refs #364 Throws exception when collection type is ambiguous.

src/main/java/org/apache/ibatis/builder/xml/XMLMapperBuilder.java

@@ -405,13 +405,26 @@ private String processNestedResultMappings(XNode context, List<ResultMapping> re
         || "collection".equals(context.getName())
         || "case".equals(context.getName())) {
       if (context.getStringAttribute("select") == null) {
+        validateCollection(context, enclosingType);
         ResultMap resultMap = resultMapElement(context, resultMappings, enclosingType);
         return resultMap.getId();
       }
     }
     return null;
   }
 
+  protected void validateCollection(XNode context, Class<?> enclosingType) {
+    if ("collection".equals(context.getName()) && context.getStringAttribute("resultMap") == null
+      && context.getStringAttribute("resultType") == null) {
+      MetaClass metaResultType = MetaClass.forClass(enclosingType, configuration.getReflectorFactory());
+      String property = context.getStringAttribute("property");
+      if (!metaResultType.hasSetter(property)) {
+        throw new BuilderException(
+          "Ambiguous collection type for property '" + property + "'. You must specify 'resultType' or 'resultMap'.");
+      }
+    }
+  }
+
   private void bindMapperForNamespace() {
     String namespace = builderAssistant.getCurrentNamespace();
     if (namespace != null) {

src/test/java/org/apache/ibatis/submitted/stringlist/MapperInvalid.xml

@@ -0,0 +1,34 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+
+       Copyright 2009-2018 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
+
+          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.
+
+-->
+<!DOCTYPE mapper
+    PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
+    "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
+
+<mapper
+  namespace="org.apache.ibatis.submitted.stringlist.MapperInvalid">
+
+  <resultMap type="map" id="invalidResultMap">
+    <id column="id" property="id" />
+    <!-- collection type is not resolvable -->
+    <collection property="groups" ofType="string">
+      <result column="group_id" />
+    </collection>
+  </resultMap>
+
+</mapper>

src/test/java/org/apache/ibatis/submitted/stringlist/StringListTest.java

@@ -15,10 +15,13 @@
  */
 package org.apache.ibatis.submitted.stringlist;
 
+import static org.junit.Assert.*;
+
 import java.io.Reader;
 import java.util.List;
 
 import org.apache.ibatis.BaseDataTest;
+import org.apache.ibatis.exceptions.PersistenceException;
 import org.apache.ibatis.io.Resources;
 import org.apache.ibatis.session.SqlSession;
 import org.apache.ibatis.session.SqlSessionFactory;
@@ -40,7 +43,7 @@ public static void setUp() throws Exception {
 
     // populate in-memory database
     BaseDataTest.runScript(sqlSessionFactory.getConfiguration().getEnvironment().getDataSource(),
-            "org/apache/ibatis/submitted/stringlist/CreateDB.sql");
+      "org/apache/ibatis/submitted/stringlist/CreateDB.sql");
   }
 
   @Test
@@ -54,4 +57,15 @@ public void shouldGetAUser() {
     }
   }
 
+  @Test
+  public void shouldFailFastIfCollectionTypeIsAmbiguous() throws Exception {
+    try (Reader reader = Resources
+      .getResourceAsReader("org/apache/ibatis/submitted/stringlist/mybatis-config-invalid.xml")) {
+      new SqlSessionFactoryBuilder().build(reader);
+      fail("Should throw exception when collection type is unresolvable.");
+    } catch (PersistenceException e) {
+      assertTrue(e.getMessage()
+        .contains("Ambiguous collection type for property 'groups'. You must specify 'resultType' or 'resultMap'."));
+    }
+  }
 }

src/test/java/org/apache/ibatis/submitted/stringlist/mybatis-config-invalid.xml

@@ -0,0 +1,42 @@
+<?xml version="1.0" encoding="UTF-8" ?>
+<!--
+
+       Copyright 2009-2018 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
+
+          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.
+
+-->
+<!DOCTYPE configuration
+    PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
+    "http://mybatis.org/dtd/mybatis-3-config.dtd">
+
+<configuration>
+
+	<environments default="development">
+		<environment id="development">
+			<transactionManager type="JDBC">
+				<property name="" value="" />
+			</transactionManager>
+			<dataSource type="UNPOOLED">
+				<property name="driver" value="org.hsqldb.jdbcDriver" />
+				<property name="url" value="jdbc:hsqldb:mem:stringlistinvalid" />
+				<property name="username" value="sa" />
+			</dataSource>
+		</environment>
+	</environments>
+
+	<mappers>
+		<mapper resource="org/apache/ibatis/submitted/stringlist/MapperInvalid.xml" />
+	</mappers>
+
+</configuration>