本文阐述了ABAP CDS association的概念,并且展示了在CDS视图中和SQL语句中写路径表达式(Path Expression)代码的方法。我也会解释如何在CDS asociation中指定inner join——默认情况下是left outer join,以及如何为association添加过滤。
对于CDS的相关开发,SAP希望我们使用association而不是join,因为association更加接近“概念思维”。基本上,association本身不是join,它只是有关join连接可能性的元数据,它会按需成为join。真实的join会在路径表达式使用association的时候被创建。
一个简单的CDS association例子,它看起来和left outer join没区别:
@AbapCatalog.sqlViewName: ‘ZCDS_ASSOC11‘ define view zcds_assoc1 as select from scarr as sca association [0..1] to spfli as _spfli on sca.carrid = _spfli.carrid { * }
暴露CDS association的例子:
@AbapCatalog.sqlViewName: ‘ZCDS_ASSOC41‘ @AccessControl.authorizationCheck: #NOT_REQUIRED define view zcds_assoc4 as select from sairport as sair association [1..*] to spfli as _spfli on $projection.airportfrom = _spfli.airpfrom { sair.id as airportfrom, sair.name, sair.time_zone, -- exposing association _spfli }
在下面的例子里,你可以看到SPFLI表对SFLIGHT表和SAIRPORT表的association。通过别名alias _sfli和SFLIGHT和_sair,SAIRPORT的全部字段暴露在projection列表中。当路径表达式用于调用association时,会根据选择字段创建join条件:spfli.carrid = sflight.carrid and spfli.connid = sflight.connid and on spfli.airport = sairport.id。
@AbapCatalog.sqlViewName: ‘ZCDS_ASSOC21‘ @AccessControl.authorizationCheck: #NOT_REQUIRED define view zcds_assoc2 as select from spfli association to sflight as _sfli on spfli.carrid = _sfli.carrid and spfli.connid = _sfli.connid association [1..1] to sairport as _sair on $projection.airportfrom = _sair.id { spfli.carrid, spfli.connid, spfli.airpfrom as airportfrom, -- exposing association _sfli, _sair }
在下面的例子里,定义association时使用了上面的CDS entity,ZCDS_ASSOC2 :
@AbapCatalog.sqlViewName: ‘ZCDS_ASSOC31‘ @AccessControl.authorizationCheck: #NOT_REQUIRED define view zcds_assoc3 as select from scarr association [1..1] to zcds_assoc2 as _cdsassoc on $projection.carrierid = _cdsassoc.carrid { scarr.carrid as carrierid, -- Exposing Association _cdsassoc }
Open SQL语句中的路径表达式:在SQL语句中调用CDS association,需要使用如下的路径表达式。在上面的CDS association中,通过_cdsassoc暴露了完整的projection列表。
DATA(w_dbfeature) = cl_abap_dbfeatures=>use_features( requested_features = VALUE #( ( cl_abap_dbfeatures=>views_with_parameters ) ) ). IF w_dbfeature IS NOT INITIAL. SELECT carrierid , \_cdsassoc\_sfli-fldate AS flightdate, \_cdsassoc\_sair-name AS flightname FROM zcds_assoc3 WHERE carrierid = @carrid INTO TABLE @DATA(t_data1). ENDIF.
CDS视图中的路径表达式:
@AbapCatalog.sqlViewName: ‘ZCDS_ON_ASSOC1‘ define view zcds_on_assoc with parameters airport: S_FROMAIRP as select from zcds_assoc2 as cds2 { cds2.carrid, cds2.connid, cds2.airportfrom, cds2._sair.name, -- use inner join...by default association uses left outer join cds2._sfli.planetype } where cds2.airportfrom = :airport
如我所提到的那样,在被路径表达式调用时,CDS association会默认创建left outer join。
在SPFLI表数据中,没有RTM机场的航班。
当我们输入参数airport = RTM的时候 ,下面的CDS视图的查询结果会是一条RTM机场的数据,但是这条记录里没有carrid。
@AbapCatalog.sqlViewName: ‘ZCDS_ON_ASSOC41‘ define view zcds_on_assoc4 with parameters airport: S_FROMAIRP as select from zcds_assoc4 as cds_assoc { cds_assoc.airportfrom, cds_assoc.name, cds_assoc.time_zone, cds_assoc._spfli.carrid -- use inner join...by default association uses left outer join } where cds_assoc.airportfrom = :airport
运行上面的CDS视图:
data preview中的结果:
为了把默认的left outer join变成inner join,我们需要使用[inner],如下:
@AbapCatalog.sqlViewName: ‘ZCDS_ON_ASSOC41‘ define view zcds_on_assoc4 with parameters airport: S_FROMAIRP as select from zcds_assoc4 as cds_assoc { cds_assoc.airportfrom, cds_assoc.name, cds_assoc.time_zone, cds_assoc._spfli[inner].carrid -- use inner join...by default association uses left outer join } where cds_assoc.airportfrom = :airport
如果运行它,输入参数RTM,得到的结果为空:
目前,还不可以在CDS association中使用right outer join。
CDS association中的过滤例子如下:
@AbapCatalog.sqlViewName: ‘ZCDS_ASSOC_FILT‘ define view ZCDS_ASSOC_FILTER as select from zcds_assoc2 as cds2 { cds2._sair[ id = ‘TYO‘ ].name, cds2._sfli.planetype }
CDS视图的输出结果:
希望本文对你有帮助!
本文链接:https://www.cnblogs.com/hhelibeb/p/9202781.html
英文原文:CDS Associations and 路径表达式s – ABAP on HANA
原文地址:https://www.cnblogs.com/hhelibeb/p/9202781.html