SAP Persistence - Creating Source Code Automatically

Editor's Notes

• #7: So, now let’s take a look at some of the key components of the Persistence Service. The SAP Persistence Service consists of global classes and interfaces. The upper four interfaces, that you see here outlined in red, are shared between all Persistent Classes. The lower three classes, outlined in red, are specific, and automatically generated for each Persistent Class created. The ZCL_MY_FLIGHT, outlined there in the bottom right-hand corner, is the Persistent Class that we are going to create in just a few moments. It has to implement the IF_OS_STATE interface, which ensures that all persistent objects can be accessed in the same way. As you can see, this class has numerous attributes and GET/SET methods as many fields exist in its connected persistent structure that was generated by the Class Builder. For each Persistent Class two agent classes are generated by the Class Builder, an abstract and a final. As you can see here, the ZCA_MY_FLIGHT, on the bottom left, is one of our Agent classes, and its responsibility is to manage the ZCL_MY_FLIGHT Persistent Objects on the bottom right- (actually all the SQL statements take place in this ZCA Agent class), so it serves as a kind of data repository. ZCB_MY_FLIGHT, located right above ZCA_MY_FLIGHT, is the super class of ZCA_MY_FLIGHT and is also generated by the Class Builder. It implements the following interfaces: IF_OS_FACTORY, IF_OS_CA_PERSISTENCY, IF_OS_CA_INSTANCE.
• #8: So now that we’re a little more familiar with the concepts and components of persistence, let’s take a look at a few examples. Let’s begin by using the transaction SE24 to start the Class Builder. There you want to create a new class with the name, ZCL_MY_FLIGHT… as you can see we have done here in the screenshot. It is going to be the Persistent Class of the database table, called SFLIGHT. So, after filling in all the required fields such as “Class Name” and “Description” make sure to then select the class type, Persistent Class. Then click “SAVE” and select the package where you want to store the new class. In our example here, we are creating our classes in the temporary directory “$TMP” Once that is done- click Save again. So now, if you start transaction SE80 and navigate to your local temporary directory you will see the list of the newly created classes: ZCA_... ZCB_.... ZCL_......
• #9: After saving the new class, we can verify exactly what Persistent Class means. As you can see, under the Interface tab, it implements the interface, IF_OS_STATE (like I showed you a few moments ago in the diagram).
• #10: It is also friend of our abstract Agent class, ZCB_MY_FLIGHT, as seen here under the Friends tab.
• #11: Now that we’re a little more familiar with the basics of our Persistent Class, let’s connect it to an ABAP Dictionary object. Begin by setting its Persistence Mapping, by pushing the Persistence button.
• #12: After clicking on the persistence button (cp. Previous slide) the Pop-Up featured here will appear. Now we want to assign a table/view/ or structure to our class. So choose the database table that consists of flights, called SFLIGHT. You can do this by simply entering the name of the data dictionary you want to map - again it is the table: SFLIGHT Click the Continue icon, which is the green checkmark you see here, to confirm.
• #13: After assigning the table, Class Builder loads its metadata into the lower Tables/Fields section. Now double-click on any one of the fields in order to load it into the Maintain Area.
• #14: Using the Maintain Area, you can now modify the ID, description, and visibility of a field individually. After completing the maintenance of the given field, simply press ENTER in order to assign it to the Persistent Class as an attribute.
• #15: After pressing ENTER, the given field appears under the class as an attribute and loads the next field into the Maintain Area, where you perform the same workflow. So again, select each column / field you want to add to your class in the lower area of the screen. Double click on the name, then it appears in the middle Maintain Area section of the screen. Click the black arrow icon to add it to the class then it appears in the upper area Repeat this process for each field from the table (here: SFLIGHT) that you wish to add In our example, we want to add all columns from table SFLIGHT to our class (in the next slide you’ll see that once we do this, the lower area is empty and all columns are listed in the upper area)
• #16: If not all fields from a table are required no worries, the unused columns can remain in the lower area. The fields can be added later again in the same way like we did here. After applying the same workflow for each field, the attributes under our class appear, as seen here:
• #17: After saving the persistence mapping, return to the class definition using transaction SE80 or SE24 to see the components of the class. Navigate to the directory where you have created the classes to view the structure and components. Verify the generated attributes, based on the mappings you have selected.
• #18: Along with the new attributes, GET and SET methods are also generated. Please note that besides the Persistent Class, the Class Builder activates the Actor classes and all generated objects also. This will run automatically by saving your work! That's it! Now, you have a Persistent Class, called ZCL_MY_FLIGHT that you can use in the system.
• #19: Along with the new attributes, GET and SET methods are also generated. Please note that besides the Persistent Class, the Class Builder activates the Actor classes and all generated objects also. This will run automatically by saving your work! That's it! Now, you have a Persistent Class, called ZCL_MY_FLIGHT that you can use in the system.
• #20: For the sake of simplicity, I’ll now show you the basic use of persistent objects in some easy to understand examples. I'm going to show you two different operations, displaying and creating. Let's first check the display operation via the sample screenshot here. In the core of the TRY-CATCH block in line 9, you can see that we ask a reference of our agent class and save it in the reference variable lo_flight_agent by querying the class attribute of the ZCA_MY_FLIGHT called agent.
• #21: Then, we simply ask the agent to retrieve a persistent entry from the database with the “BA” business key. That can be seen here in lines 12 – 14. The “get_persitent”-call requires all primary keys from the database in order to identify a unique entry – here you see Carrier ID, Connection ID and Flight Date. Save the receiving reference of the flight instance in the reference variable, in the local object, called lo_flight (cp. Here you can see that in Line 12). From now on, you have an initialized instance of the ZCL_MY_FLIGHT(that is, the data came from the database), and can call its GET/SET methods, such as GET_PRICE() (cp. As seen in Line 17).
• #22: This process is very effective, and reusable among various clients, such as ABAP programs, ABAP classes, Function Modules, and so on. Here, as you can see here, you can verify the result:
• #23: The next example I want to share is to create a flight object using the Persistent Class, by referencing the agent class in the same way as we did previously, and saving it in the variable, lo_flight_agent. Ask the agent to create a persistent in the database with key export parameters (= these are the primary keys of the database table SFLIGHT): So that would be: ‘i_CARRID’ for key field Carrier ID, ‘i_CONNID’ for key field Connection ID ‘i_FLDATE‘ for key field Flight Date Then set a new price. 999999999 Again, these are the key values of the database table SFLIGHT. You can see that here, in the screenshot. At last, there is nothing left to do but commit the work (using the COMMIT statement), then save it. Now run the report- and a new record appears in the table.
• #24: Here you can check the result of the code: You can see our new entry in the first line – the price we set in our sample program shows, that we’ve created it -> 999999999 (cp. Code snippet from previous slide, line16).
• #25: QUESTIONS TO BE ANSWERED: Question: I created a new class and now I want to add a new column to the flight table – How do I do this? Or is it automatically created as an attribute? Answer: Sure – showcase…. Question: You talked about two object status, one is persistent and the other one is transient – Is it possible to use a transient object? Could you clarify please?! Answer: Persistent objects will be stored / changed and persisted on the database for later use for example Transient object will only have a livetime during the runtime e.g. like objects that support the process and that are not required to be stored on database, e.g. service objects etc. Question: Can I define a dedicated time when the data is stored or does this happen automatically? Answer: You can force persisting the data by sending a commit statement in your coding or you leave it to the process / LUW you are in. The final commit of your LUW will store the data.