CDS Hierarchies, RESTful ABAP Programming Model

In this blog post, I am going to talk about a new way of creating CDS Hierarchies. Earlier before 1809 (On-Premise release) or 1811(Cloud Release), there was a different way to create CDS Hierarchies.

Also, I will demonstrate a step-by-step tutorial to create a simple basic CDS Hierarchy. To make it really relevant for everyone I will start by creating TABLES, then to CDS Views, and then CDS Hierarchy.

Before jumping into Tutorial lets see the Introduction of this CDS Hierarchy.

CDS Hierarchies

CDS Hierarchy is a new way to define Hierarchy, it is written using Data Definition Language.

Syntax starts with DEFINE HIERARCHY

Basic Syntax rule of CDS Hierarchy follows

[@entity_annot1]
[@entity_annot2]
...
[@hierarchy_annot1]
[@hierarchy_annot2]
...
[DEFINE] HIERARCHY cds_entity
         [parameter_list]
         AS PARENT CHILD HIERARCHY(
           SOURCE cds_view
           CHILD TO PARENT ASSOCIATION _hierarchy_assoc
           [DIRECTORY _directory_assoc FILTER BY cond_expr]
           START WHERE cond_expr
           SIBLINGS ORDER BY field1 [ASCENDING|DESCENDING][,
                             field2 [ASCENDING|DESCENDING], ...]
           [DEPTH depth]
           [NODETYPE node_type]
           [MULTIPLE PARENTS {NOT ALLOWED}|LEAVES|ALLOWED]
           [ORPHANS ERROR|IGNORE|ROOT]
           [CYCLES ERROR|BREAKUP]
           [GENERATE SPANTREE] )
     { element_list }

◈ Here First thing is to define CDS entity name for Hierarchy.

DEFINE HIERARCHY ztest_hierarchy

◈ Now if there are any input parameters required then mention below this in the parameter list.
NOTE: As of now, only PARENT-CHILD HIERARCHY is supported.

◈ After this, you need to mention SOURCE VIEW.

NOTE: Here a CDS view should be used which has self-association between Parent and Child and that association should be exposed in that CDS (see example below).

◈ Now mention the exposed association name in CHILD TO PARENT ASSOCIATION _exposedAssc
◈ Now the user has an option to put DIRECTORY syntax with directory association and filtered by condition expressions. This will filter out the following rows which are not satisfying the condition expression

Example of this:

CDS View

@AbapCatalog.sqlViewName: 'DEMOPACHSRCDIR'
@AccessControl.authorizationCheck: #NOT_REQUIRED
define view DEMO_CDS_PARENT_CHILD_SRC_DIR
  as select from
    demo_parchld_dir
    association [1..*] to DEMO_CDS_PARENT_CHILD_SRC_DIR as _pcr on
      $projection.parent = _pcr.id and
      $projection.dir_entry =  _pcr.id
    association [1..*] to demo_hiera_dir                as _dir   on
      $projection.dir_entry = _dir.dir_entry
    {
      _pcr,
      _dir,
      id,
      parent_id as parent,
      dir_entry
    }

CDS Hierarchy

define hierarchy DEMO_CDS_PARENT_CHILD_DIR
  with parameters
    p_id1 : abap.char(2),
    p_id2 : abap.char(2),
    p_dir : abap.char(2)
      as parent child hierarchy(
    source
      DEMO_CDS_PARENT_CHILD_SRC_DIR
      child to parent association _pcr
      directory _dir filter by dir_entry = :p_dir
      start where
        id = :p_id1 or id = :p_id2
      siblings order by
        parent
      multiple parents allowed
    )
    {
      id,
      parent,
      dir_entry
    }

• Now comes START WHERE with condition expression, where a user can put from where hierarchy should begin
• After this user can sort the Hierarchy w.r.t to its SIBLINGS with the statement – SIBLINGS ORDER BY
• Now comes some optional syntaxes:
• DEPTH – used to define hierarchy till which level, you can use parameter also in this.
• NODETYPE – its defines element of the Hierarchy as node type, which is used on consuming this Hierarchy
• MULTIPLE PARENTS – This can have three values ALLOWED, LEAVES ONLY and NOT ALLOWED which is self-understandable
• ORPHANS – If the Source view has some orphan nodes then it has three options – ERROR or IGNORE or ASSIGN to ROOT NODES
• CYCLES – This is used to check if there is any cycle created, if a user is mentioning this then MULTIPLE PARENTS ALLOWED need to be put.
• GENERATE SPAN TREE is still not supported.

Now, let’s move to the tutorial to have a basic understanding of this.

Create an ABAP table

From the Context menu of an ABAP system select TABLE and click on the Database table to create table

1. Enter the package – in my case, I used Local Package

2. Enter table name – Z**_HIER_TBL

3. Enter Description – Parent-Child Hierarchy table

Now add the fields:

◈ id – Data Type (char10)

◈ parentId – Data Type (char10)

◈ Name – Data Type (char50)

Now let’s write a report program to insert values in this table

From the context menu select others ABAP object and then search for Program

Now add values to the table

Now execute the report to insert values in the table.

After executing to report go to the table and press F8 to see that values are inserted in the table

Create a CDS View

Now after creating a table and inserting values into it, let’s create CDS view

Open the context menu and search for Data Definition

Add below code to CDS. Here we are creating self association with Parent Id.

@AbapCatalog.sqlViewName: 'ZYV_HIER'

@AbapCatalog.compiler.compareFilter: true

@AbapCatalog.preserveKey: true

@AccessControl.authorizationCheck: #CHECK

@EndUserText.label: 'CDS Hierarchy view for Parent Child Hier'

define view ZYV_PARENT_CHILD_HIER as select from zyv_hier_tbl

    association[1..1] to ZYV_PARENT_CHILD_HIER as _child on

    $projection.parentId = _child.id

    {

    _child,

    id,

    parentid as parent,

    name 

}

Note: Exposing of association is important here as it will be used in creating Hierarchy

Create CDS Hierarchy

Now its time to create CDS Hierarchy on top of this CDS View. Again open the context menu and search for Data Definition

Now paste below code to create Hierarchy.

define hierarchy ZYV_HIERARCHY

  as parent child hierarchy(

    source ZYV_PARENT_CHILD_HIER

    child to parent association _child

    start where

      id = '1'

    siblings order by

      id ascending

  )

{

  id,

  parent,

  $node.hierarchy_rank        as h_rank,

  $node.hierarchy_tree_size   as h_tree_size,

  $node.hierarchy_parent_rank as h_parent_rank,

  $node.hierarchy_level       as h_level,

  $node.hierarchy_is_cycle    as h_is_cycle,

  $node.hierarchy_is_orphan   as h_is_orphan,

  $node.node_id               as h_node_id,

  $node.parent_id             as h_parent_id

}

Here we have:

◈ Source as the CDS View we created before this step.

◈ We have access to $node where we get all the values regarding hierarchy

◈ In place of Start where –  Id as 1 we can put a parameter which is then passed from outside