class RelEnumTypes { | ||
| private RelEnumTypes() {} | ||
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| private static final ImmutableMap<String, Enum<?>> ENUM_BY_NAME; | ||
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| static { | ||
| // Build a mapping from enum constants (e.g. LEADING) to the enum | ||
| // that contains them (e.g. SqlTrimFunction.Flag). If there two | ||
| // enum constants have the same name, the builder will throw. | ||
| final ImmutableMap.Builder<String, Enum<?>> enumByName = | ||
| ImmutableMap.builder(); | ||
| register(enumByName, JoinConditionType.class); | ||
| register(enumByName, JoinType.class); | ||
| register(enumByName, SqlExplain.Depth.class); | ||
| register(enumByName, SqlExplainFormat.class); | ||
| register(enumByName, SqlExplainLevel.class); | ||
| register(enumByName, SqlInsertKeyword.class); | ||
| register(enumByName, SqlJsonConstructorNullClause.class); | ||
| register(enumByName, SqlJsonQueryWrapperBehavior.class); | ||
| register(enumByName, SqlJsonValueEmptyOrErrorBehavior.class); | ||
| register(enumByName, SqlMatchRecognize.AfterOption.class); | ||
| register(enumByName, SqlSelectKeyword.class); | ||
| register(enumByName, SqlTrimFunction.Flag.class); | ||
| register(enumByName, TimeUnitRange.class); | ||
| ENUM_BY_NAME = enumByName.build(); | ||
| } | ||
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| private static void register(ImmutableMap.Builder<String, Enum<?>> builder, | ||
| Class<? extends Enum> aClass) { | ||
| for (Enum enumConstant : aClass.getEnumConstants()) { | ||
| builder.put(enumConstant.name(), enumConstant); | ||
| } | ||
| } | ||
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| /** Converts a literal into a value that can be serialized to JSON. | ||
| * In particular, if is an enum, converts it to its name. */ | ||
| public static Object fromEnum(Object value) { | ||
| return value instanceof Enum ? fromEnum((Enum) value) : value; | ||
| } | ||
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| /** Converts an enum into its name. | ||
| * Throws if the enum's class is not registered. */ | ||
| public static String fromEnum(Enum enumValue) { | ||
| if (ENUM_BY_NAME.get(enumValue.name()) != enumValue) { | ||
| throw new AssertionError("cannot serialize enum value to JSON: " | ||
| + enumValue.getDeclaringClass().getCanonicalName() + "." | ||
| + enumValue); | ||
| } | ||
| return enumValue.name(); | ||
| } | ||
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| /** Converts a string to an enum value. | ||
| * The converse of {@link #fromEnum(Enum)}. */ | ||
| static <E extends Enum<E>> E toEnum(String name) { | ||
| return (E) ENUM_BY_NAME.get(name); | ||
| } | ||
| } | ||
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| // End RelEnumTypes.java |
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