Refactor Aggregates to Behave Like Functions

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

@@ -331,19 +331,19 @@ static CountDistinct countDistinct(BasicColumn column) {
         return CountDistinct.of(column);
     }
 
-    static Max max(BasicColumn column) {
+    static <T> Max<T> max(BindableColumn<T> column) {
         return Max.of(column);
     }
 
-    static Min min(BasicColumn column) {
+    static <T> Min<T> min(BindableColumn<T> column) {
         return Min.of(column);
     }
 
-    static Avg avg(BasicColumn column) {
+    static <T> Avg<T> avg(BindableColumn<T> column) {
         return Avg.of(column);
     }
 
-    static Sum sum(BasicColumn column) {
+    static <T> Sum<T> sum(BindableColumn<T> column) {
         return Sum.of(column);
     }
 

src/main/java/org/mybatis/dynamic/sql/select/aggregate/AbstractAggregate.java

@@ -23,11 +23,15 @@
 
 /**
  * This class is the base class for aggregate functions.
- * 
+ *
+ * @deprecated  in favor of {@link org.mybatis.dynamic.sql.select.function.AbstractUniTypeFunction} as there is
+ *     virtually no difference between an aggregate and a function
+ *
  * @author Jeff Butler
  *
  * @param <T> the subclass type
  */
+@Deprecated
 public abstract class AbstractAggregate<T extends AbstractAggregate<T>> implements BasicColumn {
     protected final BasicColumn column;
     protected String alias;

src/main/java/org/mybatis/dynamic/sql/select/aggregate/AbstractCount.java

@@ -0,0 +1,46 @@
+/*
+ *    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.select.aggregate;
+
+import java.util.Optional;
+import org.mybatis.dynamic.sql.BindableColumn;
+
+/**
+ * Count functions are implemented differently than the other aggregates. This is primarily to preserve
+ * backwards compatibility. Count functions are configured as BindableColumns of type Long
+ * as it is assumed that the count functions always return a number.
+ *
+ * @param <T> the subtype of this class
+ */
+public abstract class AbstractCount<T extends AbstractCount<T>> implements BindableColumn<Long> {
+    private final String alias;
+
+    protected AbstractCount(String alias) {
+        this.alias = alias;
+    }
+
+    @Override
+    public Optional<String> alias() {
+        return Optional.ofNullable(alias);
+    }
+
+    @Override
+    public T as(String alias) {
+        return copyWithAlias(alias);
+    }
+
+    protected abstract T copyWithAlias(String alias);
+}

src/main/java/org/mybatis/dynamic/sql/select/aggregate/Avg.java

@@ -15,25 +15,27 @@
  */
 package org.mybatis.dynamic.sql.select.aggregate;
 
-import org.mybatis.dynamic.sql.BasicColumn;
+import org.mybatis.dynamic.sql.BindableColumn;
+import org.mybatis.dynamic.sql.render.TableAliasCalculator;
+import org.mybatis.dynamic.sql.select.function.AbstractUniTypeFunction;
 
-public class Avg extends AbstractAggregate<Avg> {
+public class Avg<T> extends AbstractUniTypeFunction<T, Avg<T>> {
 
-    private Avg(BasicColumn column) {
+    private Avg(BindableColumn<T> column) {
         super(column);
     }
-    
+
     @Override
-    protected String render(String columnName) {
-        return "avg(" + columnName + ")"; //$NON-NLS-1$ //$NON-NLS-2$
+    public String renderWithTableAlias(TableAliasCalculator tableAliasCalculator) {
+        return "avg(" + column.renderWithTableAlias(tableAliasCalculator) + ")"; //$NON-NLS-1$ //$NON-NLS-2$
     }
 
     @Override
-    protected Avg copy() {
-        return new Avg(column);
+    protected Avg<T> copy() {
+        return new Avg<>(column);
     }
 
-    public static Avg of(BasicColumn column) {
-        return new Avg(column);
+    public static <T> Avg<T> of(BindableColumn<T> column) {
+        return new Avg<>(column);
     }
 }

src/main/java/org/mybatis/dynamic/sql/select/aggregate/Count.java

@@ -15,25 +15,31 @@
  */
 package org.mybatis.dynamic.sql.select.aggregate;
 
