Navigation property and entityset usage in SAP segw transaction code

Entity types include one or more navigation attributes . Navigation attributes describe the navigation path between entity relationships .

It is an attribute of an entity , Represents a link from this entity to one or more related entities .

The navigation attribute is bound to the association type (association type), Allow from one end of the entity type that declares the navigation attribute ( Data source for navigation ) Navigate to the relevant end at the other end .

Navigation attributes are created through association Necessary for linking from one entity to another .

Before creating navigation properties , You need to create entity types and associations first (association).

The navigation properties folder appears only after adding entity types .

double-click SEGW Inside Navigation Properties Folder , open mass edit view, I can see every one of them navigation property The following five columns need to be maintained ：

stay Service Builder Entity sets are used in projects to combine instances of entity types with instances of any type derived from this particular entity type .

Entity type (Entity Type) Describe the data structure , The entity set contains instances of a given structure (instance).

Right click “ Data model ” Folder , choice “ establish ”, And then choose “ Entity set ”. in addition , When you right-click the entity set folder and select Create , You can create a new entity set . open “ Create entity set ” Dialog box .

As shown in the figure below ：

Requires filter checkbox The meaning of ： Selecting this check box means that the service implementation needs a filter (filter). If you select this check box , You cannot directly access the entity set , And not without $filter In the case of expression, query the entity set .

Association

Association describes the relationship between two or more entities , This relationship has an explicit name .

Associations define peer-to-peer relationships between participating entity types , Different... Can be supported at both ends multiplicities, such as 1 For more than , How to 1,N:M wait .

An example of correlation is Customer and Order Relationship between entities , As shown in the figure below ：