Abap 扩展CD视图失败

我有两个CD视图，ztest_CD和ztex_CD，其中

ztest_CD

是一个普通视图，

ztex_CD

是一个扩展

ztest_CD

的视图

在

ztex\u cds

中，我关联了另一个表。当我激活

ztest\u CD

时，我收到 此错误消息：

表名\u book未知或被别名遮挡

当我双击时，

ztex\u CD

出现在前面，当我单击“激活”时，它以

NO

错误和警告结束

ztest_CD代码：

@AbapCatalog.sqlViewName: 'zt_cds'
@AbapCatalog.compiler.compareFilter: true
@AbapCatalog.preserveKey: true
@AccessControl.authorizationCheck: #CHECK
@EndUserText.label: 'test cds'
define view ztest_cds as select from sflight 
association [1..1] to spfli 
 on sflight.carrid = spfli.carrid
 and sflight.connid = spfli.connid{
key carrid,
key connid,
key fldate,
price,
currency
} 

@AbapCatalog.sqlViewAppendName: 'ztextend_cds'
@EndUserText.label: 'test extend cds'
extend view ztest_cds
with ztex_cds 
association to sbook as _book
        on _book.carrid = sflight.carrid
        and _book.connid = sflight.connid
association [1..1] to scustom as _cust
on _cust.id = _book.customid{
_book.bookid,
_book.customid,
 _cust.id,
_cust.name,
_cust.form,
_cust.street
}   

ztex_CD代码：

@AbapCatalog.sqlViewName: 'zt_cds'
@AbapCatalog.compiler.compareFilter: true
@AbapCatalog.preserveKey: true
@AccessControl.authorizationCheck: #CHECK
@EndUserText.label: 'test cds'
define view ztest_cds as select from sflight 
association [1..1] to spfli 
 on sflight.carrid = spfli.carrid
 and sflight.connid = spfli.connid{
key carrid,
key connid,
key fldate,
price,
currency
} 

@AbapCatalog.sqlViewAppendName: 'ztextend_cds'
@EndUserText.label: 'test extend cds'
extend view ztest_cds
with ztex_cds 
association to sbook as _book
        on _book.carrid = sflight.carrid
        and _book.connid = sflight.connid
association [1..1] to scustom as _cust
on _cust.id = _book.customid{
_book.bookid,
_book.customid,
 _cust.id,
_cust.name,
_cust.form,
_cust.street
}   

---

我应该如何激活

ztest\u CD

呢？那么问题是什么？在ztex\u CD中，我关联了另一个表。激活ztest\u CD时，我会收到以下错误消息：表名\u book未知或被别名隐藏。我应该如何激活ztest\u CD？