Contents:

1. CDS entities
2. CDS associations (“normal”, compositions, and to-parent)
3. Clauses
4. Operands and expressions
   1. Operands
      1. Typed literal
      2. Untyped literal
      3. Field
      4. Parameter
      5. Session variable
   2. Expressions
      1. Arithmetic expression
      2. Aggregate function
      3. Case distinction (simple and complex)
      4. Cast expression (including new casts since release 7.55)
      5. Reusing expressions from the SELECT list with $projection 
      6. Relational operators
      7. Path expressions
      8. Amounts and quantities in expressions
   3. Built-in functions
      1. Numeric functions
      2. String functions
      3. Coalesce function
      4. Conversion functions (type conversion, unit and currency conversion, date and time conversion)
5. CDS system entities
6. CDS tuning objects
7. CDS entity extensions
8. Development pipeline

1. CDS entities

The following CDS entities are available in release ABAP Platform 2022 for data modeling.

Did you know?

• Check our Data Source Matrix to learn how to combine data sources in CDS: Data sources after FROM and association targets.
• CDS entities are like chameleons: even after you’ve activated and transported an entity, you can change the type of your CDS entity. For example, you have a CDS view and want to convert it into a custom entity for specialization. Or you want to convert an abstract entity into a view to have more options. As long as the consumers are not affected, just change the syntax and activate and transport the changed object.

2. CDS associations

Associations describe the relationships between CDS entities. They define a join that is instantiated only when fields are retrieved from the associated entity.

Use cases of CDS associations and how they are transformed into joins are documented here. Moreover, there’s a blog post: From Open SQL Joins to CDS Associations | SAP Blogs.

Types of associations:

“Normal”, not specialized CDS association

• Available since 7.4 SP5.
• Available in CDS view entities, CDS projection views, CDS custom entities, CDS abstract entities, and CDS DDIC-based views.
• Docu
• Syntax:

ASSOCIATION [ [min..max] ] TO target [AS _assoc] ON cds_cond 
  [ WITH DEFAULT FILTER cds_cond ]

CDS composition

• Specialized CDS association that defines the current entity as parent and the composition target as child.
• Available since ABAP 7.75, OP 1809 SP01.
• Available in CDS view entities, CDS projection views, CDS custom entities, CDS abstract entities, and CDS DDIC-based views.
• Docu
• Syntax:

COMPOSITION [ [min..max] ] OF target [AS _compos]

Association to parent

• Specialized CDS association that defines the current entity as child and the association target as parent. The child depends on the parent and cannot exist without the parent. For example, a sales order item (composition child) always belongs to a sales order header (composition parent).
• Available since ABAP 7.75, OP 1809 SP01.
• Available in CDS view entities, CDS projection views, CDS custom entities, CDS abstract entities, and CDS DDIC-based views.
• Docu
• Syntax:

ASSOCIATION TO PARENT target [AS _assoc] ON $projection.cds_cond

3. Clauses

4. Operands and expressions

4.1 Operands

4.2 Expressions

Arithmetic expressions

• Available since 7.4 SP5
• Docu

Aggregate functions

• Available since 7.4 SP5
• Docu

Case distinction

• Simple case is available since 7.4 SP5
• Searched case is available since 7.4 SP8
• New in release 7.89 | 7.57 | 2208: THEN ELSE NULL is available to explicitly define the null value as return value if no matches are found.
• Docu

A case expression in ABAP CDS always returns exactly one value, depending on the conditions. The simple case expression compares an expression to several other expressions for equality:

CASE operand 
           WHEN operand1 THEN result1 
          [WHEN operand2 THEN result2] 
           ... 
          [{ELSE resultn | ELSE NULL}] 
      END

The complex case expression (aka ‘searched case’) evaluates N independent conditions. The first case to be evaluated to TRUE returns the result. If none of the conditions are true, the result is determined by the ELSE branch:

CASE WHEN cds_cond1 THEN result1 
        [WHEN cds_cond2 THEN result2] 
        [WHEN cds_cond3 THEN result3] 
          ... 
        [{ELSE resultn | ELSE NULL}] 
    END

Cast expression

• Data type conversion
• Available since 7.4 SP5, but the cast matrix has been extended over time.
• Docu (including full cast matrix)
• Syntax:

• CAST( <expression> AS <datatype> [PRESERVING TYPE])

• New casts since release 7.55

• FROM	TO
  SSTRING	DEC, CURR, QUAN, INT1, INT2, INT4, INT8, DECFLOAT16, and DECFLOAT34
  CHAR	DEC, CURR, QUAN, INT1, INT2, INT4, INT8, DECFLOAT16, and DECFLOAT34
  DATS	DEC, CURR, QUAN, INT1, INT2, INT4, INT8, DECFLOAT16, and DECFLOAT34
  TIMS	DEC, CURR, QUAN, INT1, INT2, INT4, INT8, DECFLOAT16, and DECFLOAT34
  DECFLOAT16	CHAR
  DECFLOAT34	CHAR
  FLTP	DEC, CURR, QUAN, INT1, INT2, INT4, INT8, DECFLOAT16, and DECFLOAT34

