Add the ability to generate a camel cased alias for a column

CHANGELOG.md

@@ -7,6 +7,7 @@ This log will detail notable changes to MyBatis Dynamic SQL. Full details are av
 ### Added
 
 - Added a new sort specification that is useful in selects with joins ([#269](https://github.com/mybatis/mybatis-dynamic-sql/pull/269))
+- Added the capability to generate a camel cased alias for a column ([#272](https://github.com/mybatis/mybatis-dynamic-sql/issues/272))
 
 ## Release 1.2.1 - September 29, 2020
 

src/main/java/org/mybatis/dynamic/sql/SqlColumn.java

@@ -22,6 +22,7 @@
 import org.jetbrains.annotations.NotNull;
 import org.mybatis.dynamic.sql.render.RenderingStrategy;
 import org.mybatis.dynamic.sql.render.TableAliasCalculator;
+import org.mybatis.dynamic.sql.util.StringUtilities;
 
 public class SqlColumn<T> implements BindableColumn<T>, SortSpecification {
 
@@ -85,6 +86,22 @@ public SqlColumn<T> as(String alias) {
         return b.withAlias(alias).build();
     }
 
+    /**
+     * Set an alias with a camel cased string based on the column name. The can be useful for queries using
+     * the {@link org.mybatis.dynamic.sql.util.mybatis3.CommonSelectMapper} where the columns are placed into
+     * a map based on the column name returned from the database.
+     *
+     * <p>A camel case string is mixed case, and most databases do not support unquoted mixed case strings
+     * as identifiers. Therefore the generated alias will be surrounded by double quotes thereby making it a
+     * quoted identifier. Most databases will respect quoted mixed case identifiers.
+     *
+     * @return a new column aliased with a camel case version of the column name
+     */
+    public SqlColumn<T> asCamelCase() {
+        Builder<T> b = copy();
+        return b.withAlias("\"" + StringUtilities.toCamelCase(name) + "\"").build(); //$NON-NLS-1$ //$NON-NLS-2$
+    }
+
     @Override
     public boolean isDescending() {
         return isDescending;

src/main/java/org/mybatis/dynamic/sql/util/StringUtilities.java

@@ -40,4 +40,28 @@ static String spaceBefore(String in) {
     static String safelyUpperCase(String s) {
         return s == null ? null : s.toUpperCase();
     }
+
+    static String toCamelCase(String inputString) {
+        StringBuilder sb = new StringBuilder();
+
+        boolean nextUpperCase = false;
+
+        for (int i = 0; i < inputString.length(); i++) {
+            char c = inputString.charAt(i);
+            if (Character.isLetterOrDigit(c)) {
+                if (nextUpperCase) {
+                    sb.append(Character.toUpperCase(c));
+                    nextUpperCase = false;
+                } else {
+                    sb.append(Character.toLowerCase(c));
+                }
+            } else {
+                if (sb.length() > 0) {
+                    nextUpperCase = true;
+                }
+            }
+        }
+
+        return sb.toString();
+    }
 }

src/test/java/examples/animal/data/CommonSelectMapperTest.java

@@ -81,15 +81,15 @@ void setup() throws Exception {
     void testGeneralSelectOne() {
         try (SqlSession sqlSession = sqlSessionFactory.openSession()) {
             CommonSelectMapper mapper = sqlSession.getMapper(CommonSelectMapper.class);
-            SelectStatementProvider selectStatement = select(id, animalName)
+            SelectStatementProvider selectStatement = select(id.asCamelCase(), animalName.asCamelCase())
                     .from(animalData)
                     .where(id, isEqualTo(1))
                     .build()
                     .render(RenderingStrategies.MYBATIS3);
             Map<String, Object> row = mapper.selectOneMappedRow(selectStatement);
 
-            assertThat(row).containsEntry("ID", 1);
-            assertThat(row).containsEntry("ANIMAL_NAME", "Lesser short-tailed shrew");
+            assertThat(row).containsEntry("id", 1);
+            assertThat(row).containsEntry("animalName", "Lesser short-tailed shrew");
         }
     }
 

src/test/java/org/mybatis/dynamic/sql/util/StringUtilitiesTest.java

@@ -0,0 +1,41 @@
+/*
+ *    Copyright 2016-2020 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.
+ */
+package org.mybatis.dynamic.sql.util;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.jupiter.api.Test;
+
+class StringUtilitiesTest {
+
+    @Test
+    void testInitialUnderscore() {
+        String input = "_USER";
+        assertThat(StringUtilities.toCamelCase(input)).isEqualTo("user");
+    }
+
+    @Test
+    void testSpace() {
+        String input = "USER NAME";
+        assertThat(StringUtilities.toCamelCase(input)).isEqualTo("userName");
+    }
+
+    @Test
+    void testNumeric() {
+        String input = "USER%NAME%3";
+        assertThat(StringUtilities.toCamelCase(input)).isEqualTo("userName3");
+    }
+}