Step 2 - Define sort specification interface for ORDER BY

Author: jeffgbutler

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

@@ -0,0 +1,28 @@
+/**
+ *    Copyright 2016-2017 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;
+
+/**
+ * Defines attributes of columns that are necessary for rendering an order by expression.
+ * 
+ * @author Jeff Butler
+ *
+ */
+public interface SortSpecification {
+    SortSpecification as(String alias);
+    String aliasOrName();
+    boolean isDescending();
+}

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

@@ -21,7 +21,7 @@
 
 import org.mybatis.dynamic.sql.render.TableAliasCalculator;
 
-public class SqlColumn<T> implements BindableColumn<T> {
+public class SqlColumn<T> implements BindableColumn<T>, SortSpecification {
 
     protected String name;
     protected SqlTable table;
@@ -65,10 +65,23 @@ public Optional<String> typeHandler() {
         return typeHandler;
     }
 
-    public SqlColumn<T> descending() {
-        SqlColumn<T> column = new SqlColumn<>(this);
-        column.isDescending = true;
-        return column;
+    public SortSpecification descending() {
+        return new SortSpecification() {
+            @Override
+            public SortSpecification as(String alias) {
+                return SqlColumn.this.as(alias);
+            }
+            
+            @Override
+            public boolean isDescending() {
+                return true;
+            }
+            
+            @Override
+            public String aliasOrName() {
+                return SqlColumn.this.aliasOrName();
+            }
+        };
     }
 
     @Override
@@ -78,10 +91,16 @@ public SqlColumn<T> as(String alias) {
         return column;
     }
 
+    @Override
     public boolean isDescending() {
         return isDescending;
     }
 
+    @Override
+    public String aliasOrName() {
+        return alias.orElse(name);
+    }
+    
     @Override
     public String applyTableAliasToName(TableAliasCalculator tableAliasCalculator) {
         return tableAliasCalculator.aliasForColumn(table)

src/main/java/org/mybatis/dynamic/sql/select/OrderByModel.java

@@ -21,20 +21,20 @@
 import java.util.function.Function;
 import java.util.stream.Stream;
 
-import org.mybatis.dynamic.sql.SqlColumn;
+import org.mybatis.dynamic.sql.SortSpecification;
 
 public class OrderByModel {
-    private List<SqlColumn<?>> columns = new ArrayList<>();
+    private List<SortSpecification> columns = new ArrayList<>();
 
-    private OrderByModel(List<SqlColumn<?>> columns) {
+    private OrderByModel(List<SortSpecification> columns) {
         this.columns.addAll(columns);
     }
 
-    public <R> Stream<R> mapColumns(Function<SqlColumn<?>, R> mapper) {
+    public <R> Stream<R> mapColumns(Function<SortSpecification, R> mapper) {
         return columns.stream().map(mapper);
     }
 
-    public static OrderByModel of(SqlColumn<?>...columns) {
+    public static OrderByModel of(SortSpecification...columns) {
         return new OrderByModel(Arrays.asList(columns));
     }
 }

src/main/java/org/mybatis/dynamic/sql/select/QueryExpressionDSL.java

@@ -23,8 +23,8 @@
 import java.util.Objects;
 
 import org.mybatis.dynamic.sql.BindableColumn;
+import org.mybatis.dynamic.sql.SortSpecification;
 import org.mybatis.dynamic.sql.BasicColumn;
-import org.mybatis.dynamic.sql.SqlColumn;
 import org.mybatis.dynamic.sql.SqlCriterion;
 import org.mybatis.dynamic.sql.SqlTable;
 import org.mybatis.dynamic.sql.VisitableCondition;
@@ -174,7 +174,7 @@ public GroupByFinisher groupBy(BasicColumn...columns) {
             return new GroupByFinisher();
         }
 
-        public SelectDSL orderBy(SqlColumn<?>...columns) {
+        public SelectDSL orderBy(SortSpecification...columns) {
             selectModelBuilder.addQueryExpression(buildModel());
             selectModelBuilder.setOrderByModel(OrderByModel.of(columns));
             return selectModelBuilder;
@@ -203,7 +203,7 @@ public UnionBuilder union() {
             return new UnionBuilder();
         }
 
-        public SelectDSL orderBy(SqlColumn<?>...columns) {
+        public SelectDSL orderBy(SortSpecification...columns) {
             whereModel = buildWhereModel();
             selectModelBuilder.addQueryExpression(buildModel());
             selectModelBuilder.setOrderByModel(OrderByModel.of(columns));
@@ -358,7 +358,7 @@ public JoinSpecificationStarter fullJoin(SqlTable joinTable, String tableAlias)
             return fullJoin(joinTable);
         }
 
-        public SelectDSL orderBy(SqlColumn<?>...columns) {
+        public SelectDSL orderBy(SortSpecification...columns) {
             joinModel = buildJoinModel();
             selectModelBuilder.addQueryExpression(buildModel());
             selectModelBuilder.setOrderByModel(OrderByModel.of(columns));
@@ -367,7 +367,7 @@ public SelectDSL orderBy(SqlColumn<?>...columns) {
     }
 
     public class GroupByFinisher implements Buildable<SelectModel> {
-        public SelectDSL orderBy(SqlColumn<?>...columns) {
+        public SelectDSL orderBy(SortSpecification...columns) {
             selectModelBuilder.setOrderByModel(OrderByModel.of(columns));
             return selectModelBuilder;
         }

src/main/java/org/mybatis/dynamic/sql/select/render/SelectRenderer.java

@@ -19,7 +19,7 @@
 import java.util.Optional;
 import java.util.concurrent.atomic.AtomicInteger;
 
-import org.mybatis.dynamic.sql.SqlColumn;
+import org.mybatis.dynamic.sql.SortSpecification;
 import org.mybatis.dynamic.sql.render.RenderingStrategy;
 import org.mybatis.dynamic.sql.select.OrderByModel;
 import org.mybatis.dynamic.sql.select.QueryExpressionModel;
@@ -63,8 +63,8 @@ private String renderOrderBy(OrderByModel orderByModel) {
                 .collect(CustomCollectors.joining(", ", "order by ", "")); //$NON-NLS-1$ //$NON-NLS-2$ //$NON-NLS-3$
     }
 
-    private String orderByPhrase(SqlColumn<?> column) {
-        String phrase = column.alias().orElse(column.name());
+    private String orderByPhrase(SortSpecification column) {
+        String phrase = column.aliasOrName();
         if (column.isDescending()) {
             phrase = phrase + " DESC"; //$NON-NLS-1$
         }