dbms_lob包功能强大,简单应用。既可以用来读取内部的lob对象,也可以用来处理bfile对象。但处理两者之间,还有一点差别。处理内部lob对象(blob,clob)时,可以进行读和写,但处理外部lob对象bfile时,只能进行读操作,写的操作可以用pl/sql处理。另外用sql也可以处理lob,但要注意sql仅可以处理整个lob,不能操作lob的数据片。
在dbms_lob包中内建了read(),append,write(),erase(),copy(),getlength(),substr()等函数,可以很方便地操作lob对象。这里不做深入讨论,读者可以参看相关的书籍。
对于pl/sql,下面介绍一种技巧,用动态的pl/sql语句处理clob对象来传替表名! example 1.
动态PL/SQL,对CLOB字段操作可传递表名table_name,表的唯一标志字段名field_id,clob字段名field_name记录号v_id,开始处理字符的位置v_pos,传入的字符串变量v_clob
修改CLOB的PL/SQL过程:updateclob
create or replace procedure updateclob(
table_name in varchar2,
field_id in varchar2,
field_name in varchar2,v_id in number,
v_pos in number,
v_clob in varchar2)
is
lobloc clob;
c_clob varchar2(32767);
amt binary_integer;
pos binary_integer;
query_str varchar2(1000);
begin
pos:=v_pos*32766 1;
amt := length(v_clob);
c_clob:=v_clob;
query_str :='select '||field_name||'from '||table_name||'
where '||field_id||'= :id for update ';
--initialize buffer with data to be inserted or updated
EXECUTE IMMEDIATE query_str INTO lobloc USING v_id;
--from pos position, write 32766 varchar2 into lobloc
dbms_lob
.write(lobloc, amt, pos, c_clob);
commit;
exception
when others then
rollback;
end;
create or replace function getclob(
table_name in varchar2,
field_id in varchar2,
field_name in varchar2,
v_id in number,
v_pos in number) return varchar2
is
lobloc clob;
buffer varchar2(32767);
amount number := 2000;
offset number := 1;
query_str varchar2(1000);
begin
query_str :='select '||field_name||' from '||table_name||'
where '||field_id||'= :id ';
--initialize buffer with data to be found
EXECUTE IMMEDIATE query_str INTO lobloc USING v_id;
offset:=offset (v_pos-1)*2000;
--read 2000 varchar2 from the buffer
dbms_lob
.read(lobloc,amount,offset,buffer);
return buffer;
exception
when no_data_found then
return buffer;
end; 用法说明:
用select getclob(table_name,field_id,field_name,v_id,v_pos) as partstr from dual;
可以从CLOB字段中取2000个字符到partstr中,编一个循环可以把partstr组合成dbms_lob.getlength(field_name)长度的目标字符串。
二、对于在其他不同的开发环境,例如vc,vb,pb,java等环境下对lob的处理,处理方法不尽相同,在这里将简要举几个例子来说明不在oracle开发环境下对lob的处理。
(一) 在pb中的处理
exampler 2.
string ls_path,ls_filename,ls_jhdh
long ll_num,ll_count,rtn
blob ole_blob
ll_num=dw_lb.getrow()
if ll_num>0 then ls_jhdh=dw_lb.object.ct_njhdh[ll_num]
select count(*) into :ll_count from sj_jh_jhfjb where
ct_jhdlxbh='1' and ct_jhdh=:ls_jhdh and ct_jdlxbh=:is_jdlx;
if ll_count>0 then
rtn=messagebox("提示","是否要修改此附件",question!,yesno!,1)
if rtn=1 then
SELECTBLOB ct_jhfjnr INTO le_blob from sj_jh_jhfjb where
ct_jhdlxbh='1' and ct_jhdh=:ls_jhdh and ct_jdlxbh=:is_jdlx;
ole_1.objectdata =ole_blob
If ole_1.activate(offsite!) <> 0 Then
Messagebox("OLE Activate","不能激活")
Return -1
end If
end if
else
messagebox("提示","没有附件")
end if
end if
Option Explicit
Dim rn As ADODB.Connection
Public Function CreateDataSource(DataSource As String, UserID
As String, Password As String) As Boolean
On Error GoTo DbConErr:
Set rn = New ADODB.Connection
With rn
.ConnectionString = "Provider=OraOledb.Oracle.1;"