Association modeling method in SAP segw transaction code

Association Models are used to describe OData Different in the model Entity Type The relationship between .

Let's take a concrete example ：

Principal Entity( The main body )： representative association Leading end of .

Cardinality( base )： Specify the relationship between the principal entity type and the dependent entity type . Press F4 Or click to select .

The multiplicity of associations is as follows :

• 0: 0 . .1: There is only one instance , It is also allowed to 0.
• 1: One-to-one relationship . Only one is allowed at any time association example .
• N: 1 . . n： One-to-many relation . One or more instances can appear .
• M：0 . .n： Zero to multiple relationships . There can be zero or more instances .

For reference constraints (referential constraints) Specify the following parameters , The purpose is to set each key of the entity type , An attribute associated with a dependent entity type :

• Body key (Principal key)： Press F4 Select a key attribute in the entity type .
• Dependency property (Dependent property)： Press F4 Select the attribute that specifies the dependent entity type .

Referential Constraints An example of ：

Reference constraints (Referential Constraints) Can be used to specify 1:1 or 1:n Associated foreign key relationships .

Association Set Group a series of related instances , Be similar to Entity Set Grouping entity type instances . therefore , It depends on the respective entity types associated with the underlying , Specify the relationship between two entity sets .

Suppose there is one based on entity type Author and Book Of 1:n association Author_To_Books, There may be one Association Set WrittenBy, be used for Entity Set Authors and Books, And the other one Association Set FictionWrittenBy, be used for Entity Set FictionAuthors and FictionBooks.

It means , If you follow Authors Feed Navigation links for items , It will generate Books Feed, And follow FictionAuthors Feed Links to items , Will generate FictionBooks summary .

Although both Structurally equal , Because they are based on the same entity type , But it has different semantics , And may contain a different number of entries .