Query Object

编程语言可以包含sql语句，但许多开发者对此并不太熟悉。而且，你需要了解数据库设计方案以便形成查询。可以通过创建特殊的，隐藏的SQL内部参数化方法来避免这一点。但是这样难以构造更多的查询。而且，如果数据库设计方案改变，就会需要复制到SQL语句。

查询对象是一个解析器（interpreter）【Gang of Four】，也就是说，它是由多个对象组成的结构，该结构可以自身转化为一个sql查询。你可以通过引用类和域而不是表和列来创建这个查询。采用这种方式，那些编写查询的人就能够设计独立数据库方案的查询，并且数据库方案的变化也可以被封装到局部

《企业应用架构模式》 - Martin Fower

看到上面，我第一时间是想到Hibernate中的Criteria查询，他是Query Object很直观和跟经典的实现。但是就我个人使用来说，Criteria查询比较少，而且要记住几个英文很长的类，写出来巨繁琐（静态导入会好一些）。目前做项目都基于JPA的接口来开发。（但大多复杂查询还是使用原生sql查出来，然后自己转换对象！也有干脆使用mybatis）。就平时开发而言，简单快速好用的封装Query Object，然后配合链式编程（该实践中，良好的测试可以避免火车事故），使用起来是非常方便的。

查询对象可以很好的简单的完美的:^)跟 查询通道（QueryChannel）或者直接活动记录（ActiveRecord）+资源库（Repository）这些模式结合，形成简单好用的查询接口。

以下是我参考以前一些前辈，跟自己进行改进的一个Query Object实践，基本JPQL。 最终于我Repository 或DAO的查询接口可能是类似于这样的风格。

<T> T findEntity(Query q);
PageVo findPage(Query q);
List<T> findEntites(Query q);

