Terry.Li-彬

準(zhǔn)備:

兩個(gè)表(實(shí)體), 1對(duì)多雙向關(guān)聯(lián):

班級(jí): Clazz (id, name)

學(xué)生: Student(id, name , class_id)

1. 查詢持久化對(duì)象  

1.1 簡(jiǎn)單查詢，返回?cái)?shù)據(jù)庫(kù)結(jié)構(gòu)

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1. sql = "select c.* from clazz c,student s where s.class_id = c.id";     
2.   
3. List<Clazz> clazzs = (List<Clazz>)session.createSQLQuery(sql).list();  

 sql = "select c.* from clazz c,student s where s.class_id = c.id";
List<Clazz> clazzs = (List<Clazz>)session.createSQLQuery(sql).list();

特別注意：返回結(jié)果是Object[]組成的List，通過(guò)Object下標(biāo)訪問(wèn)屬性

使用場(chǎng)合：非基于對(duì)象的查詢，復(fù)雜查詢

1.2 簡(jiǎn)單查詢，返回持久化對(duì)象

  sql = "select c.* from Clazz c , student s where s.class_id = c.id ";    List<Clazz> clazzs = (List<Clazz>) session.createSQLQuery(sql).addEntity(Clazz.class).list();

特別注意： 1.addEntity方法指定返回包含Clazz對(duì)象的List 2. 查詢出來(lái)的持久態(tài)對(duì)象，clazz對(duì)象的studets屬性是各代理對(duì)象，訪問(wèn)的時(shí)候才會(huì)去查詢DB 使用場(chǎng)合：基于對(duì)象的查詢，但對(duì)象簡(jiǎn)單查詢

1.3 多表查詢，返回多個(gè)實(shí)體

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1. String sql = "select {c.*}, {s.*} from Clazz c , student s where s.class_id = c.id   ";  
2.   
3. List<Clazz> clazzs = (List<Clazz>) session().createSQLQuery(sql)  
4.   
5.                                  .addEntity("c", Clazz.class)  
6.   
7.                                  .addEntity("s", Student.class).list();  

String sql = "select {c.*}, {s.*} from Clazz c , student s where s.class_id = c.id   ";
List<Clazz> clazzs = (List<Clazz>) session().createSQLQuery(sql)
.addEntity("c", Clazz.class)
.addEntity("s", Student.class).list();

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1. 特別注意：   
2. 1. addEntity方法指定了當(dāng)前返回實(shí)體的別名,而且在SQL語(yǔ)句里使用{c.*}這樣的語(yǔ)句,  
3. 它的意思是向別名為c的這個(gè)對(duì)象注入所有屬性值.  

特別注意：
1. addEntity方法指定了當(dāng)前返回實(shí)體的別名,而且在SQL語(yǔ)句里使用{c.*}這樣的語(yǔ)句,
它的意思是向別名為c的這個(gè)對(duì)象注入所有屬性值.

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1. 2. 這個(gè)查詢會(huì)返回一個(gè)Object的List,每個(gè)Object包含兩個(gè)對(duì)象一個(gè)Clazz,一個(gè)Student  

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1. 3. {}占位符里是對(duì)象的屬性,而非列名,如{s.class},而非{s.class_id}  

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1. 4. 必須注入對(duì)象的每個(gè)屬性值，你可以使用{c.*}，或者手工寫(xiě)全所有，但必須是所有屬性。（這個(gè)太讓我郁悶了。   

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1. 使用場(chǎng)合：基于對(duì)象的查詢，復(fù)雜查詢  

1.4  多表查詢，返回關(guān)聯(lián)實(shí)體

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1. String sql = "select {c.*}, {s.*} from Clazz c , student s where s.class_id = c.id   ";  
2.   
3. List<Clazz> clazzs = (List<Clazz>) session().createSQLQuery(sql)  
4.   
5.         .addEntity("c", Clazz.class)  
6.   
7.         .addJoin("s", "c.students").list();  

String sql = "select {c.*}, {s.*} from Clazz c , student s where s.class_id = c.id   ";
List<Clazz> clazzs = (List<Clazz>) session().createSQLQuery(sql)
.addEntity("c", Clazz.class)
.addJoin("s", "c.students").list();

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1. <p>特別注意: 這塊有些問(wèn)題，明明應(yīng)該返回Clazz的List的,但確返回包含Clazz和Student的Object的List, faint</p><p>使用場(chǎng)合：基于對(duì)象的查詢，復(fù)雜查詢</p>  

2. 查詢托管對(duì)象

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1. String sql = "select c.id, c.name from Clazz c , student s where s.class_id = c.id   ";     
2.   
3. List<Clazz> clazzs = (List<Clazz>) session.createSQLQuery(sql)        
4.   
5.                                      .addScalar("id", Hibernate.LONG)  
6.   
7.                                      .addScalar("name", Hibernate.STRING)       
8.   
9.                                      .setResultTransformer(Transformers.aliasToBean(Clazz.class)).list();  

String sql = "select c.id, c.name from Clazz c , student s where s.class_id = c.id   ";
List<Clazz> clazzs = (List<Clazz>) session.createSQLQuery(sql)
.addScalar("id", Hibernate.LONG)
.addScalar("name", Hibernate.STRING)
.setResultTransformer(Transformers.aliasToBean(Clazz.class)).list();

特別注意:

1. 如果不設(shè)置addScalar方法可能會(huì)報(bào)轉(zhuǎn)型錯(cuò)誤的異常.

2.托管查詢可以使用投影,只查詢指定的列屬性