One-to-many relationships can be captured using foreign keys?

[ZTY-star]

How are foreign keys defined in IDL? What does it do?

[vivekpandey02]

Hi ZTY-star,
You can not define the foreign keys in IDL files. But you can use the foreign key concepts in your applications.

[ZTY-star]

Hi ZTY-star,
You can not define the foreign keys in IDL files. But you can use the foreign key concepts in your applications.

Sorry, I do n’t understand. Can you give an example?

[vivekpandey02]

To understand relationship in DDS you need to understand following concepts:
Distributed Relational Information Modeling
– Topic Keys can be used to identify instances as well as relationships
– Relationships can be navigated by relying on a subset of SQL
– One-to-many relationships can be captured using foreign keys
– Many-to-many relationships need to be modeled using a topics
– Keys can be represented by an arbitrary number of Topic fields

Suppose you have 3 topics named Floor,Room and TempSensor. Topics types are given below:
Floor has a primary key fID. Room has a primary key rID and attribute fID is a foreign key. same in TempSensor, tID is a primary key and attribute rID acts as a foreign key.

struct Floor
{
short fID;
short level;
short open;
};
#pragma keylist Floor fID

struct Room
{
int rID;
float width;
float height;
float length;
short fId; // Foreign Key
};
#pragma keylist Room rID

struct TempSensor
{
short tID;
float temp;
float huminity;
int rID; // Foreign Key
};
#pragma keylist TempSensor tID

Now you need to maintain these relationship in your applications means you need to validate the received data as per the dependency and process accordingly.