然后这个Query的代码跟单元测试：

Query.java

package com.xz.marksix.repository;import java.util.ArrayList;
import java.util.List;import com.xz.marksix.infrastructure.AppContants;/*** <pre>* *  JPA 查询对象    * * @author XzhiF*             Sep 25, 2013* </pre>*/
public class Query
{private static final String SPACE = " ";private static final String SELECT = "SELECT";private static final String COUNT = "COUNT";private static final String FROM = "FROM";private static final String WHERE = "WHERE";private static final String AND = "AND";private static final String OR = "OR";private static final String ORDER_BY = "ORDER BY";private static final String ASC = "ASC";private static final String DESC = "DESC";private static final String JOIN = "JOIN";private static final String INNER_JOIN = "INNER JOIN";private static final String LEFT_JOIN = "LEFT JOIN";private static final String RIGHT_JOIN = "RIGHT JOIN";private static final String LEFT_OUTER_JOIN = "LEFT OUTER JOIN";private static final String RIGHT_OUT_JOIN = "RIGHT OUTER JOIN";private static final String LEFT_JOIN_FETCH = "LEFT JOIN FETCH";private static final String RIGHT_JOIN_FETCH = "RIGHT JOIN FETCH";private static final boolean ADD_PARAM = true;private static final boolean NOT_ADD_PARAM = false;private Class<?> entityClass;private String alias;private Integer pageNum;private Integer pageSize;private List<Object> paramters = new ArrayList<>();private StringBuilder selectClause = new StringBuilder();private StringBuilder fromClause = new StringBuilder();private StringBuilder joinClause = new StringBuilder();private StringBuilder whereClause = new StringBuilder();private StringBuilder orderByClause = new StringBuilder();private boolean fetchAllRecords = true;public Query( Class<?> entityClass, String alias ){this.entityClass = entityClass;this.alias = alias;/*** FROM abc.Def alais*/fromClause//.append( SPACE )//.append( FROM )//.append( SPACE )//.append( entityClass.getName() )//.append( SPACE )//.append( this.alias );}/*** evaluate 生成最后的JPQL语句*/public String evaluate(){StringBuilder result = new StringBuilder();/*** 以下构造要保持顺序，若重构时请注意*/evlauteAppendSelectClause( result );evlauteAppendFromClause( result );evlauteAppendJoinClause( result );evlauteAppendWhereClause( result );evlauteAppendOrderByClause( result );return result.toString().trim();}/*** evaluateCount 生成最后的查询总数的JPQL语句*/public String evaluateCount(){StringBuilder result = new StringBuilder();/*** 以下构造要保持顺序，若重构时请注意*/evlauteAppendSelectCountClause( result );evlauteAppendFromClause( result );evlauteAppendWhereClause( result );return result.toString().trim();}private void evlauteAppendSelectClause( StringBuilder result ){if ( isNotBlank( selectClause ) ){result.append( selectClause );}}private void evlauteAppendSelectCountClause( StringBuilder result ){result.append( SELECT )//.append( SPACE )//.append( COUNT )//.append( "(" )//.append( alias )//.append( ")" );}private void evlauteAppendFromClause( StringBuilder result ){result.append( fromClause );}private void evlauteAppendJoinClause( StringBuilder result ){if ( isNotBlank( joinClause ) ){result.append( joinClause );}}private void evlauteAppendWhereClause( StringBuilder result ){if ( isNotBlank( whereClause ) ){result.append( whereClause );}}private void evlauteAppendOrderByClause( StringBuilder result ){if ( isNotBlank( orderByClause ) ){result.append( orderByClause );}}/*** <pre>* 例如返回一个实体*    addSelectClause("e") "e" 跟new Query() 第二个别名参数要一至。* * 例如返回一个查询的VO对象*     addSelectClause("new VO(e.id,e.name)") "e" 跟new Query() 第二个别名参数要一至。