From 7e09c8a647972fe576be613d0df527936fd86549 Mon Sep 17 00:00:00 2001
From: JiHongYuan <1206429202@qq.com>
Date: Wed, 13 Oct 2021 00:50:48 +0800
Subject: [PATCH 1/4] fix discriminator use resultMap not type, use constructor
 NullPointerException

---
 src/main/java/org/apache/ibatis/mapping/ResultMap.java | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/main/java/org/apache/ibatis/mapping/ResultMap.java b/src/main/java/org/apache/ibatis/mapping/ResultMap.java
index 48071c204b6..92e9a3ac088 100644
--- a/src/main/java/org/apache/ibatis/mapping/ResultMap.java
+++ b/src/main/java/org/apache/ibatis/mapping/ResultMap.java
@@ -122,7 +122,7 @@ public ResultMap build() {
       if (resultMap.idResultMappings.isEmpty()) {
         resultMap.idResultMappings.addAll(resultMap.resultMappings);
       }
-      if (!constructorArgNames.isEmpty()) {
+      if (!constructorArgNames.isEmpty() && resultMap.type != null) {
         final List<String> actualArgNames = argNamesOfMatchingConstructor(constructorArgNames);
         if (actualArgNames == null) {
           throw new BuilderException("Error in result map '" + resultMap.id

From 748d296a57c63af21de9cf2d2dafa6c4a8416098 Mon Sep 17 00:00:00 2001
From: JiHongYuan <1206429202@qq.com>
Date: Wed, 13 Oct 2021 00:51:37 +0800
Subject: [PATCH 2/4] Update Test Cased

---
 src/test/java/org/apache/ibatis/builder/xsd/BlogMapper.xml | 3 +++
 src/test/java/org/apache/ibatis/domain/blog/DraftPost.java | 6 ++++++
 src/test/java/org/apache/ibatis/domain/blog/Post.java      | 7 +++++++
 3 files changed, 16 insertions(+)

diff --git a/src/test/java/org/apache/ibatis/builder/xsd/BlogMapper.xml b/src/test/java/org/apache/ibatis/builder/xsd/BlogMapper.xml
index d01680da2e7..255a03536ea 100644
--- a/src/test/java/org/apache/ibatis/builder/xsd/BlogMapper.xml
+++ b/src/test/java/org/apache/ibatis/builder/xsd/BlogMapper.xml
@@ -83,6 +83,9 @@
   </resultMap>
 
   <resultMap id="joinedPost" type="org.apache.ibatis.domain.blog.Post">
+    <constructor>
+      <idArg column="post_id" name="id"/>
+    </constructor>
     <id property="id" column="post_id"/>
     <result property="subject" column="post_subject"/>
     <association property="author" resultMap="joinedAuthor"/>
diff --git a/src/test/java/org/apache/ibatis/domain/blog/DraftPost.java b/src/test/java/org/apache/ibatis/domain/blog/DraftPost.java
index 0ab0d7167bf..fc30d70f773 100644
--- a/src/test/java/org/apache/ibatis/domain/blog/DraftPost.java
+++ b/src/test/java/org/apache/ibatis/domain/blog/DraftPost.java
@@ -16,4 +16,10 @@
 package org.apache.ibatis.domain.blog;
 
 public class DraftPost extends Post {
+  public DraftPost() {
+  }
+
+  public DraftPost(int id) {
+    super(id);
+  }
 }
diff --git a/src/test/java/org/apache/ibatis/domain/blog/Post.java b/src/test/java/org/apache/ibatis/domain/blog/Post.java
index 345b43c01b6..d82238a56f6 100644
--- a/src/test/java/org/apache/ibatis/domain/blog/Post.java
+++ b/src/test/java/org/apache/ibatis/domain/blog/Post.java
@@ -30,6 +30,13 @@ public class Post {
   private List<Comment> comments;
   private List<Tag> tags;
 
+  public Post() {
+  }
+
+  public Post(int id) {
+    this.id = id;
+  }
+
   public int getId() {
     return id;
   }