+import java.util.Objects;
+
 import org.mybatis.dynamic.sql.BasicColumn;
+import org.mybatis.dynamic.sql.render.TableAliasCalculator;
+
+public class Count extends AbstractCount<Count> {
+
+    private final BasicColumn column;
 
-public class Count extends AbstractAggregate<Count> {
-
-    private Count(BasicColumn column) {
-        super(column);
+    private Count(BasicColumn column, String alias) {
+        super(alias);
+        this.column = Objects.requireNonNull(column);
     }
-    
+
     @Override
-    protected String render(String columnName) {
-        return "count(" + columnName + ")"; //$NON-NLS-1$ //$NON-NLS-2$
+    public String renderWithTableAlias(TableAliasCalculator tableAliasCalculator) {
+        return "count(" + column.renderWithTableAlias(tableAliasCalculator) + ")"; //$NON-NLS-1$ //$NON-NLS-2$
     }
 
     @Override
-    protected Count copy() {
-        return new Count(column);
+    protected Count copyWithAlias(String alias) {
+        return new Count(column, alias);
     }
-    
+
     public static Count of(BasicColumn column) {
-        return new Count(column);
+        return new Count(column, null);
     }
 }

src/main/java/org/mybatis/dynamic/sql/select/aggregate/CountAll.java

@@ -15,40 +15,25 @@
  */
 package org.mybatis.dynamic.sql.select.aggregate;
 
-import java.util.Optional;
-
-import org.mybatis.dynamic.sql.BasicColumn;
 import org.mybatis.dynamic.sql.render.TableAliasCalculator;
 
-/**
- * CountAll seems like the other aggregates, but it is special because there is no column.
- * Rather than dealing with a useless and confusing abstraction, we simply implement
- * BasicColumn directly.
- *  
- * @author Jeff Butler
- */
-public class CountAll implements BasicColumn {
-
-    private String alias;
+public class CountAll extends AbstractCount<CountAll> {
 
     public CountAll() {
-        super();
+        super(null);
     }
 
-    @Override
-    public String renderWithTableAlias(TableAliasCalculator tableAliasCalculator) {
-        return "count(*)"; //$NON-NLS-1$
+    private CountAll(String alias) {
+        super(alias);
     }
 
     @Override
-    public Optional<String> alias() {
-        return Optional.ofNullable(alias);
+    public String renderWithTableAlias(TableAliasCalculator tableAliasCalculator) {
+        return "count(*)"; //$NON-NLS-1$
     }
 
     @Override
-    public CountAll as(String alias) {
-        CountAll copy = new CountAll();
-        copy.alias = alias;
-        return copy;
+    protected CountAll copyWithAlias(String alias) {
+        return new CountAll(alias);
     }
 }

src/main/java/org/mybatis/dynamic/sql/select/aggregate/CountDistinct.java

@@ -15,25 +15,31 @@
  */
 package org.mybatis.dynamic.sql.select.aggregate;
 
+import java.util.Objects;
+
 import org.mybatis.dynamic.sql.BasicColumn;
+import org.mybatis.dynamic.sql.render.TableAliasCalculator;
+
+public class CountDistinct extends AbstractCount<CountDistinct> {
+
+    private final BasicColumn column;
 
-public class CountDistinct extends AbstractAggregate<CountDistinct> {
-
-    private CountDistinct(BasicColumn column) {
-        super(column);
+    private CountDistinct(BasicColumn column, String alias) {
+        super(alias);
+        this.column = Objects.requireNonNull(column);
     }
-    
+
     @Override
-    protected String render(String columnName) {
-        return "count(distinct " + columnName + ")"; //$NON-NLS-1$ //$NON-NLS-2$
+    public String renderWithTableAlias(TableAliasCalculator tableAliasCalculator) {
+        return "count(distinct " + column.renderWithTableAlias(tableAliasCalculator) + ")"; //$NON-NLS-1$ //$NON-NLS-2$
     }
 
     @Override
-    protected CountDistinct copy() {
-        return new CountDistinct(column);
+    public CountDistinct copyWithAlias(String alias) {
+        return new CountDistinct(column, alias);
     }
-    
+
     public static CountDistinct of(BasicColumn column) {
-        return new CountDistinct(column);
+        return new CountDistinct(column, null);
     }
 }

src/main/java/org/mybatis/dynamic/sql/select/aggregate/Max.java

@@ -15,25 +15,27 @@
  */
 package org.mybatis.dynamic.sql.select.aggregate;
 
