ABAP CDs view with association example

1. ASSOCIATION Application scenarios of

• ASSOCIATION It's a kind of passing Join A join condition that gets data from multiple tables , But these are “ Connect on demand ”, in other words , They will only be triggered when the user accesses the required data that needs to be associated with the table
• because ASSOCIATION Is triggered on demand , When Join When there are more actual accesses, users only access a single or a few Join when , Compared with tradition, it can complete SQL
• ASSOCIATION Association cardinality of
  • [ 0 … 1 ] = At most one （at most one）
  • [ 1 … 1 ] = Only one-to-one correspondence is allowed （exactly one）
  • [ 0 … n ] = Associate any number （any number）
  • [ 1 … n ] = Associate at least one （at least one）
  • [ 1 … 1 ] [ 1 … n ] It ensures that the associated main table always has at least one record

2. Realization CDS VIEW WITH ASSOCIATION

• Create a CDS VIEW WITH ASSOCIATION
  
  

• Realization CDS VIEW WITH ASSOCIATION Code

  @AbapCatalog.sqlViewName: 'ZCDS_ASSO_01'
  @AbapCatalog.compiler.compareFilter: true
  @AbapCatalog.preserveKey: true
  @AccessControl.authorizationCheck: #CHECK
  @EndUserText.label: 'cds view with association'
  define view ZCDS_ASSOCIATIONS as select from spfli as t1
  association [1] to sflight as _sflight
      on $projection.carrid = _sflight.carrid 
  {
  key t1.carrid,
      t1.connid,
      t1.countryfr,
      t1.cityfrom,
      t1.airpfrom,
      t1.countryto,
      t1.cityto,
      t1.airpto,
      t1.fltime,
      t1.deptime,
      t1.arrtime,
      t1.distance,
      t1.distid,
      
      _sflight
  }
  

  

3. Data preview

• Right click anywhere , Click on Follow Association You can see ASSOCIATION
  

• double-click Associations see , This shows that the default Association The way is **[ 0 … 1 ]**
  

• Association _sflight
  

4. stay ABAP Call in

• frequently-used Select * Unable to get Association _sflight Data content in , This is the beginning of the story （Association It will only be triggered when the user accesses the required data of the associated table ）
  
• Correct reading method
  
• Activate error report ：The association “_SFLIGHT” could not be resolved. correct
  • Use incorrect call View Name An error will be reported during activation
    
  • resolvent ： Use View Name that will do