From cd1bb3938b61b88535a53431332a2e2b56ae64ab Mon Sep 17 00:00:00 2001
From: JiHongYuan <1206429202@qq.com>
Date: Fri, 17 Dec 2021 09:52:09 +0800
Subject: [PATCH 3/4] Revert "Update Test Cased"

This reverts commit 748d296a57c63af21de9cf2d2dafa6c4a8416098.
---
 src/test/java/org/apache/ibatis/builder/xsd/BlogMapper.xml | 3 ---
 src/test/java/org/apache/ibatis/domain/blog/DraftPost.java | 6 ------
 src/test/java/org/apache/ibatis/domain/blog/Post.java      | 7 -------
 3 files changed, 16 deletions(-)

diff --git a/src/test/java/org/apache/ibatis/builder/xsd/BlogMapper.xml b/src/test/java/org/apache/ibatis/builder/xsd/BlogMapper.xml
index 255a03536ea..d01680da2e7 100644
--- a/src/test/java/org/apache/ibatis/builder/xsd/BlogMapper.xml
+++ b/src/test/java/org/apache/ibatis/builder/xsd/BlogMapper.xml
@@ -83,9 +83,6 @@
   </resultMap>
 
   <resultMap id="joinedPost" type="org.apache.ibatis.domain.blog.Post">
-    <constructor>
-      <idArg column="post_id" name="id"/>
-    </constructor>
     <id property="id" column="post_id"/>
     <result property="subject" column="post_subject"/>
     <association property="author" resultMap="joinedAuthor"/>
diff --git a/src/test/java/org/apache/ibatis/domain/blog/DraftPost.java b/src/test/java/org/apache/ibatis/domain/blog/DraftPost.java
index fc30d70f773..0ab0d7167bf 100644
--- a/src/test/java/org/apache/ibatis/domain/blog/DraftPost.java
+++ b/src/test/java/org/apache/ibatis/domain/blog/DraftPost.java
@@ -16,10 +16,4 @@
 package org.apache.ibatis.domain.blog;
 
 public class DraftPost extends Post {
-  public DraftPost() {
-  }
-
-  public DraftPost(int id) {
-    super(id);
-  }
 }
diff --git a/src/test/java/org/apache/ibatis/domain/blog/Post.java b/src/test/java/org/apache/ibatis/domain/blog/Post.java
index d82238a56f6..345b43c01b6 100644
--- a/src/test/java/org/apache/ibatis/domain/blog/Post.java
+++ b/src/test/java/org/apache/ibatis/domain/blog/Post.java
@@ -30,13 +30,6 @@ public class Post {
   private List<Comment> comments;
   private List<Tag> tags;
 
-  public Post() {
-  }
-
-  public Post(int id) {
-    this.id = id;
-  }
-
   public int getId() {
     return id;
   }

From defbb8e2d309b74b652b5f87336019d3e8a30e60 Mon Sep 17 00:00:00 2001
From: JiHongYuan <1206429202@qq.com>
Date: Fri, 17 Dec 2021 10:00:15 +0800
Subject: [PATCH 4/4] Add Constructor Test Case

---
 .../org/apache/ibatis/builder/BlogMapper.xml  | 45 ++++++++++++++++++-
 .../apache/ibatis/builder/xsd/BlogMapper.xml  | 45 ++++++++++++++++++-
 .../apache/ibatis/domain/blog/DraftPost.java  |  7 +++
 .../org/apache/ibatis/domain/blog/Post.java   |  7 +++
 .../domain/blog/mappers/BlogMapper.java       |  2 +
 .../apache/ibatis/session/SqlSessionTest.java |  9 ++++
 6 files changed, 113 insertions(+), 2 deletions(-)

diff --git a/src/test/java/org/apache/ibatis/builder/BlogMapper.xml b/src/test/java/org/apache/ibatis/builder/BlogMapper.xml
index a83bc33dffa..56352bb21df 100644
--- a/src/test/java/org/apache/ibatis/builder/BlogMapper.xml
+++ b/src/test/java/org/apache/ibatis/builder/BlogMapper.xml
@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8" ?>
 <!--
 
