refactor: 优化分页查询代码。

mybatis-flex-core/src/main/java/com/mybatisflex/core/BaseMapper.java

@@ -20,7 +20,10 @@ import com.mybatisflex.core.field.FieldQueryBuilder;
 import com.mybatisflex.core.mybatis.MappedStatementTypes;
 import com.mybatisflex.core.paginate.Page;
 import com.mybatisflex.core.provider.EntitySqlProvider;
-import com.mybatisflex.core.query.*;
+import com.mybatisflex.core.query.CPI;
+import com.mybatisflex.core.query.QueryColumn;
+import com.mybatisflex.core.query.QueryCondition;
+import com.mybatisflex.core.query.QueryWrapper;
 import com.mybatisflex.core.table.TableInfo;
 import com.mybatisflex.core.table.TableInfoFactory;
 import com.mybatisflex.core.util.*;
@@ -667,47 +670,39 @@ public interface BaseMapper<T> {
 
 
     default <R> Page<R> paginateAs(Page<R> page, QueryWrapper queryWrapper, Class<R> asType, Consumer<FieldQueryBuilder<R>>... consumers) {
-        List<QueryColumn> selectColumns = CPI.getSelectColumns(queryWrapper);
+        try {
-        List<QueryOrderBy> orderBys = CPI.getOrderBys(queryWrapper);
+            // 只有 totalRow 小于 0 的时候才会去查询总量
-        List<Join> joins = CPI.getJoins(queryWrapper);
+            // 这样方便用户做总数缓存，而非每次都要去查询总量
-        // 只有 totalRow 小于 0 的时候才会去查询总量
+            // 一般的分页场景中，只有第一页的时候有必要去查询总量，第二页以后是不需要的
-        // 这样方便用户做总数缓存，而非每次都要去查询总量
+            if (page.getTotalRow() < 0) {
-        // 一般的分页场景中，只有第一页的时候有必要去查询总量，第二页以后是不需要的
+                QueryWrapper countQueryWrapper = MapperUtil.optimizeCountQueryWrapper(queryWrapper);
-        if (page.getTotalRow() < 0) {
+                page.setTotalRow(selectCountByQuery(countQueryWrapper));
-            QueryWrapper countQueryWrapper = MapperUtil.optimizeCountQueryWrapper(queryWrapper);
+            }
-            long count = selectCountByQuery(countQueryWrapper);
+
-            page.setTotalRow(count);
+            if (page.isEmpty()) {
-        }
+                return page;
+            }
+
+            int offset = page.getPageSize() * (page.getPageNumber() - 1);
+            queryWrapper.limit(offset, page.getPageSize());
+
+            List<R> records;
+            if (asType != null) {
+                records = selectListByQueryAs(queryWrapper, asType);
+            } else {
+                records = (List<R>) selectListByQuery(queryWrapper);
+            }
+            MapperUtil.queryFields(this, records, consumers);
+            page.setRecords(records);
 
-        if (page.isEmpty()) {
             return page;
+
+        } finally {
+            // 将之前设置的 limit 清除掉
+            // 保险起见把重置代码放到 finally 代码块中
+            CPI.setLimitRows(queryWrapper, null);
+            CPI.setLimitOffset(queryWrapper, null);
         }
-
-        //重置 selectColumns
-        CPI.setSelectColumns(queryWrapper, selectColumns);
-        //重置 orderBys
-        CPI.setOrderBys(queryWrapper, orderBys);
-        //重置 join
-        CPI.setJoins(queryWrapper, joins);
-
-        int offset = page.getPageSize() * (page.getPageNumber() - 1);
-        queryWrapper.limit(offset, page.getPageSize());
-
-        if (asType != null) {
-            List<R> records = selectListByQueryAs(queryWrapper, asType);
-            MapperUtil.queryFields(this, records, consumers);
-            page.setRecords(records);
-        } else {
-            List<R> records = (List<R>) selectListByQuery(queryWrapper);
-            MapperUtil.queryFields(this, records, consumers);
-            page.setRecords(records);
-        }
-
-        // 将之前设置的 limit 清除掉
-        CPI.setLimitRows(queryWrapper, null);
-        CPI.setLimitOffset(queryWrapper, null);
-
-        return page;
     }
 
 

mybatis-flex-core/src/main/java/com/mybatisflex/core/row/RowMapper.java

@@ -19,7 +19,9 @@ import com.mybatisflex.core.FlexConsts;
 import com.mybatisflex.core.exception.FlexExceptions;
 import com.mybatisflex.core.paginate.Page;
 import com.mybatisflex.core.provider.RowSqlProvider;
-import com.mybatisflex.core.query.*;
+import com.mybatisflex.core.query.CPI;
+import com.mybatisflex.core.query.QueryColumn;
+import com.mybatisflex.core.query.QueryWrapper;
 import com.mybatisflex.core.util.CollectionUtil;
 import com.mybatisflex.core.util.MapperUtil;
 import com.mybatisflex.core.util.StringUtil;
@@ -431,47 +433,35 @@ public interface RowMapper {
      * @return
      */
     default Page<Row> paginate(String schema, String tableName, Page<Row> page, QueryWrapper queryWrapper) {
+        try {
+            CPI.setFromIfNecessary(queryWrapper, schema, tableName);
 
