101: Add support for immutable collection constructor creation

src/main/java/org/apache/ibatis/executor/resultset/PendingConstructorCreation.java

@@ -0,0 +1,146 @@
+/*
+ *    Copyright 2009-2024 the original author or authors.
+ *
+ *    Licensed 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
+ *
+ *       https://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.ibatis.executor.resultset;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+import org.apache.ibatis.executor.ExecutorException;
+import org.apache.ibatis.mapping.ResultMap;
+import org.apache.ibatis.mapping.ResultMapping;
+import org.apache.ibatis.reflection.ReflectionException;
+import org.apache.ibatis.reflection.factory.ObjectFactory;
+
+/**
+ * Represents an object that is still to be created once all nested results with collection values have been gathered
+ *
+ * @author Willie Scholtz
+ */
+final class PendingConstructorCreation {
+
+  private final Class<?> resultType;
+  private final List<Class<?>> constructorArgTypes;
+  private final List<Object> constructorArgs;
+
+  private final Map<Integer, PendingCreationMetaInfo> linkedCollectionMetaInfo;
+  private final Map<PendingCreationKey, Collection<Object>> linkedCollectionsByKey;
+  private final Map<PendingCreationKey, List<PendingConstructorCreation>> linkedCreationsByKey;
+
+  PendingConstructorCreation(Class<?> resultType, List<Class<?>> types, List<Object> args) {
+    // since all our keys are based on result map id, we know we will never go over args size
+    final int maxSize = types.size();
+
+    this.linkedCollectionMetaInfo = new HashMap<>(maxSize);
+    this.linkedCollectionsByKey = new HashMap<>(maxSize);
+    this.linkedCreationsByKey = new HashMap<>(maxSize);
+
+    this.resultType = resultType;
+    this.constructorArgTypes = types;
+    this.constructorArgs = args;
+  }
+
+  @SuppressWarnings("unchecked")
+  Collection<Object> initializeCollectionForResultMapping(ObjectFactory objectFactory, ResultMap resultMap,
+      ResultMapping constructorMapping, Integer index) {
+    final Class<?> parameterType = constructorMapping.getJavaType();
+    if (!objectFactory.isCollection(parameterType)) {
+      throw new ReflectionException(
+          "Cannot add a collection result to non-collection based resultMapping: " + constructorMapping);
+    }
+
+    return linkedCollectionsByKey.computeIfAbsent(new PendingCreationKey(constructorMapping), k -> {
+      // this will allow us to verify the types of the collection before creating the final object
+      linkedCollectionMetaInfo.put(index, new PendingCreationMetaInfo(resultMap.getType(), k));
+
+      // will be checked before we finally create the object) as we cannot reliably do that here
+      return (Collection<Object>) objectFactory.create(parameterType);
+    });
+  }
+
+  void linkCreation(ResultMapping constructorMapping, PendingConstructorCreation pcc) {
+    final PendingCreationKey creationKey = new PendingCreationKey(constructorMapping);
+    final List<PendingConstructorCreation> pendingConstructorCreations = linkedCreationsByKey
+        .computeIfAbsent(creationKey, k -> new ArrayList<>());
+
+    if (pendingConstructorCreations.contains(pcc)) {
+      throw new ExecutorException("Cannot link inner constructor creation with same value, MyBatis internal error!");
+    }
+
+    pendingConstructorCreations.add(pcc);
+  }
+
+  void linkCollectionValue(ResultMapping constructorMapping, Object value) {
+    // not necessary to add null results to the collection
+    if (value == null) {
+      return;
+    }
+
+    linkedCollectionsByKey.computeIfAbsent(new PendingCreationKey(constructorMapping), k -> {
+      throw new ExecutorException("Cannot link collection value for key: " + constructorMapping
+          + ", resultMap has not been seen/initialized yet! Mybatis internal error!");
+    }).add(value);
+  }
+
+  @Override
+  public String toString() {
+    return "PendingConstructorCreation(" + this.hashCode() + "){" + "resultType=" + resultType + '}';
+  }
+
+  /**
+   * Recursively creates the final result of this creation.
+   *
+   * @param objectFactory
+   *          the object factory
+   *
+   * @return the new immutable result
+   */
+  Object create(ObjectFactory objectFactory) {
+    final List<Object> newArguments = new ArrayList<>(constructorArgs.size());
+    for (int i = 0; i < constructorArgs.size(); i++) {
+      final PendingCreationMetaInfo creationMetaInfo = linkedCollectionMetaInfo.get(i);
+      final Object existingArg = constructorArgs.get(i);
+
+      if (creationMetaInfo == null) {
+        // we are not aware of this argument wrt pending creations
+        newArguments.add(existingArg);
+        continue;
+      }
+
+      // time to finally build this collection
+      final PendingCreationKey pendingCreationKey = creationMetaInfo.getPendingCreationKey();
+      final List<PendingConstructorCreation> linkedCreations = linkedCreationsByKey.get(pendingCreationKey);
+      if (linkedCreations != null) {
+        @SuppressWarnings("unchecked")
+        final Collection<Object> emptyCollection = (Collection<Object>) existingArg;
+
+        for (PendingConstructorCreation linkedCreation : linkedCreations) {
+          emptyCollection.add(linkedCreation.create(objectFactory));
+        }
+
+        newArguments.add(emptyCollection);
+        continue;
+      }
+
+      // handle the base collection (it was built inline already)
+      newArguments.add(existingArg);
+    }
+
+    return objectFactory.create(resultType, constructorArgTypes, newArguments);
+  }
+}

