CDS view是SAP目前推出的下一代database views，SAP認為傳統(tǒng)的database view只是將多張表進行關聯(lián)，CDS View是一個成熟的Data Model，它有很多SE11中所沒有的新特性，并且可以被SAP產(chǎn)品外的Application使用。

1 在Eclipse中創(chuàng)建CDS View

右擊新建ABAP Object，選擇CSD->Data Definition

2 CDS View代碼

2.1 Define View / Define View with Join

使用模板生成的代碼如下

@AbapCatalog.sqlViewName: 'ZV_MONSTERS'
@AbapCatalog.compiler.compareFilter: true
@AccessControl.authorizationCheck: #CHECK
@EndUserText.label: 'Monster CDS views'
define view zcds_monsters as select from ztmonster_header as
monster_header
inner join ztmonster_items as monster_items
    on monster_header.db_key = monster_items.db_key
left outer join ztmonster_pets as monster_pets
    on monster_header.monster_number = monster_pets.owner
{
    key monster_header.monster_number as monster_number ,
    monster_header.name as monster_name ,
    LPAD ( monster_header.tax_number, 10 , '0' ) as hat_size ,
    SUBSTRING ( monster_header.name, 1 , 1 ) as first_initial ,
    case monster_header.evilness
        when 'BANKER_STYLE_EVIL' then 'REALLY SCARY'
        when 'EVIL' then
            case monster_header.strength
                when 'REALLY STRONG ' then 'SCARY'
                else ' NOT SO SCARY REALLY '
                end
        when 'SLIGHTLY_EVIL' then 'SLIGHTLY SCARY '
        else 'NOT REALLY SCARY AT ALL '
    end as scariness
}
where monster_header.sanity < 10
    and monster_header.color = 'GREEN'

以@開頭的為注解，除了默認的注解，可以自己添加比如buffer的注解，按F1可以獲得注解的介紹

@AbapCatalog.buffering.status : #ACTIVE
@AbapCatalog.buffering.type : #SINGLE

CSD veiw中，可以使用 inner jion / left jion等join命令，相比ABAP定義更廣泛了，通過as添加別名，使得看起來更具有實際意義。CDS中訪問表的字段使用點號.而不是傳統(tǒng)ABAP中的波浪號~。在SE11中我們定義字段時，左邊是human-friendly names, 比如CUSTOMER / CUSTOMER_NAME，而右邊是 data element ,比如 KUNNR and NAME1，CDS 中只定義human-friendly names，其類型有所取出的數(shù)據(jù)庫表字段類型自動定義。這有點類似于ABAP中通過DATA( )來定義數(shù)據(jù)的結構。所有的字段都放在{}中，在select jion關鍵詞后，在where關鍵詞前。上面例子中，通過LPAD可以將tax_number的值比如3補全成0000000003，通過SUBSTRING來取首字母。字段定義還可以用case語句。最后跟where條件語句，cds中可以用IS NULL / IS NOT NULL來判斷是否為空。
激活后，在se11中可以查看view

2.2 Define View with Association

SAP希望大家更多的是用association而不是jion，這更體現(xiàn)了概念思維，assocation不僅僅是jion，它是數(shù)據(jù)字典存儲的一種可能的jion連接的metadata，實際的jion在association被使用時才創(chuàng)建。
兩張表通過外鍵鏈接對我們來說很容易理解，但這其實與實際不匹配，比如我們下3個不同類型訂單時，我們對header數(shù)據(jù)和item數(shù)據(jù)并沒有有意思地去區(qū)別，因為通常概念中，很明顯一個訂單要有item數(shù)據(jù)，否則是沒有意義的。再比如通過表LFA1/LFM1尋找supplier的purchasing related data，通過association，我們可以用Supplier.PurchasingData.BlockingFlag 而不是LFM1 ~ SPERM 。當你創(chuàng)建了association view連接起address和customer，就可以在order item的customer中重用這個association view。
Association View定義如下，monster可能沒有pets，也可能有多個，因此設為[0..*]，header和item的關系可以設成[1..*]，如果jion兩個主鍵字段，可以用[1..1]。另外，SAP推薦assocation的名字前面加下劃線來區(qū)分CDS view中標準字段。

@AbapCatalog.sqlViewName: 'zv_monsters_ass'
@AbapCatalog.compiler.compareFilter: true
@AccessControl.authorizationCheck: #CHECK
@EndUserText.label: 'Monsters CDS View with Association'
define view Zcds_Monsters_Association as select from ztmonster_header as monster
association [0..*] to ztmonster_pets as _Pet
    on monster.monster_number = _Pet.owner {
    
    key monster.monster_number as MonsterNumber ,
    key _Pet.pet_number as PetNumber ,
    _Pet.owner as Owner ,
    monster.name as OwnerName ,
    _Pet.pet_name as Name ,
    _Pet.pet_type as Type,
    _Pet.pet_species as Species,
    _Pet // Make association public
}

2.3 Define View with Parameters

前面建立的CDS view，其中where條件是hard-code的，我們希望能通過參數(shù)來指定where條件，比如傳統(tǒng)ABAP中

SELECT * FROM zv_monster_pars
    WHERE color EQ p_color
    AND sanity IN s_sanity .

