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src/test/java/com/example/demo/util/MyBatisGeneratorUtilsTest.java

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+package com.example.demo.util;
+
+import com.example.demo.entity.Author;
+import com.example.demo.entity.Book;
+import org.junit.jupiter.api.Test;
+
+import java.util.Arrays;
+import java.util.List;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+class MyBatisGeneratorUtilsTest {
+
+    @Test
+    void testGenerateSql_Simple() {
+        List<String> fields = Arrays.asList("title", "isbn");
+        String sql = MyBatisGeneratorUtils.generateSql(Book.class, fields);
+        
+        System.out.println("=== Simple SQL ===");
+        System.out.println(sql);
+        
+        assertTrue(sql.contains("SELECT"));
+        // Root fields should NOT have prefix (to match standard ResultMap)
+        // book.title AS title
+        assertTrue(sql.contains("book.title AS title"));
+        assertTrue(sql.contains("FROM book book"));
+    }
+
+    @Test
+    void testGenerateSql_OneToMany_List() {
+        // Author -> List<Book>
+        // Request: author.name, author.books.title
+        List<String> fields = Arrays.asList("name", "books.title");
+        String sql = MyBatisGeneratorUtils.generateSql(Author.class, fields);
+        
+        System.out.println("=== OneToMany List SQL ===");
+        System.out.println(sql);
+        
+        // Root: author
+        assertTrue(sql.contains("FROM author author"));
+        assertTrue(sql.contains("author.name AS name"));
+        // Check Forced ID
+        assertTrue(sql.contains("author.id AS id"));
+        
+        // Join: author -> book (OneToMany)
+        // mappedBy="author" in Author means Book has "author" field.
+        // Join condition should be: author.id = books.author_id
+        assertTrue(sql.contains("LEFT JOIN book author$books"));
+        
+        // Correct Join Condition for OneToMany
+        // author.id = author$books.author_id (assuming default convention or @JoinColumn on Book.author)
+        // Book.java: @JoinColumn(name = "author_id") private Author author;
+        assertTrue(sql.contains("author.id = author$books.author_id"));
+        
+        // Check Child Columns
+        assertTrue(sql.contains("author$books.title AS books$title"));
+        // Check Child Forced ID
+        assertTrue(sql.contains("author$books.id AS books$id"));
+    }
+
+    @Test
+    void testGenerateMapperXml() {
+        List<String> fields = Arrays.asList("title", "author.name", "author.books");
+        String xml = MyBatisGeneratorUtils.generateMapperXml(Book.class, "com.example.demo.mapper.BookMapper", fields);
+        
+        System.out.println("=== Generated Mapper XML ===");
+        System.out.println(xml);
+        
+        assertTrue(xml.contains("<mapper namespace=\"com.example.demo.mapper.BookMapper\">"));
+        assertTrue(xml.contains("<resultMap id=\"BookMap\""));
+        assertTrue(xml.contains("<resultMap id=\"AuthorMap\""));
+        
+        // Verify BookMap -> AuthorMap association
+        assertTrue(xml.contains("<association property=\"author\" resultMap=\"AuthorMap\" columnPrefix=\"author$\"/>"));
+        
+        // Verify AuthorMap -> Books collection
+        assertTrue(xml.contains("<collection property=\"books\" resultMap=\"BookMap\" columnPrefix=\"books$\"/>"));
+        
+        // Verify SQL is included
+        assertTrue(xml.contains("SELECT"));
+        // Use column name in alias (publish_month)
+        assertTrue(xml.contains("book$author$books.publish_month AS author$books$publish_month"));
+    }
+
+    @Test
+    void testGenerateSql_NestedJoin() {
+        List<String> fields = Arrays.asList("title", "author.name", "author.region.name");
+        String sql = MyBatisGeneratorUtils.generateSql(Book.class, fields);
+
+        System.out.println("=== Nested Join SQL ===");
+        System.out.println(sql);
+
+        // Verify Joins
+        assertTrue(sql.contains("LEFT JOIN author book$author"));
+        assertTrue(sql.contains("LEFT JOIN region book$author$region"));
+        
+        // Verify Columns
+        // Child fields SHOULD have relative prefix
+        // book$author.name AS author$name
+        assertTrue(sql.contains("book$author.name AS author$name"));
+        // book$author$region.name AS author$region$name
+        assertTrue(sql.contains("book$author$region.name AS author$region$name"));
+    }
+    
+    @Test
+    void testGenerateSql_ExpandObject() {
+        // "periodical" is an object, should expand to periodical.name, periodical.publishMonth etc.
+        List<String> fields = Arrays.asList("title", "periodical");
+        String sql = MyBatisGeneratorUtils.generateSql(Book.class, fields);
+
+        System.out.println("=== Expand Object SQL ===");
+        System.out.println(sql);
+
+        assertTrue(sql.contains("LEFT JOIN periodical book$periodical"));
+        assertTrue(sql.contains("book$periodical.name AS periodical$name"));
+        // Use column name in alias: publish_month
+        assertTrue(sql.contains("book$periodical.publish_month AS periodical$publish_month"));
+    }
+    @Test
+    void testGenerateSql_CompositeKeyJoin() {
+        List<String> fields = Arrays.asList("title", "periodical.name");
+        String sql = MyBatisGeneratorUtils.generateSql(Book.class, fields);
+
+        System.out.println("=== Composite Key Join SQL ===");
+        System.out.println(sql);
+
+        // Verify Composite Join Condition (publisher_id AND publish_month)
+        assertTrue(sql.contains("LEFT JOIN periodical book$periodical"));
+        assertTrue(sql.contains("book.publisher_id = book$periodical.publisher_id"));
+        assertTrue(sql.contains("book.publish_month = book$periodical.publish_month"));
+    }
+}