src/main/java/org/apache/ibatis/executor/resultset/PendingCreationKey.java

@@ -0,0 +1,67 @@
+/*
+ *    Copyright 2009-2024 the original author or authors.
+ *
+ *    Licensed 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
+ *
+ *       https://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.ibatis.executor.resultset;
+
+import java.util.Objects;
+
+import org.apache.ibatis.mapping.ResultMapping;
+
+/**
+ * A unique identifier for a pending constructor creation, prefix is used to distinguish between equal result maps for
+ * different columns
+ *
+ * @author Willie Scholtz
+ */
+final class PendingCreationKey {
+  private final String resultMapId;
+  private final String constructorColumnPrefix;
+
+  PendingCreationKey(ResultMapping constructorMapping) {
+    this.resultMapId = constructorMapping.getNestedResultMapId();
+    this.constructorColumnPrefix = constructorMapping.getColumnPrefix();
+  }
+
+  String getConstructorColumnPrefix() {
+    return constructorColumnPrefix;
+  }
+
+  String getResultMapId() {
+    return resultMapId;
+  }
+
+  @Override
+  public boolean equals(Object o) {
+    if (this == o)
+      return true;
+    if (o == null || getClass() != o.getClass())
+      return false;
+
+    PendingCreationKey that = (PendingCreationKey) o;
+    return Objects.equals(resultMapId, that.resultMapId)
+        && Objects.equals(constructorColumnPrefix, that.constructorColumnPrefix);
+  }
+
+  @Override
+  public int hashCode() {
+    return Objects.hash(resultMapId, constructorColumnPrefix);
+  }
+
+  @Override
+  public String toString() {
+    return "PendingCreationKey{" + "resultMapId='" + resultMapId + '\'' + ", constructorColumnPrefix='"
+        + constructorColumnPrefix + '\'' + '}';
+  }
+}

src/main/java/org/apache/ibatis/executor/resultset/PendingCreationMetaInfo.java

@@ -0,0 +1,46 @@
+/*
+ *    Copyright 2009-2024 the original author or authors.
+ *
+ *    Licensed 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
+ *
+ *       https://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.ibatis.executor.resultset;
+
+/**
+ * Used to keep track of specific argument types for pending creations
+ *
+ * @author Willie Scholtz
+ */
+final class PendingCreationMetaInfo {
+
+  private final Class<?> argumentType;
+  private final PendingCreationKey pendingCreationKey;
+
+  PendingCreationMetaInfo(Class<?> argumentType, PendingCreationKey pendingCreationKey) {
+    this.argumentType = argumentType;
+    this.pendingCreationKey = pendingCreationKey;
+  }
+
+  Class<?> getArgumentType() {
+    return argumentType;
+  }
+
+  PendingCreationKey getPendingCreationKey() {
+    return pendingCreationKey;
+  }
+
+  @Override
+  public String toString() {
+    return "PendingCreationMetaInfo{" + "argumentType=" + argumentType + ", pendingCreationKey='" + pendingCreationKey
+        + '\'' + '}';
+  }
+}

src/main/java/org/apache/ibatis/mapping/ResultMap.java

@@ -46,6 +46,7 @@ public class ResultMap {
   private Set<String> mappedColumns;
   private Set<String> mappedProperties;
   private Discriminator discriminator;
+  private boolean hasResultMapsUsingConstructorCollection;
   private boolean hasNestedResultMaps;
   private boolean hasNestedQueries;
   private Boolean autoMapping;
@@ -111,6 +112,13 @@ public ResultMap build() {
         }
         if (resultMapping.getFlags().contains(ResultFlag.CONSTRUCTOR)) {
           resultMap.constructorResultMappings.add(resultMapping);
+
+          // #101
+          Class<?> javaType = resultMapping.getJavaType();
+          resultMap.hasResultMapsUsingConstructorCollection = resultMap.hasResultMapsUsingConstructorCollection
+              || (resultMapping.getNestedQueryId() == null && javaType != null
+                  && resultMap.configuration.getObjectFactory().isCollection(javaType));
+
           if (resultMapping.getProperty() != null) {
             constructorArgNames.add(resultMapping.getProperty());
           }
@@ -210,6 +218,10 @@ public String getId() {
     return id;
   }
 
+  public boolean hasResultMapsUsingConstructorCollection() {
+    return hasResultMapsUsingConstructorCollection;
+  }
+
   public boolean hasNestedResultMaps() {
     return hasNestedResultMaps;
   }