Reusing expressions from the SELECT list

• $projection.elementName reuses an expression from the SELECT list in another operand position of the same CDS entity. This enables further processing of calculated fields and avoids the workaround of building a view stack for that purpose.
• Available since 7.56 | 7.84 | 2105
• Docu
• Example:

• define view entity DEMO_CDS_EXPRESSION_REUSE 
    as select from demo_expressions 
  { 
        //arithmetic expression 
        abap.decfloat34'123.45E6'              as arith, 
        $projection.arith * 2                  as arith_reuse, 
  
        //cast expression 
        cast(char1 as abap.numc(10))           as cast1, 
        coalesce($projection.cast1, numc2)     as cast_reuse, 
  
        //built-in function 
        abs(dec1)                              as builtIn, 
        cast($projection.builtIn as abap.int4) as builtIn_reuse, 
  }
  

Relational operators

Path expressions

Path expressions can be used to include fields from associated sources in the field list of the CDS entity. A path expression can also go over several levels. It is also possible to add attributes to the evaluation of the associations, for example to filter or to define the join type.

Example:

_Items[1:currency <> 'EUR'].material = 'WOOD' 

Amounts and quantities in expressions

Amount and quantity handling in expressions in ABAP CDS has been overhauled since release 7.56 | 7.84 | 2105. See the following blog post for details: ABAP CDS Cheat Sheet: Amounts and Quantities in ABAP CDS | SAP Blogs.

4.3 Built-in functions

Numeric functions 

• Docu

String functions

• Docu

Coalesce function

The coalesce function checks for null values.

Syntax:

COALESCE( arg1, arg2 )

 case cast( _a.char1 as char3)
          when substring( cast( 'AA' as char2), $parameters.p1, 2*2)  then 'text1'
          when case 'a' when 'b' then 'c' end                         then 'text2'
          else NULL
          end                 as CaseExp

5. CDS system entities

• CDS system entities are CDS entities delivered with an ABAP Platform that implement basic functionality, similar to ABAP system classes.
• Can be used as data source in other CDS entities or in ABAP SQL.
• Available since 7.56 | 7.84 | 2105
• Docu

System entity	Description
SERIES_GENERATE_DATE	CDS table function that creates a table with a series of dates.
SERIES_GENERATE_INTEGER	CDS table function that creates a table with a series of numbers.
SERIES_GENERATE_TIME	CDS table function that creates a table with a series of times.
SERIES_GENERATE_TIMESTAMP	CDS table function that creates a table with a series of time stamps.

Example: Creating a series of dates using the CDS system entity SERIES_GENERATE_DATE:

FINAL(current_date) = sy-datum.
FINAL(one_year_later) = current_date + 365.

SELECT * FROM series_generate_date( step       = 30,
                                    from_value = @current_date,
                                    to_value   = @one_year_later )
  ORDER BY element_number
  INTO TABLE @FINAL(date_series_gen).

cl_demo_output=>display( date_series_gen ).

Returns a series of dates:

6. CDS tuning objects

• A CDS tuning object is a CDS object defined with CDS DDL in ADT that defines technical properties of a CDS entity.
• Currently, there is only one type of CDS tuning object available: the CDS entity buffer.
• A CDS entity buffer is defined using DEFINE ENTITY BUFFER ON.
• Available since 7.57 | 7.87 | 2202
• Docu
• Buffering CDS View Entities | SAP Blogs

7. CDS entity extensions

Statement	Can be used for	Available since
EXTEND VIEW ENTITY	CDS view entity CDS projection view	7.87 | 1911 | 7.55
EXTEND CUSTOM ENTITY	CDS custom entity	7.89 | 2208 | 7.57
EXTEND ABSTRACT ENTITY	CDS abstract entity	7.84 | 2105 | 7.56
EXTEND VIEW	CDS DDIC-based view	7.40, SP08

8. Development pipeline

What can you expect to see in future releases? The following features appeared in my crystal ball. But hey: no guarantee, no legal claims to be made:

• CDS simple types: Self-defined data types that might be simple or structured and can be used wherever a built-in type can be used. Similar to data elements or structures in ABAP Dictionary. Syntax: DEFINE TYPE.
• CDS scalar functions: Self-defined functions. Similar to ABAP-Managed Database Procedures (AMDP) but can be specified directly in a CDS view and can be used in different runtimes. Syntax: DEFINE SCALAR FUNCTION.
• CDS aspects: Reusable artifacts in CDS. CDS aspects allow decomposing entity definitions into parts with different lifecycles, in this way enabling separation of concerns. The approach is borrowed from disciplines like aspect-oriented programming.

ABAP CDS celebrates its 10th anniversary this year. In September 2012, the ABAP CDS workstream was set up, and that’s how it all started rolling. What is your experience with ABAP CDS? Has it made development easier? Are you missing any features? Do you need more rollout or support? Feel free to use the Comments section below to share your personal experiences with ABAP Core Data Services.