-       Copyright 2009-2019 the original author or authors.
+       Copyright 2009-2021 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.
@@ -94,6 +94,15 @@
     </discriminator>
   </resultMap>
 
+  <resultMap id="joinedConstructorPost" type="org.apache.ibatis.domain.blog.Post">
+    <constructor>
+      <idArg column="post_id" name="id"/>
+    </constructor>
+    <discriminator javaType="int" column="draft">
+      <case value="1" resultMap="draftPost"/>
+    </discriminator>
+  </resultMap>
+
   <resultMap id="draftPost" type="org.apache.ibatis.domain.blog.DraftPost" extends="joinedPost"/>
 
   <resultMap id="blogJoinedWithPostsAndAuthor" type="Blog">
@@ -149,6 +158,40 @@
     where B.id = #{id}
   </select>
 
+  <select id="selectBlogJoinedConstructorWithPostsAndAuthor" parameterType="int" resultMap="joinedConstructorPost">
+    select
+      B.id as blog_id,
+      B.title as blog_title,
+      B.author_id as blog_author_id,
+      A.id as author_id,
+      A.username as author_username,
+      A.password as author_password,
+      A.email as author_email,
+      A.bio as author_bio,
+      A.favourite_section as author_favourite_section,
+      P.id as post_id,
+      P.blog_id as post_blog_id,
+      P.author_id as post_author_id,
+      P.created_on as post_created_on,
+      P.section as post_section,
+      P.subject as post_subject,
+      P.draft as draft,
+      P.body as post_body,
+      C.id as comment_id,
+      C.post_id as comment_post_id,
+      C.name as comment_name,
+      C.comment as comment_text,
+      T.id as tag_id,
+      T.name as tag_name
+    from Blog B
+    left outer join Author A on B.author_id = A.id
+    left outer join Post P on B.id = P.blog_id
+    left outer join Comment C on P.id = C.post_id
+    left outer join Post_Tag PT on PT.post_id = P.id
+    left outer join Tag T on PT.tag_id = T.id
+    where B.id = #{id}
+  </select>
+
   <select id="selectAllPosts" resultType="hashmap">
     select * from post order by id
   </select>
diff --git a/src/test/java/org/apache/ibatis/builder/xsd/BlogMapper.xml b/src/test/java/org/apache/ibatis/builder/xsd/BlogMapper.xml
index d01680da2e7..14e37ccd70e 100644
--- a/src/test/java/org/apache/ibatis/builder/xsd/BlogMapper.xml
+++ b/src/test/java/org/apache/ibatis/builder/xsd/BlogMapper.xml
@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8" ?>
 <!--
 
-       Copyright 2009-2019 the original author or authors.
+       Copyright 2009-2021 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.
@@ -93,6 +93,15 @@
     </discriminator>
   </resultMap>
 
+  <resultMap id="joinedConstructorPost" type="org.apache.ibatis.domain.blog.Post">
+    <constructor>
+      <idArg column="post_id" name="id"/>
+    </constructor>
+    <discriminator javaType="int" column="draft">
+      <case value="1" resultMap="draftPost"/>
+    </discriminator>
+  </resultMap>
+
   <resultMap id="draftPost" type="org.apache.ibatis.domain.blog.DraftPost" extends="joinedPost"/>
 
   <resultMap id="blogJoinedWithPostsAndAuthor" type="Blog">
@@ -148,6 +157,40 @@
     where B.id = #{id}
   </select>
 
