Some abstraction for the count functions

Author: jeffgbutler

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/Count.java

@@ -15,27 +15,18 @@
  */
 package org.mybatis.dynamic.sql.select.aggregate;
 
-import java.sql.JDBCType;
 import java.util.Objects;
-import java.util.Optional;
 
 import org.mybatis.dynamic.sql.BasicColumn;
-import org.mybatis.dynamic.sql.BindableColumn;
 import org.mybatis.dynamic.sql.render.TableAliasCalculator;
 
-public class Count implements BindableColumn<Long> {
+public class Count extends AbstractCount<Count> {
 
     private final BasicColumn column;
-    private final String alias;
-
-    private Count(BasicColumn column) {
-        this.column = Objects.requireNonNull(column);
-        alias = null;
-    }
 
     private Count(BasicColumn column, String alias) {
+        super(alias);
         this.column = Objects.requireNonNull(column);
-        this.alias = alias;
     }
 
     @Override
@@ -44,21 +35,11 @@ public String renderWithTableAlias(TableAliasCalculator tableAliasCalculator) {
     }
 
     @Override
-    public Optional<String> alias() {
-        return Optional.ofNullable(alias);
-    }
-
-    @Override
-    public Count as(String alias) {
+    protected Count copyWithAlias(String alias) {
         return new Count(column, alias);
     }
 
-    @Override
-    public Optional<JDBCType> jdbcType() {
-        return Optional.of(JDBCType.BIGINT);
-    }
-
     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

@@ -15,29 +15,16 @@
  */
 package org.mybatis.dynamic.sql.select.aggregate;
 
-import java.sql.JDBCType;
-import java.util.Optional;
-
-import org.mybatis.dynamic.sql.BindableColumn;
 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
- * BindableColumn directly.
- *  
- * @author Jeff Butler
- */
-public class CountAll implements BindableColumn<Long> {
-    
-    private final String alias;
+public class CountAll extends AbstractCount<CountAll> {
 
     public CountAll() {
-        alias = null;
+        super(null);
     }
 
     private CountAll(String alias) {
-        this.alias = alias;
+        super(alias);
     }
 
     @Override
@@ -46,17 +33,7 @@ public String renderWithTableAlias(TableAliasCalculator tableAliasCalculator) {
     }
 
     @Override
-    public Optional<String> alias() {
-        return Optional.ofNullable(alias);
-    }
-
-    @Override
-    public CountAll as(String alias) {
+    protected CountAll copyWithAlias(String alias) {
         return new CountAll(alias);
     }
-
-    @Override
-    public Optional<JDBCType> jdbcType() {
-        return Optional.of(JDBCType.BIGINT);
-    }
 }

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

@@ -15,27 +15,18 @@
  */
 package org.mybatis.dynamic.sql.select.aggregate;
 
-import java.sql.JDBCType;
 import java.util.Objects;
-import java.util.Optional;
 
 import org.mybatis.dynamic.sql.BasicColumn;
-import org.mybatis.dynamic.sql.BindableColumn;
 import org.mybatis.dynamic.sql.render.TableAliasCalculator;
 
-public class CountDistinct implements BindableColumn<Long> {
+public class CountDistinct extends AbstractCount<CountDistinct> {
 
     private final BasicColumn column;
-    private final String alias;
-
-    private CountDistinct(BasicColumn column) {
-        this.column = Objects.requireNonNull(column);
-        alias = null;
-    }
 
     private CountDistinct(BasicColumn column, String alias) {
+        super(alias);
         this.column = Objects.requireNonNull(column);
-        this.alias = alias;
     }
 
     @Override
@@ -44,21 +35,11 @@ public String renderWithTableAlias(TableAliasCalculator tableAliasCalculator) {
     }
 
     @Override
-    public Optional<String> alias() {
-        return Optional.ofNullable(alias);
-    }
-
-    @Override
-    public CountDistinct as(String alias) {
+    public CountDistinct copyWithAlias(String alias) {
         return new CountDistinct(column, alias);
     }
 
-    @Override
-    public Optional<JDBCType> jdbcType() {
-        return Optional.of(JDBCType.BIGINT);
-    }
-
     public static CountDistinct of(BasicColumn column) {
-        return new CountDistinct(column);
+        return new CountDistinct(column, null);
     }
 }