* * 注意些方法只能调用一次，同一实例调用多次会抛出RepositoryException异常* </pre>* * @param expression JPQL片段* @return Query*/public Query addSelectClause( String expression ){checkSelectClauseIsBinded();selectClause.append( SELECT ).append( SPACE );if ( isBlank( expression ) ){selectClause.append( this.alias );}else{selectClause.append( expression );}return this;}private void checkSelectClauseIsBinded(){if ( isNotBlank( selectClause ) ){throw new RepositoryException( "selectClause已经绑定过不能再定绑定." );}}/*** <pre>*    结果将添加如  WHERE e.id=? AND e.name=? 的 JPQL片段*   例子:*    addWhereAndClause( id!=null, "e.id=?", id )* * </pre>* * @param canAdd 条件，如果成立 ，JPQL片段将被添加* @param expression JPQL片段* @param value 设置的值* @return Query*/public Query addWhereAndClause( boolean canAdd, String expression, Object value ){if ( canAdd ){return addWhereClause( AND, expression, value, ADD_PARAM );}return this;}public Query addWhereAndClause( boolean canAdd, String expression ){if ( canAdd ){return addWhereClause( AND, expression, null, NOT_ADD_PARAM );}return this;}/*** 直接添加JPQL片段* * @see Query#addWhereOrClause(boolean,*      String, Object)*/public Query addWhereAndClause( String expression, Object value ){return addWhereClause( AND, expression, value, ADD_PARAM );}/*** 直接添加JPQL片段不带有占位参数* * @see Query#addWhereOrClause(boolean,*      String, Object)*/public Query addWhereAndClause( String expression ){return addWhereClause( AND, expression, null, NOT_ADD_PARAM );}/*** <pre>*    结果将添加如  WHERE e.id=? OR e.name=? 的 JPQL片段*    例子:*    addWhereAndClause( id!=null, "e.id=?", id )* * </pre>* * @param canAdd 条件，如果成立 ，JPQL片段将被添加* @param expression JPQL片段* @param value 设置的值* @return Query*/public Query addWhereOrClause( boolean canAdd, String expression, Object value ){if ( canAdd ){return addWhereClause( OR, expression, value, ADD_PARAM );}return this;}public Query addWhereOrClause( boolean canAdd, String expression ){if ( canAdd ){return addWhereClause( OR, expression, null, NOT_ADD_PARAM );}return this;}/*** 直接添加JPQL片段* * @see Query#addWhereOrClause(boolean,*      String, Object)*/public Query addWhereOrClause( String expression, Object value ){return addWhereClause( OR, expression, value, ADD_PARAM );}/*** 直接添加JPQL片段， 不添加占位符号查询参数* * @see Query#addWhereOrClause(boolean,*      String, Object)*/public Query addWhereOrClause( String expression ){return addWhereClause( OR, expression, null, NOT_ADD_PARAM );}/*** addWhereClause*/private Query addWhereClause( String operation, String expression, Object value, boolean addParam ){prepareWhereClause( operation );whereClause.append( SPACE )//.append( expression.trim() );//if ( addParam ){paramters.add( value );}return this;}/*** <pre>* *   结果将添加如  ORDER BY e.id ASC, e.name ASC 的 JPQL片段*     例子:*    addOrderByAscClause( true, "e.id" )*  addOrderByAscClause( true, "e.name" )* </pre>* * @param canAdd 条件，如果成立 ，JPQL片段将被添加* @param expression JPQL片段* @return {@link Query}*/public Query addOrderByAscClause( boolean canAdd, String expression ){if ( canAdd ){return addOrderByAscClause( expression );}return this;}/*** 直接添加JPQL语句* * @see Query#addOrderByAscClause(boolean,*      String)*/public Query addOrderByAscClause( String expression ){return addOrderByClause( ASC, expression );}/*** <pre>* *  结果将添加如  ORDER BY e.id DESC, e.name DESC 的 JPQL片段*   例子:*    addOrderByAscClause( true, "e.id" )*  addOrderByAscClause( true, "e.name" )* </pre>* * @param canAdd 条件，如果成立 ，JPQL片段将被添加* @param expression JPQL片段* @return {@link Query}*/public Query addOrderByDescClause( boolean canAdd, String expression ){if ( canAdd ){return addOrderByClause( DESC, expression );}return this;}/*** 直接添加JPQL语句* * @see Query#addOrderByDescClause(boolean,*      String)*/public Query addOrderByDescClause( String expression ){return addOrderByClause( DESC, expression );}private Query addOrderByClause( String opration, String expression ){prepareOrderByClause();orderByClause.append( SPACE ).append( expression )//.append( SPACE )//.append( opration );return this;}/*** <pre>* * 添加JOIN语句，例如:*   .addJoinClause("d.sub