可以通過如下代碼定義參數(shù)，參數(shù)后面是其data element。

@AbapCatalog.sqlViewName: 'zv_monsters_pars'
@AbapCatalog.compiler.compareFilter: true
@AccessControl.authorizationCheck: #CHECK
@EndUserText.label: 'Monster CDS View with Parameters'
define view Zcds_Monsters_Parameters
    with parameters p_sanity_low : ZDE_MONSTER_SANITY ,
                    p_sanity_high: ZDE_MONSTER_SANITY ,
                    p_color : ZDE_MONSTER_COLOR
as select from ztmonster_header as monster {
    key monster.monster_number as MonsterNumber,
    monster.name as name ,
    monster.color as color ,
    monster.sanity as sanity ,
    monster.strength as strength
}
  where monster.color = :p_color and
     sanity between :p_sanity_low and :p_sanity_high

在程序中可以通過如下代碼來調(diào)用

SELECT * FROM zcds_monsters_parameters(
    p_color = @p_color ,
    p_sanity_low = @s_sanity- l ow,
    p_sanity_high = @s_sanity-high )
INTO TABLE @DATA(colorful _mad_monster_tablel)
WHERE strength~ 'REALLY_STRONG '.

2.4 Extend View

在SE11中，我們通過append對table或view進行增強，在CDSview中，對原有的CDS View進行增強可以如下

@AbapCatalog.sqlViewAppendName: 'ZV_MONSTERS_EXT'
@EndUserText.label: 'Monster CDS view extension'
extend view ZCDS_MONSTERS with ZCDS_MONSTERS_EXTENSION {
    monster_header.age,
    monster_header.monster_count as counts
}

增強后，原CDS View將有增強標記

在原始view中，可以看到append的字段

2.5 Table Function

定義table function如下，table function必須將clinet作為參數(shù)傳入，returns中的字段即為返回的字段，取數(shù)邏輯放在AMDP Class的方法中。

@EndUserText.label: 'Table Function'
define table function ZCDS_tablefun
with parameters @Environment.systemField: #CLIENT
                clnt : abap.clnt
returns {
  client : s_mandt;
  carrname : s_carrname;
  connid : s_conn_id;
  city_from : s_from_cit;
  city_to : s_to_city;
}
implemented by method ZLL_DEMO_AMDP_FUNCTIONS=>GET_flights;

定義AMDP class，繼承接口if_amdp_marker_hdb，

CLASS zll_demo_amdp_functions DEFINITION
  PUBLIC
  FINAL
  CREATE PUBLIC .

  PUBLIC SECTION.

    INTERFACES if_amdp_marker_hdb .
    CLASS-METHODS get_flights FOR TABLE FUNCTION zcds_tablefun .

  PROTECTED SECTION.
  PRIVATE SECTION.

ENDCLASS.


CLASS zll_demo_amdp_functions IMPLEMENTATION.

  METHOD get_flights
         BY DATABASE FUNCTION FOR HDB
         LANGUAGE SQLSCRIPT
         OPTIONS READ-ONLY
         USING scarr spfli.
    RETURN SELECT sc.mandt as client, sc.carrname, sp.connid, sp.cityfrom, sp.cityto
                  from scarr as sc
                    inner join spfli as sp on sc.mandt = sp.mandt and
                                              sc.carrid = sp.carrid
                    ORDER BY sc.carrname, sp.connid;

  endmethod.
ENDCLASS.

2.6 Authority Checks

在DDL中，我們配置@AccessControl.authorizationCheck: #CHECK，一個完整的CDS View需要 DDL + DCL

@EndUserText.label: 'Authority Check for CDS view' 
@MappingRole: true 
define role Zdcl_Monsters_Parameters { 
    grant 
        select 
            on 
                Zcds_Monsters_Parameters 
                    where 
                      //  condition; 
                      // -- Example WHERE condition 
                      // -- Two-field mapping to PFCG authorization with filter on read authorization
                       ( color ) = aspect pfcg_auth( z_mon_col, color, ACTVT = '03' ) ;
                      // and 
                      // -- Equals-or-initial operator 
                      // ( CustomerCountry ) ?= aspect pfcg_auth( S_ACM_DEMO, SACMCNTRY ) 
                      // or 
                      // -- Reference to the logged on users name 
                      // CreatedBy = aspect User 
                      // or 
                      // -- Literal condition 
                      // isPublic = 'X'; 
 
}