-import org.mybatis.dynamic.sql.BasicColumn;
+import org.mybatis.dynamic.sql.BindableColumn;
+import org.mybatis.dynamic.sql.render.TableAliasCalculator;
+import org.mybatis.dynamic.sql.select.function.AbstractUniTypeFunction;
 
-public class Max extends AbstractAggregate<Max> {
+public class Max<T> extends AbstractUniTypeFunction<T, Max<T>> {
 
-    private Max(BasicColumn column) {
+    private Max(BindableColumn<T> column) {
         super(column);
     }
-    
+
     @Override
-    protected String render(String columnName) {
-        return "max(" + columnName + ")"; //$NON-NLS-1$ //$NON-NLS-2$
+    public String renderWithTableAlias(TableAliasCalculator tableAliasCalculator) {
+        return "max(" + column.renderWithTableAlias(tableAliasCalculator) + ")"; //$NON-NLS-1$ //$NON-NLS-2$
     }
 
     @Override
-    protected Max copy() {
-        return new Max(column);
+    protected Max<T> copy() {
+        return new Max<>(column);
     }
 
-    public static Max of(BasicColumn column) {
-        return new Max(column);
+    public static <T> Max<T> of(BindableColumn<T> column) {
+        return new Max<>(column);
     }
 }

src/main/java/org/mybatis/dynamic/sql/select/aggregate/Min.java

@@ -15,25 +15,27 @@
  */
 package org.mybatis.dynamic.sql.select.aggregate;
 
-import org.mybatis.dynamic.sql.BasicColumn;
+import org.mybatis.dynamic.sql.BindableColumn;
+import org.mybatis.dynamic.sql.render.TableAliasCalculator;
+import org.mybatis.dynamic.sql.select.function.AbstractUniTypeFunction;
 
-public class Min extends AbstractAggregate<Min> {
+public class Min<T> extends AbstractUniTypeFunction<T, Min<T>> {
 
-    private Min(BasicColumn column) {
+    private Min(BindableColumn<T> column) {
         super(column);
     }
-    
+
     @Override
-    protected String render(String columnName) {
-        return "min(" + columnName + ")"; //$NON-NLS-1$ //$NON-NLS-2$
+    public String renderWithTableAlias(TableAliasCalculator tableAliasCalculator) {
+        return "min(" + column.renderWithTableAlias(tableAliasCalculator) + ")"; //$NON-NLS-1$ //$NON-NLS-2$
     }
 
     @Override
-    protected Min copy() {
-        return new Min(column);
+    protected Min<T> copy() {
+        return new Min<>(column);
     }
 
-    public static Min of(BasicColumn column) {
-        return new Min(column);
+    public static <T> Min<T> of(BindableColumn<T> column) {
+        return new Min<>(column);
     }
 }

src/main/java/org/mybatis/dynamic/sql/select/aggregate/Sum.java

@@ -15,25 +15,27 @@
  */
 package org.mybatis.dynamic.sql.select.aggregate;
 
-import org.mybatis.dynamic.sql.BasicColumn;
+import org.mybatis.dynamic.sql.BindableColumn;
+import org.mybatis.dynamic.sql.render.TableAliasCalculator;
+import org.mybatis.dynamic.sql.select.function.AbstractUniTypeFunction;
 
-public class Sum extends AbstractAggregate<Sum> {
+public class Sum<T> extends AbstractUniTypeFunction<T, Sum<T>> {
 
-    private Sum(BasicColumn column) {
+    private Sum(BindableColumn<T> column) {
         super(column);
     }
-    
+
     @Override
-    protected String render(String columnName) {
-        return "sum(" + columnName + ")"; //$NON-NLS-1$ //$NON-NLS-2$
+    public String renderWithTableAlias(TableAliasCalculator tableAliasCalculator) {
+        return "sum(" + column.renderWithTableAlias(tableAliasCalculator) + ")"; //$NON-NLS-1$ //$NON-NLS-2$
     }
 
     @Override
-    protected Sum copy() {
-        return new Sum(column);
+    protected Sum<T> copy() {
+        return new Sum<>(column);
     }
 
-    public static Sum of(BasicColumn column) {
-        return new Sum(column);
+    public static <T> Sum<T> of(BindableColumn<T> column) {
+        return new Sum<>(column);
     }
 }