fix: 使用 join 联表查询一个对象，数据丢失。

mybatis-flex-core/src/main/java/com/mybatisflex/core/BaseMapper.java

@@ -1,4 +1,4 @@
-/**
+/*
  *  Copyright (c) 2022-2023, Mybatis-Flex (fuhai999@gmail.com).
  *  <p>
  *  Licensed under the Apache License, Version 2.0 (the "License");
@@ -345,8 +345,7 @@ public interface BaseMapper<T> {
      * @return entity 数据
      */
     default T selectOneByQuery(QueryWrapper queryWrapper) {
-        List<T> entities = selectListByQuery(queryWrapper.limit(1));
-        return (entities == null || entities.isEmpty()) ? null : entities.get(0);
+        return SqlUtil.getSelectOneResult(selectListByQuery(queryWrapper));
     }
 
 
@@ -358,8 +357,7 @@ public interface BaseMapper<T> {
      * @return 数据内容
      */
     default <R> R selectOneByQueryAs(QueryWrapper queryWrapper, Class<R> asType) {
-        List<R> entities = selectListByQueryAs(queryWrapper.limit(1), asType);
-        return (entities == null || entities.isEmpty()) ? null : entities.get(0);
+        return SqlUtil.getSelectOneResult(selectListByQueryAs(queryWrapper, asType));
     }
 
     /**
@@ -495,8 +493,7 @@ public interface BaseMapper<T> {
      * @return 数据量
      */
     default Object selectObjectByQuery(QueryWrapper queryWrapper) {
-        List<Object> objects = selectObjectListByQuery(queryWrapper.limit(1));
-        return objects == null || objects.isEmpty() ? null : objects.get(0);
+        return SqlUtil.getSelectOneResult(selectObjectListByQuery(queryWrapper));
     }
 
 

mybatis-flex-core/src/main/java/com/mybatisflex/core/util/SqlUtil.java

@@ -15,13 +15,18 @@
  */
 package com.mybatisflex.core.util;
 
+import org.apache.ibatis.exceptions.TooManyResultsException;
+import org.apache.ibatis.session.defaults.DefaultSqlSession;
+
 import java.time.LocalDateTime;
 import java.util.Date;
+import java.util.List;
 import java.util.regex.Matcher;
 
 public class SqlUtil {
 
-    private SqlUtil() {}
+    private SqlUtil() {
+    }
 
     public static void keepColumnSafely(String column) {
         if (StringUtil.isBlank(column)) {
@@ -108,4 +113,19 @@ public class SqlUtil {
         return sql;
     }
 
+    /**
+     * 搬运加改造 {@link DefaultSqlSession#selectOne(String, Object)}
+     */
+    public static <T> T getSelectOneResult(List<T> list) {
+        if (list == null || list.isEmpty()) {
+            return null;
+        }
+        int size = list.size();
+        if (size == 1) {
+            return list.get(0);
+        }
+        throw new TooManyResultsException(
+                "Expected one result (or null) to be returned by selectOne(), but found: " + size);
+    }
+
 }