s")  s为join的对象别名* * </pre>*/public Query addJoinClause( String expression ){return addCaseedJoinClause( JOIN, expression );}/*** <pre>* * 添加INNER JOIN语句，例如:*    .addInnerJoinClause("d.sub s")  s为join的对象别名* * </pre>*/public Query addInnerJoinClause( String expression ){return addCaseedJoinClause( INNER_JOIN, expression );}/*** <pre>* * 添加LEFT JOIN语句，例如:*     .addLeftJoinClause("d.sub s")  s为join对象后别名* * </pre>*/public Query addLeftJoinClause( String expression ){return addCaseedJoinClause( LEFT_JOIN, expression );}/*** <pre>* * 添加RIGHT JOIN语句，例如:*   .addRightJoinClause("d.sub s")  s为join的对象别名* * </pre>*/public Query addRightJoinClause( String expression ){return addCaseedJoinClause( RIGHT_JOIN, expression );}/*** <pre>* * 添加LEFT OUTER JOIN语句，例如:*   .addLeftOuterJoinClause("d.sub s")  s为join的对象别名* * </pre>*/public Query addLeftOuterJoinClause( String expression ){return addCaseedJoinClause( LEFT_OUTER_JOIN, expression );}/*** <pre>* * 添加RIGHT OUTER JOIN语句，例如:*     .addRightOuterJoinClause("d.sub s")  s为join的对象别名* * </pre>*/public Query addRightOuterJoinClause( String expression ){return addCaseedJoinClause( RIGHT_OUT_JOIN, expression );}/*** <pre>* 注意fetch也不应该与setMaxResults() 或 setFirstResult()共用，* 这是因为这些操作是基于结果集的，而在预先抓取集合类时可能包含重复的数据，也就是说无法预先知道精确的行数。* * 添加LEFT JOIN FETCH 语句，例如:*  .addLeftJoinFetchClause("d.sub s")  s为join的对象别名* * </pre>*/public Query addLeftJoinFetchClause( String expression ){return addCaseedJoinClause( LEFT_JOIN_FETCH, expression );}/*** <pre>* 注意fetch也不应该与setMaxResults() 或 setFirstResult()共用，* 这是因为这些操作是基于结果集的，而在预先抓取集合类时可能包含重复的数据，也就是说无法预先知道精确的行数。* * 添加LEFT JOIN FETCH 语句，例如:*   .addRightJoinFetchClause("d.sub s")  s为join的对象别名* * </pre>*/public Query addRightJoinFetchClause( String expression ){return addCaseedJoinClause( RIGHT_JOIN_FETCH, expression );}private Query addCaseedJoinClause( String whatJoin, String expression ){joinClause.append( SPACE ).append( whatJoin ).append( SPACE ).append( expression );return this;}private void prepareOrderByClause(){if ( isBlank( orderByClause ) ){orderByClause.append( SPACE ).append( ORDER_BY );}prepareOrderByClauseIfHasCondition();}private void prepareOrderByClauseIfHasCondition(){if ( orderByClause.length() != new String( SPACE + ORDER_BY ).length() ){orderByClause.append( "," );}}private void prepareWhereClause( String operation ){if ( isBlank( whereClause ) ){whereClause.append( SPACE ).append( WHERE );}prepareWhereClauseIfHasCondition( operation );}private void prepareWhereClauseIfHasCondition( String operation ){if ( whereClause.length() != new String( SPACE + WHERE ).length() ){whereClause.append( SPACE ).append( operation );}}private boolean isBlank( CharSequence c ){if ( c == null || c.length() == 0 ){return true;}return false;}private boolean isNotBlank( CharSequence c ){return !isBlank( c );}public Class<?> getEntityClass(){return entityClass;}public List<Object> getParameters(){return paramters;}/*** <pre>* * 设置该参数抓取数据库所有数据* 设置的分页数将无效，改方法不能与setPageNum 跟 setPageSize 同时使用* * 设置为true为全部抓取* 默认为false* * </pre>* * @param fetch 是否抓取全部数据* @return*/public Query setFetchAllRecords( boolean fetch ){this.fetchAllRecords = fetch;return this;}public boolean isFetchAllRecords(){return fetchAllRecords;}/*** - page*/public Query setPageNum( Integer pageNum ){this.fetchAllRecords = false;this.pageNum = pageNum;return this;}public Query setPageSize( int pageSize ){this.fetchAllRecords = false;this.pageSize = pageSize;return this;}public Integer getPageNum(){return ( pageNum == null || pageNum < 1 ) ? 1 : pageNum;}public Integer getPageSize(){return ( pageSize == null || pageSize < 1 ) ? AppContants.DEFAULT_PAGE_SIZE : pageSize;}public Integer getFirstResult(){return ( getPageNum() - 1 ) * getPageSize();}public Integer getMaxResults(){return getPageSize();}}

