Oracle中生成复杂结构的XML

在Oracle中,我们可以通过DBMS_XML包来将SQL语句查出的数据转成XML文件.但有时候我们需要的是复杂的多层结构的XML.

比较以下两个结构
A --- a1 ---
A --- a1 ---
A --- a1 ---
B --- b1 ---
B --- b1 ---
C --- c1 ---

A ---
  a1 ---
  a2 ---
  a3 ---
B ---
  b1 ---
  b2 ---
C ---
   c1 ---

对于第一种结构的XML,我们只需要简单的将A和a关联查询并生成XML即可
这里我要说明的是如何生成第二种结构的XML

实例场景:
表XML_PRIMARY
表XML_SECONDARY
两个表有外键的关联,Primary是主表,Secondary是Primary的从表

create table XML_PRIMARY
(
  P_ID   NUMBER not null,
  P_NAME VARCHAR2(20)
);
alter table XML_PRIMARY
  add constraint PK_XML_PRIMARY primary key (P_ID)
  using index;
create table XML_SECONDARY
(
  S_ID   NUMBER not null,
  S_NAME VARCHAR2(10),
  P_ID   NUMBER
);
alter table XML_SECONDARY
  add constraint PK_XML_SECONDARY primary key (S_ID)
  using index;
alter table XML_SECONDARY
  add constraint FK_XML_PRIM_SECO foreign key (P_ID)
  references XML_PRIMARY (P_ID);

问题: 如何将从表的数据以独立的结构生成XML显示出来
解决办法: 将从表的数据以数据集合的形式查询出来

1. 建立与从表同构的对象类型
CREATE OR REPLACE TYPE Typ_o_Xml_Secondary AS OBJECT
(
  s_Id   NUMBER,
  s_Name VARCHAR2(10),
  p_Id   NUMBER
)
2. 建立从表的表类型
CREATE OR REPLACE TYPE TYP_XML_SECONDARY AS TABLE OF TYP_O_XML_SECONDARY
3. 建立带从表数据集合的主表类型
CREATE OR REPLACE TYPE Typ_o_Xml_Primary AS OBJECT
(
  p_Id   NUMBER,
  p_Name VARCHAR2(20),
  s_Data Typ_Xml_Secondary
)
4. 利用Cast和Multiset将子查询转化为子结果集
SELECT Typ_o_Xml_Primary(p_Id,
                         p_Name,
                         CAST(MULTISET (SELECT s_Id, s_Name, p_Id
                                 FROM Xml_Secondary
                                WHERE p_Id = Xml_Primary.p_Id) AS
                              Typ_Xml_Secondary)) AS Xml_Primary
  FROM Xml_Primary
5. 将SQL转化为XML
CREATE OR REPLACE PROCEDURE Prc_Xml_Subxml AS
  Qryctx Dbms_Xmlgen.Ctxhandle;
  RESULT CLOB;
BEGIN
  Qryctx := Dbms_Xmlgen.Newcontext('
                  SELECT Typ_o_Xml_Primary(p_Id,
                         p_Name,
                         CAST(MULTISET (SELECT s_Id, s_Name, p_Id
                                 FROM Xml_Secondary
                                WHERE p_Id = Xml_Primary.p_Id) AS
                              Typ_Xml_Secondary)) AS Xml_Primary
                    FROM Xml_Primary
            ');
  RESULT := Dbms_Xmlgen.Getxml(Qryctx);
  Dbms_Output.Put_Line(RESULT);
END Prc_Xml_Subxml;

输出的结果实例:
<?xml version="1.0"?>
<ROWSET>
 <ROW>
  <XML_PRIMARY>
   <P_ID>1</P_ID>
   <P_NAME>Primary data 1</P_NAME>
   <S_DATA>
    <TYP_O_XML_SECONDARY>
     <S_ID>11</S_ID>
     <S_NAME>Sec 11</S_NAME>
     <P_ID>1</P_ID>
    </TYP_O_XML_SECONDARY>
    <TYP_O_XML_SECONDARY>
     <S_ID>12</S_ID>
     <S_NAME>Sec 12</S_NAME>
     <P_ID>1</P_ID>
    </TYP_O_XML_SECONDARY>
    <TYP_O_XML_SECONDARY>
     <S_ID>13</S_ID>
     <S_NAME>Sec 13</S_NAME>
     <P_ID>1</P_ID>
    </TYP_O_XML_SECONDARY>
   </S_DATA>
  </XML_PRIMARY>
 </ROW>
 <ROW>
  <XML_PRIMARY>
   <P_ID>2</P_ID>
   <P_NAME>Primary data 2</P_NAME>
   <S_DATA>
    <TYP_O_XML_SECONDARY>
     <S_ID>21</S_ID>
     <S_NAME>Sec 21</S_NAME>
     <P_ID>2</P_ID>
    </TYP_O_XML_SECONDARY>
    <TYP_O_XML_SECONDARY>
     <S_ID>22</S_ID>
     <S_NAME>Sec 22</S_NAME>
     <P_ID>2</P_ID>
    </TYP_O_XML_SECONDARY>
   </S_DATA>
  </XML_PRIMARY>
 </ROW>
 <ROW>
  <XML_PRIMARY>
   <P_ID>3</P_ID>
   <P_NAME>Primary data 3</P_NAME>
   <S_DATA>
    <TYP_O_XML_SECONDARY>
     <S_ID>31</S_ID>
     <S_NAME>Sec 31</S_NAME>
     <P_ID>3</P_ID>
    </TYP_O_XML_SECONDARY>
   </S_DATA>
  </XML_PRIMARY>
 </ROW>
</ROWSET>

后续研究:
1. 其实,如果只是要数据的话,没有必要用Typ_o_Xml_Primary类型再做一次格式化,如下语句即可达到目的
SELECT p_Id,
       p_Name,
       CAST(MULTISET (SELECT s_Id, s_Name, p_Id
               FROM Xml_Secondary
              WHERE p_Id = Xml_Primary.p_Id) AS Typ_Xml_Secondary)
  FROM Xml_Primary
但,结果会让XML中的<S_DATA>标签变成<CAST(MULTISET (SEL........>,所以这里我用了一个结构来生成标签的名字.
或者
SELECT p_Id,
       p_Name,
       CAST(MULTISET (SELECT s_Id, s_Name, p_Id
               FROM Xml_Secondary
              WHERE p_Id = Xml_Primary.p_Id) AS Typ_Xml_Secondary) as XXX
  FROM Xml_Primary
也可以去掉类似于<CAST(MULTISET (SEL........>的标签名,但就无法命名XML最外层的标签.
总之,仁者见仁,智者见智吧 :)

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