TYPES - association
7.31 | 7.40 | 7.54
... ASSOCIATION _assoc TO node ON tcomp1 = scomp1
[AND tcomp2 = scomp2
[AND ... ]]
[USING KEY key_name] ...
Defines a mesh association named
_assoc for a mesh node of a mesh type. The
TYPES can only be used
in the definition of a mesh type between TYPES
BEGIN OF MESH and TYPES END
OF MESH. The mesh node for which a mesh association is defined is its start node. The mesh
node specified after
TO is the target node.
Any node in the current mesh (including the start node) can be specified as the target node
node. A mesh association with the same source and target node is a
self association (also known as a reflexive association).
The name of a mesh association cannot be longer than 30 characters. It can only contain the letters A-Z, the digits 0-9, and the underscore "_" character, and cannot begin with a digit.
- The mesh associations defined for a mesh node are evaluated in expressions and statements for meshes in mesh paths.
- It is not mandatory to define a target node before the start node to make the target node visible. However, the Code Completion function of the editor only works properly if the target node is defined before the start node.
_is recommended as the naming convention for mesh associations. The name that follows this prefix should contain the target node name (in non-reflexive mesh associations). This convention makes it easier to read the mesh path.
... ON tcomp1 = scomp1 [AND tcomp2 = scomp2 [AND ... ]]
For every mesh association, a condition must be specified after
ON that consists of at least one
comparison for equality.
Additional comparisons for equality can be added using
AND. The left operand
tcomp of every comparison must be a directly specified column of the target
node. The right operand
scomp must be a directly specified column of the start node and this column must be compatible with the column of the target node.
A mesh association represents the relationship between the start node and target node. It assigns all the rows of the target node that meet the condition to a row of the start node.
The mesh associations are type-only attributes and therefore affect the compatibility of mesh types. Mesh associations are evaluated in mesh paths in expressions and in statements for meshes.
ONcondition, the target node components are on the left and the start node components are on the right. This is the same as in other statements and expressions for internal tables, where the columns of the table to be searched are always specified on the left.
As a general rule, the target node components specified on the left of an
ONcondition should be key fields of the table key used for the condition. This ensures the best possible system performance when accessing data.
... USING KEY key_name
Using the addition
USING KEY, a table key of the target node can be specified
ON condition of a mesh association. The target node is the one used in expressions and statements to evaluate
meshes for accessing the mesh node:
- A secondary key using its name
The primary key using its predefined name
primary_keyor using an alias. If the primary key is specified, the target node must be a sorted table or a hashed table.
The name of the table key must be specified directly. In other words, it cannot be specified dynamically
in a data object. If the table key is specified explicitly, the
ON condition must be defined to allow optimal key access.
If a sorted key or the primary key is specified, the conditions specified after
ONmust cover an initial left part of the key fields in the target table.
If a secondary hash key or a primary key of a hashed table is specified, the conditions specified after
ONmust cover all key fields in the target table.
If the addition
USING KEY is not specified, the primary key is used to access the mesh node, which means that access is not always optimal.
When the mesh association is used in a mesh path, the table
key specified in the definition of the
ON condition can be overridden by specifying
USING KEY in an
additional condition. In this case, the
ON condition and the additional condition are combined to make one single condition, which must meet the above prerequisites.
Declares a mesh type. Some of the internal tables used have secondary keys used with
USING in the definitions of the mesh associations.
TYPES: t_scarr TYPE HASHED TABLE OF scarr WITH UNIQUE KEY carrid, t_spfli TYPE HASHED TABLE OF spfli WITH UNIQUE KEY carrid connid WITH NON-UNIQUE SORTED KEY carrid COMPONENTS carrid, t_sflight TYPE HASHED TABLE OF sflight WITH UNIQUE KEY carrid connid fldate WITH NON-UNIQUE SORTED KEY carrid_connid COMPONENTS carrid connid, t_sairport TYPE HASHED TABLE OF sairport WITH UNIQUE KEY id, BEGIN OF MESH t_flights, scarr TYPE t_scarr ASSOCIATION _spfli TO spfli ON carrid = carrid USING KEY carrid, spfli TYPE t_spfli ASSOCIATION _sflight TO sflight ON carrid = carrid AND connid = connid USING KEY carrid_connid ASSOCIATION _sairport TO sairport ON id = airpfrom, sflight TYPE t_sflight, sairport TYPE t_sairport, END OF MESH t_flights.