You have learned how to create database tables and ABAP dictionary types in part 14 and part 15 of our ABAP for...
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Newbies series. Now is a good time to create your first ABAP class, which works with this data.
Our first goal is an application which allows us to display and change the data of a selected customer. In this tip we will create the necessary ABAP object for this, and in the next one we will create the user interface with Web Dynpro. The intention is of course not to demonstrate a well thought-out, realistic example of object orientated modelling of a real business problem, which is a science in itself, and would go beyond the scope of this tip. Instead, we merely want to demonstrate how classes can be implemented in ABAP Objects in the form of a tiny example.
The customer class will have a constructor, a set of public attributes and a save method which stores changed attributes to the database.
To create an ABAP class go to the ABAP workbench SE80, select "Class/Interface” and enter the name YCL_CUSTOMER in the input field and hit enter.
Confirm the pop up and enter a description in the next window while leaving the other settings as they are.
Double click the YCL_CUSTOMER class on the left hand side (below "Object Name”) and select the Attribute tab on the right hand side, to create the attributes of the class. We choose a subset of the SCUSTOM database columns as attributes of our class. Select the Attributes tab and add the attributes based on the ABAP dictionary types used for the corresponding database table column:
ID TYPE S_CUSTOMER
NAME TYPE S_CUSTNAME
STREET TYPE S_STREET
POSTCODE TYPE POSTCODE
CITY TYPE CITY
COUNTRY TYPE S_COUNTRY
TELEPHONE TYPE S_PHONENO
EMAIL TYPE S_EMAIL
All attributes should be public Instance attributes, set by the Level and Visibility column. The result looks like this:
Of course we could also declare the attributes as private and offer setter and getter methods, which might be better style but let’s keep our example as simple as possible for the moment.
Let’s assume an application that wants to instantiate a customer object knows in most cases already the ID of the customer (by a query method of a customer manager class for example). Therefore we create a constructor for the class with the customer ID as an optional parameter. The constructor then gets the data of the customer and fills the object’s attributes with the values from the database.
To create a constructor, click on the Constructor button on the upper right hand corner, and the editor for the already existing but empty constructor method opens.
Click on "Parameters” to add the customer ID as optional (check checkbox in third column!) parameter of the dictionary type S_CUSTOMER.
Clicking on "Methods” will bring you back to the former view and a double click on the CONSTRUCTOR method opens the ABAP editor.
In the constructor we will first check if the customer ID has been provided or not, since it was declared as an optional parameter.
If the ID is available we select the data of the customer with this ID from the database into a structure. The structure type is available in the ABAP dictionary because the database table SCUSTOM is based on it. Sometimes people are confused that a table in the database (table=many lines) is represented as structure (=single line) in the ABAP dictionary, but for the moment lets simply accept this as a fact.
The structure is declared at the top of the method with the data: statement and filled with the Open SQL statement SELECT…FROM…INTO. The important point is that SQL is directly integrated into ABAP. You just type in the SQL statements into your ABAP code. The application server automatically gives you the connection to the database and hides completely the differences between the SQL dialects of different database which can drive programmers crazy. This is done via the "Open SQL” called layer in the application server, offering a unified SQL which is translated into the specific SQL dialect of the currently used database, making ABAP programming independent of the database vendors.
Then the attributes of the object instance are filled with the result we got from the database. A column, the so-called component of a structure, can be directly accessed with the "-" separator, for example the name of the customer is available as S_CUSTOMER-NAME.
The whole listing of the constructor method looks like:
* declaration of a structure matching the database table
DATA: s_customer TYPE scustom.
* check if ID parameter has been supplied
IF id IS SUPPLIED.
* get the data of the customer from the database
SELECT SINGLE * FROM scustom INTO s_customer WHERE id = id.
* fill the object's attributes with the data
me->id = id.
me->name = s_customer-name.
me->street = s_customer-street.
me->postcode = s_customer-postcode.
me->city = s_customer-city.
me->country = s_customer-country.
me->telephone = s_customer-telephone.
me->email = s_customer-email.
Type in the coding (and I recommend to type it rather than cut and paste), save and check the syntax of the method with the check button. If no errors occur you can activate the class with the button next to the check button.
A special feature of the ABAP workbench is that it contains a test environment which you can use out of the box to test and execute your ABAP coding directly without the need of writing a test program. After you have successfully activated your class click on the test button and the workbench will display the following:
This screen is a built in test feature of the ABAP workbench. It automatically generates a test UI for an ABAP class based on its methods and attributes. The first screen offers all static public methods of a class, in our case only the constructor with its single parameter. Choose for example 00000001 as customer ID (1.) and click the instantiate button (2.). An object instance is created and its attributes are displayed:
We see the first customer in our dataset is a company named SAP AG, located in Walldorf, Germany. Unfortunately the data is already outdated. Last year the city of Walldorf renamed the Neurottstrasse to Dietmar-Hopp-Allee in honour of the founder and former CEO of SAP. Although we can change the street name due to the public attributes we still need a method which allows us to save the changed data to the database.
To create this new method go back to the class builder with the green back button click the Methods tab and go into change mode. Create a new method SAVE as public instance method. A double click on SAVE leads you to the editor. The code to save the current attribute values to the database is pretty simple:
* declaration of structure
DATA: s_customer TYPE scustom.
* fill structure with current attribute values
s_customer-id = me->id.
s_customer-name = me->name.
s_customer-street = me->street.
s_customer-postcode = me->postcode.
s_customer-city = me->city.
s_customer-country = me->country.
s_customer-telephone = me->telephone.
s_customer-email = me->email.
* update the data in the DB
MODIFY scustom FROM s_customer.
It is necessary to put the current attribute values into a structure first, because the SQL statements for updating or modifying database tables need the values in a structure matching the database table structure. The MODIFY keyword is the Open SQL statement for either updating an existing dataset or creating a new one. (We could have choosen here also the UPDATE statement, but we want to enhance the class later also with the capability to create and save new entries into the database, therefore we chose the MODIFY.) Enter the code into the method and activate the class.
If you now click the Test button and instantiate the customer 00000001, the test environment will display also the new SAVE method.
Now we can correct the address to Dietmar Hopp Allee 16 (2.). Check the Upper/lower case active checkbox (1.), otherwise the data will be converted to uppercase and click on the clock/run icon (3.) right to the SAVE method.
Now the data is updated and if you call the test again or look into the database table with the transaction SE16 it will display the new address.
Although the integrated test capabilities of the ABAP workbench are quite useful for test purposes, we want to have a "real” application example in the end, of course. With our first ABAP class, we can start with creating a user interface in Web Dynpro, which allows to display, change and save customer addresses in the next tip.
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