+  <select id="selectBlogJoinedConstructorWithPostsAndAuthor" parameterType="int" resultMap="joinedConstructorPost">
+    select
+    B.id as blog_id,
+    B.title as blog_title,
+    B.author_id as blog_author_id,
+    A.id as author_id,
+    A.username as author_username,
+    A.password as author_password,
+    A.email as author_email,
+    A.bio as author_bio,
+    A.favourite_section as author_favourite_section,
+    P.id as post_id,
+    P.blog_id as post_blog_id,
+    P.author_id as post_author_id,
+    P.created_on as post_created_on,
+    P.section as post_section,
+    P.subject as post_subject,
+    P.draft as draft,
+    P.body as post_body,
+    C.id as comment_id,
+    C.post_id as comment_post_id,
+    C.name as comment_name,
+    C.comment as comment_text,
+    T.id as tag_id,
+    T.name as tag_name
+    from Blog B
+    left outer join Author A on B.author_id = A.id
+    left outer join Post P on B.id = P.blog_id
+    left outer join Comment C on P.id = C.post_id
+    left outer join Post_Tag PT on PT.post_id = P.id
+    left outer join Tag T on PT.tag_id = T.id
+    where B.id = #{id}
+  </select>
+
   <select id="selectAllPosts" resultType="hashmap">
     select * from post order by id
   </select>
diff --git a/src/test/java/org/apache/ibatis/domain/blog/DraftPost.java b/src/test/java/org/apache/ibatis/domain/blog/DraftPost.java
index 0ab0d7167bf..a12873025da 100644
--- a/src/test/java/org/apache/ibatis/domain/blog/DraftPost.java
+++ b/src/test/java/org/apache/ibatis/domain/blog/DraftPost.java
@@ -16,4 +16,11 @@
 package org.apache.ibatis.domain.blog;
 
 public class DraftPost extends Post {
+
+  public DraftPost() {
+  }
+
+  public DraftPost(int id) {
+    super(id);
+  }
 }
diff --git a/src/test/java/org/apache/ibatis/domain/blog/Post.java b/src/test/java/org/apache/ibatis/domain/blog/Post.java
index 345b43c01b6..d82238a56f6 100644
--- a/src/test/java/org/apache/ibatis/domain/blog/Post.java
+++ b/src/test/java/org/apache/ibatis/domain/blog/Post.java
@@ -30,6 +30,13 @@ public class Post {
   private List<Comment> comments;
   private List<Tag> tags;
 
+  public Post() {
+  }
+
+  public Post(int id) {
+    this.id = id;
+  }
+
   public int getId() {
     return id;
   }
diff --git a/src/test/java/org/apache/ibatis/domain/blog/mappers/BlogMapper.java b/src/test/java/org/apache/ibatis/domain/blog/mappers/BlogMapper.java
index 91ea629cbfb..0ad1b399fc6 100644
--- a/src/test/java/org/apache/ibatis/domain/blog/mappers/BlogMapper.java
+++ b/src/test/java/org/apache/ibatis/domain/blog/mappers/BlogMapper.java
@@ -28,4 +28,6 @@ public interface BlogMapper {
 
   List<Map> selectAllPosts(RowBounds rowBounds, Object param);
 
+  List<Map> selectBlogJoinedConstructorWithPostsAndAuthor(int id);
+
 }
diff --git a/src/test/java/org/apache/ibatis/session/SqlSessionTest.java b/src/test/java/org/apache/ibatis/session/SqlSessionTest.java
index b8c1214ffc7..40e25c4de57 100644
--- a/src/test/java/org/apache/ibatis/session/SqlSessionTest.java
+++ b/src/test/java/org/apache/ibatis/session/SqlSessionTest.java
@@ -661,6 +661,15 @@ void shouldLimitResultsUsingMapperClass() {
     }
   }
 
+  @Test
+  void shouldNotNPEResultsUsingMapperClass() {
+    try (SqlSession session = sqlMapper.openSession()) {
+      BlogMapper mapper = session.getMapper(BlogMapper.class);
+      List<Map> postsAndAuthor = mapper.selectBlogJoinedConstructorWithPostsAndAuthor(1);
+      assertNotNull(postsAndAuthor);
+    }
+  }
+
   private static class TestResultHandler implements ResultHandler {
     int count = 0;
     @Override