-        CPI.setFromIfNecessary(queryWrapper, schema, tableName);
+            // 只有 totalRow 小于 0 的时候才会去查询总量
+            // 这样方便用户做总数缓存，而非每次都要去查询总量
+            // 一般的分页场景中，只有第一页的时候有必要去查询总量，第二页以后是不需要的
+            if (page.getTotalRow() < 0) {
+                QueryWrapper countQueryWrapper = MapperUtil.optimizeCountQueryWrapper(queryWrapper);
+                page.setTotalRow(selectCountByQuery(schema, tableName, countQueryWrapper));
+            }
 
-        List<QueryColumn> selectColumns = CPI.getSelectColumns(queryWrapper);
+            if (page.isEmpty()) {
+                return page;
+            }
 
-        List<QueryOrderBy> orderBys = CPI.getOrderBys(queryWrapper);
+            int offset = page.getPageSize() * (page.getPageNumber() - 1);
+            queryWrapper.limit(offset, page.getPageSize());
 
-        List<Join> joins = CPI.getJoins(queryWrapper);
+            page.setRecords(selectListByQuery(schema, tableName, queryWrapper));
 
-        // 只有 totalRow 小于 0 的时候才会去查询总量
-        // 这样方便用户做总数缓存，而非每次都要去查询总量
-        // 一般的分页场景中，只有第一页的时候有必要去查询总量，第二页以后是不需要的
-        if (page.getTotalRow() < 0) {
-            QueryWrapper countQueryWrapper = MapperUtil.optimizeCountQueryWrapper(queryWrapper);
-            long count = selectCountByQuery(schema, tableName, countQueryWrapper);
-            page.setTotalRow(count);
-        }
-
-        if (page.isEmpty()) {
             return page;
+
+        } finally {
+            // 将之前设置的 limit 清除掉
+            // 保险起见把重置代码放到 finally 代码块中
+            CPI.setLimitRows(queryWrapper, null);
+            CPI.setLimitOffset(queryWrapper, null);
         }
 
-        //重置 selectColumns
-        CPI.setSelectColumns(queryWrapper, selectColumns);
-        //重置 orderBys
-        CPI.setOrderBys(queryWrapper, orderBys);
-        //重置 join
-        CPI.setJoins(queryWrapper, joins);
-
-        int offset = page.getPageSize() * (page.getPageNumber() - 1);
-        queryWrapper.limit(offset, page.getPageSize());
-
-        List<Row> records = selectListByQuery(schema, tableName, queryWrapper);
-        page.setRecords(records);
-
-        // 将之前设置的 limit 清除掉
-        CPI.setLimitRows(queryWrapper, null);
-        CPI.setLimitOffset(queryWrapper, null);
-
-        return page;
-
     }
 
 }

mybatis-flex-core/src/main/java/com/mybatisflex/core/util/MapperUtil.java

@@ -42,7 +42,7 @@ public class MapperUtil {
      *
      * <p><pre>
      * {@code
-     * SELECT COUNT(*) AS `total` FROM ( ...用户构建的 SQL 语句... );
+     * SELECT COUNT(*) AS `total` FROM ( ...用户构建的 SQL 语句... ) AS `t`;
      * }
      * </pre>
      *
@@ -58,22 +58,25 @@ public class MapperUtil {
      * 优化 COUNT 查询语句。
      */
     public static QueryWrapper optimizeCountQueryWrapper(QueryWrapper queryWrapper) {
-        List<QueryColumn> selectColumns = CPI.getSelectColumns(queryWrapper);
+        // 对克隆对象进行操作，不影响原来的 QueryWrapper 对象
-        List<QueryColumn> groupByColumns = CPI.getGroupByColumns(queryWrapper);
+        QueryWrapper clone = queryWrapper.clone();
+        // 将最后面的 order by 移除掉
+        CPI.setOrderBys(clone, null);
+        // 获取查询列和分组列，用于判断是否进行优化
+        List<QueryColumn> selectColumns = CPI.getSelectColumns(clone);
+        List<QueryColumn> groupByColumns = CPI.getGroupByColumns(clone);
         // 如果有 distinct 语句或者 group by 语句则不优化
         // 这种一旦优化了就会造成 count 语句查询出来的值不对
         if (hasDistinct(selectColumns) || hasGroupBy(groupByColumns)) {
-            return rawCountQueryWrapper(queryWrapper);
+            return rawCountQueryWrapper(clone);
         }
         // 判断能不能清除 join 语句
-        if (canClearJoins(queryWrapper)) {
+        if (canClearJoins(clone)) {
-            CPI.setJoins(queryWrapper, null);
+            CPI.setJoins(clone, null);
         }
-        // 最后将最后面的 order by 移除掉
+        // 将 select 里面的列换成 COUNT(*) AS `total`
-        // 将 select 里面的列换成 COUNT(*) AS `total` 就好了
+        CPI.setSelectColumns(clone, Collections.singletonList(count().as("total")));
-        CPI.setOrderBys(queryWrapper, null);
+        return clone;
-        CPI.setSelectColumns(queryWrapper, Collections.singletonList(count().as("total")));
-        return queryWrapper;
     }
 
     private static boolean hasDistinct(List<QueryColumn> selectColumns) {