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ABAP CDs table function introduction and examples

2022-07-28 01:16:00 【51CTO】

Reference blog ：

《ABAP CDS Table Function Introduction and examples 》

ABAP CDS Table Function

stay ABAP CDS Table Function In the development process , We will use the field structure 、 Parameters （ Optional ）、association Equal pass class / Methods are defined as entities . adopt AMDP We can go straight to ABAP Layer write stored procedure , And encapsulate it in classes / In the method , For more information, see the previous article ：ABAP Medium AMDP（ABAP-Managed Database Procedures .

scene

Each airline provides flight connections to different cities in the world , Users want to see all cities supported by a particular airline in a single field , The content is separated by commas . Because the number of cities of each airline is different , We need a logic to connect cities , No matter how many pieces of data there are in the query results .

In the regular ABAP CDS We can use CONCAT function , But when using it , We need to define a fixed number of fields , since CDS The view cannot implement the processing dynamic logic required here , How to deal with it ？

This is a use of ABAP CDS Table Function A great scene , Because we can use simple database functions STRING_AGG（String Aggregation）. This function is SQL Script Available in the , But it is still not supported ABAP CDS View .

Development

ABAP CDS Table Function Introduction and examples _sql

Edit the generated entity , Contains the following ：

Field :

Client
Airline Code
Airline Name
Cities To

class : ZCL_FLIGHTS_DEMO_CDS
Method : FLIGHTS_CONNECTIONS

The result should be ：

       
       define table function ZDEMO_FLIGHTS_TABLE_FUNCTIONreturns{client       : abap.clnt;airline_code : s_carr_id;airline_name : s_carrname;cities_to    : abap.string;}implemented by methodZCL_FLIGHTS_DEMO_CDS=>FLIGHTS_CONNECTIONS;
      
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Of course , Now? ZCL_FLIGHTS_DEMO_CDS There is no such thing as . next step , Let's create it ：

ABAP CDS Table Function Introduction and examples _ stored procedure _02

Let class contain IF_AMDP_MARKER_HDB Interface . This step will take you ABAP Class to AMDP class , And it allows you to write stored procedures inside the methods of classes .

       
       PUBLIC SECTION.
       
INTERFACES if_amdp_marker_hdb.
      
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In the method implementation, we need to introduce some configuration options ：

BY DATABASE FUNCTION: Will mark the method as table function, Another option is through BY DATABASE PROCEDURE Mark as stored procedure .
FOR HDB: Set the database type to HDB (HANA database ).
LANGUAGE SQLSCRIPT: HANA Language of database storage .
OPTIONS READ-ONLY: Data modification is not allowed in stored procedures .
USING: Definition table function Database tables consumed in 、 Views or stored procedures . In this case , Only visit SFLIGHTS View .

       
       METHOD flights_connections BY DATABASE FUNCTIONFOR HDBLANGUAGE SQLSCRIPTOPTIONS READ-ONLYUSING sflights.
       
<< Your code >>
       
ENDMETHOD.
      
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Let's prepare two of the query segmentation logic SELECT sentence .

first SLECT Need to get Client, Airline Code, Airline Name and City To Field , And pass DISTINCT Keyword de duplication , Because we will find the city records of the same airline on different connection dates ,

AMDP One of the advantages of is that you can SELECT The query results of are transmitted to “ Internal table ”, And can execute new SELECT To read its data . Let's apply the benefits of this feature , And will be the first SELECT The query result of the statement is named itab_cities.

       
       itab_cities =SELECT DISTINCTas client,asasasFROM
      
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In the second SELECT in , We need to itab_cities Read data in and implement database methods STRING_AGG To gather multiple cities and airlines . In order to achieve this function, we need to be based on Client,Airline Code and Name Field GROUP BY entry . It's written in ：

       
       RETURNSELECT client,             airline_code,             airline_name,', ' ORDER BY city_to) asFROMGROUP BY client,                airline_code,                airline_name;
      
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Be careful ：table function There should always be return parameters , So remember in the last SELECT Put a RETURN sentence . in addition , Notice that we convert the field name to the previous ABAP CDS Table Function Declared field name , If you don't provide a suitable alias , When activated, the compiler will give a prompt .

class ZCL_FLIGHTS_DEMO_CDS The final version of is like this ：

       
       CLASS zcl_flights_demo_cds DEFINITION  PUBLIC  FINALCREATE PUBLIC
       
PUBLIC    INTERFACES if_amdp_marker_hdb.
       
CLASS-METHODS:FOR TABLE FUNCTION
       
  PROTECTED SECTION.PRIVATEENDCLASS.
       
CLASS
       
  METHOD flights_connectionsBY DATABASE FUNCTIONFORLANGUAGEREAD-ONLYUSING
       
    itab_cities =SELECT DISTINCTas client,asasasFROM
       
    RETURNSELECT client,             airline_code,             airline_name,', ' ORDER BY city_to) asFROMGROUP BY client,                airline_code,                airline_name;
       
  ENDMETHOD.
       
ENDCLASS.
      
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