ABAP Keyword Documentation → ABAP - Dictionary → ABAP CDS in ABAP Dictionary → ABAP CDS - Data Definitions → ABAP CDS - DDL for Data Definitions → ABAP CDS - DEFINE VIEW → ABAP CDS - SELECT → ABAP CDS - SELECT, ASSOCIATION
ABAP CDS - path_expr
Other versions:
7.31 | 7.40 | 7.54
Syntax
... [source.]_assoc1[
parameters][attributes]
[._assoc2[
parameters][
attributes] ... ] ...
Effect
Specifies an SQL path expression in a SELECT statement of a CDS view. A path expression of the CDS DDL is a string of CDS associations separated by periods (.) whose names are specified using _assoc1, _assoc2, and so on. The name of the CDS entity source in which the first CDS association is defined or published can be specified in front of this CDS association. The first CDS association of a path expression must be either:
- Defined in the current CDS view.
- Published as an element of the SELECT list or as an element list in a CDS view or CDS hierarchy that is a data source of the current view.
All further CDS associations must be published in the target data source of the directly prefixed CDS association in the path expression. No CDS associations can be used in a path expression that are defined in an abstract CDS entity.
attributes can be used to specify attributes in angle brackets after every CDS association. These attributes define the following further properties of this section of the path expression:
- Declaration of monovalency
- Type of the join expression defined when used
- Specified filter conditions
If the data source target of a specified CDS association is a CDS entity with input parameters, parameters must be used after the name _assoc to pass actual parameters to them. No parameters can be specified for a CDS association published as an element of a SELECT list.
Use of Path Expressions
Path expressions can be used as follows in the CDS DDL in ABAP CDS:
- Path expressions with CDS associations of any target data sources can publish their final CDS associations as elements of SELECT lists for use in other CDS entities or in ABAP SQL.
- Path expressions with CDS associations whose target data source is not an abstract CDS entity can be used as follows:
- To specify the target data source of the final CDS association as the data source data_source after FROM. The path expression represents an inner join (INNER JOIN) by default.
- To specify an appended element .element of the target data source of the last CDS association as an element of a SELECT list. The path expression represents a right outer join (LEFT OUTER JOIN) by default.
- To specify an appended element .element of the target data source of the last CDS association as an operand of WHERE or HAVING conditions, and WHEN conditions. The path expression represents a right outer join (LEFT OUTER JOIN) by default.
When a non-aggregated element of a SELECT list is specified with aggregate expressions and in a WHERE condition or HAVING condition, the result of the path expression must be monovalent. This means that the cardinality of all CDS associations used is either "to 1" or the path expression can contain only filter conditions that are declared as monovalent using the addition 1:.
The following is evaluated when a CDS entity is accessed using a path expression:
- The joins defined by the CDS associations, from left to right.
- All other conditions of the CDS entities in question.
The path expression addresses the full result of this evaluation or a single element appended using .element.
Notes
- The most simple path expression is the name of a single CDS association.
- When joins in path expressions are defined by CDS associations, note that their left side is always the CDS entity that publishes the CDS association. This applies particularly to CDS associations that are published in data sources of CDS entities and passed.
- CDS DDL path expressions can also be used in conditions in the ABAP CDS DCL of ABAP CDS.
- A CDS association whose target data source does not publish a CDS association cannot be followed by any further associations in a path expression. More specifically, no further CDS associations can be made into a path expression after CDS associations whose target data sources are database tables or classic views.
- When the CDS associations of the path expressions of a view are defined as joins, they are mapped to as few join expressions as possible. The ABAP annotation AbapCatalog.compiler.compareFilter is used as support here. The value true guarantees that CDS associations with semantically identical filter conditions do not produce differing join expressions.
- Path expressions with CDS associations whose target data source is an abstract CDS entity cannot be used anywhere where they could produce instances of join expressions.
Example
The following CDS view contains the simple path expression _scarr[inner].carrname in the SELECT list, whereby the attribute INNER is specified that controls the type of join. The program DEMO_FROM_JOIN_TO_ASSOCIATION demonstrates that this view returns the same result as a directly programmed inner join in ABAP CDS or in ABAP SQL.
@AccessControl.authorizationCheck: #NOT_REQUIRED
define view demo_cds_join2
as select from spfli
association to scarr as _scarr on
spfli.carrid = _scarr.carrid
{
_scarr[inner].carrname as carrier,
spfli.connid as flight,
spfli.cityfrom as departure,
spfli.cityto as arrival
}
Example
This example shows three CDS views, sales_order, business_partner, and invoice. The CDS view invoice uses its own CDS association and CDS associations from the other two views in path expressions:
- The CDS association sales_order of the CDS view business_partner is specified as a data source after FROM. A filter condition guarantees that only certain orders can be used as data sources.
- The separate CDS association invoice_header is used in a path expression as an operand in the WHERE condition.
- The CDS association note_header of the CDS view sales_order is addressed using the alternative name bpa in business_partner and defined as an element of the SELECT list. This means this CDS association can also be used in CDS views that use invoice as a data source.
define view sales_order as
select from snwd_so
association [0..1] to snwd_text_key as _note_header
on snwd_so.note_guid = _note_header.node_key
{ * } // Include all fields from snwd_text_key
define view business_partner as
select from snwd_bpa
association [0..*] to sales_order
on snwd_bpa.node_key = sales_order.buyer_guid
{ * }
define view invoice as
select from
/* Association "sales_order" with filter as data source */
business_partner.sales_order[
lifecycle_status <> 'C' and lifecycle_status <> 'X']
as bpa_so //alias for data source
/* Association only used in this view definition */
association [0..1] to snwd_so_inv_head as _invoice_header
on bpa_so.node_key = _invoice_header.so_guid
{ key bpa_so.node_key, //Field from ON-condition in _invoice_header
bpa_so.so_id,
bpa_so.note_guid, //Field from ON-condition in note_header
bpa_so.lifecycle_status,
/* Association is not published, but its element */
_invoice_header.dunning_level,
/* Association from data source is published here */
bpa_so.note_header }
/* Path expression in WHERE clause */
where _invoice_header.dunning_level > '0';
Executable Example
Path Expressions, Use in the SELECT List