对应的单元测试代码：TestQuery.java

package com.xz.marksix.repository;import static org.junit.Assert.assertEquals;
import static org.junit.Assert.fail;import java.util.List;import org.junit.Test;/*** <pre>* *     测试Query生成jpql查询语子* * @author XzhiF*            Sep 25, 2013* </pre>*/
public class TestQuery
{private static final String ENTITY_NAME = Object.class.getName();@Testpublic void testMultiEvaluate() throws Exception{String expected = "FROM " + ENTITY_NAME + " d WHERE d.name=?";Query query = new Query( Object.class, "d" )//.addWhereAndClause( "d.name=?", "abc" );String result = query.evaluate();assertEquals( expected, result );/** second evaluate*/assertEquals( result, query.evaluate() );}@Testpublic void testAndOrWhereClause() throws Exception{String expected = "FROM " + ENTITY_NAME + " d WHERE d.name=? AND d.id=? OR d.id=? AND d.parent IS NULL";Query query = new Query( Object.class, "d" )//.addWhereAndClause( "d.name=?", "abc" )//.addWhereAndClause( "d.id=?", "abc" )//.addWhereOrClause( "d.id=?", "aa" )//.addWhereAndClause( "d.parent IS NULL" );String result = query.evaluate();assertEquals( expected, result );assertEquals( result, query.evaluate() );assertEquals( new Integer(3), new Integer(query.getParameters().size()) );}@Testpublic void testOrderByClause() throws Exception{String expected = "FROM " + ENTITY_NAME + " d WHERE d.name=? ORDER BY d.id DESC, d.name DESC, d.age ASC";Query query = new Query( Object.class, "d" )//.addWhereAndClause( "d.name=?", "abc" )//.addOrderByDescClause( "d.id" )//.addOrderByDescClause( "d.name" ).addOrderByAscClause( "d.age" );String result = query.evaluate();// System.out.println(result);assertEquals( expected, result );}@Testpublic void testJoinsClause() throws Exception{String expected = "FROM " + ENTITY_NAME + " d " + //"JOIN d.sub s" + //" INNER JOIN d.sub s" + //" LEFT JOIN d.sub s" + //" RIGHT JOIN d.sub s" + //" LEFT OUTER JOIN d.sub s" + //" RIGHT OUTER JOIN d.sub s" + //" LEFT JOIN FETCH d.sub s" + //" RIGHT JOIN FETCH d.sub s";Query query = new Query( Object.class, "d" )//.addJoinClause( "d.sub s" )//.addInnerJoinClause( "d.sub s" )//.addLeftJoinClause( "d.sub s" )//.addRightJoinClause( "d.sub s" )//.addLeftOuterJoinClause( "d.sub s" )//.addRightOuterJoinClause( "d.sub s" )//.addLeftJoinFetchClause( "d.sub s" )//.addRightJoinFetchClause( "d.sub s" );String result = query.evaluate();// System.out.println(result);assertEquals( expected, result );}@Testpublic void testClauseHasCondition() throws Exception{String expected = "FROM " + ENTITY_NAME + " d INNER JOIN d.sub s WHERE d.id=? OR d.name=? ORDER BY o.id ASC, o.name DESC";Query query = new Query( Object.class, "d" )//.addWhereAndClause( true, "d.id=?", "1" )//.addWhereAndClause( false, "d.id=?", "1" )//.addWhereOrClause( true, "d.name=?", "a" )//.addWhereOrClause( false, "d.name=?", "b" )//.addOrderByAscClause( true, "o.id" )//.addOrderByAscClause( false, "o.id" )//.addOrderByDescClause( true, "o.name" )//.addOrderByDescClause( false, "o.name" )//.addInnerJoinClause( "d.sub s" );String result = query.evaluate();// System.out.println(result);assertEquals( expected, result );}@Testpublic void testSelectClause() throws Exception{String expected = "SELECT d FROM " + ENTITY_NAME + " d";Query query = new Query( Object.class, "d" )//.addSelectClause( "d" );//String result = query.evaluate();// System.out.println(result);assertEquals( expected, result );expected = "SELECT new EntityVO(id,name) FROM " + ENTITY_NAME + " d";query = new Query( Object.class, "d" )//.addSelectClause( "new EntityVO(id,name)" );//result = query.evaluate();assertEquals( expected, result );}@Testpublic void testMultiAddSelectClause() throws Exception{Query query = new Query( Object.class, "d" )//.addSelectClause( "d" );try{query.addSelectClause( "a" );fail( "retry addSelectCluase should throw a exception" );}catch ( RepositoryException e ){}}@Testpublic void testWithinParams() throws Exception{Query query = new Query( Object.class, "d" )//.addWhereAndClause( "d.id=?", "1" )//.addWhereAndClause( "d.id=?", "2" )//.addWhereOrClause( "d.name=?", "a" )//.addWhereOrClause( "d.name=?", "b" );//List<Object> paramters = query.getParameters();assertEquals( "1", paramters.get( 0 ) );assertEquals( "2", paramters.get( 1 ) );assertEquals( "a", paramters.get( 2 ) );assertEquals( "b", paramters.get( 3 ) );}@Testpublic void testEvaluateCount() throws Exception{String expected = "SELECT COUNT(d) FROM " + ENTITY_NAME + " d WHERE d.id=? AND d.name=?";Query query = new Query( Object.class, "d" )//.addWhereAndClause( "d.id=?", "1" )//.addWhereAndClause( "d.name=?", "a" )//.addOrderByAscClause( "d.id" )//.addInnerJoinClause( "d.sub c" )//.addSelectClause( "d" );String result = query.evaluateCount();// System.out.println(result);assertEquals( expected, result );}}