Dynamic Programming in ABAP – Part 2 – Introduction to Data Reference
In my last blog I explained about field symbols, below is the link for same:
In this blog I am going to explain about data references and its significance in dynamic programming.
According to SAP documentation, Data references can point to any data objects or to their parts (components, rows of internal tables, or sections specified by offsets and lengths).
So data references are nothing but pointers. It stores the memory address of any data object. But to access the actual data object which data reference is pointing to, we first need to deference it using dereferencing operator ->*.
Difference between field symbol and data reference:
Field symbol is a placeholder for data object to which it is assigned and points to the content of data object hence it can be used at any operand position (no need to dereference it) and works with the content of the referenced memory area (value semantics).
Data references are pointers to data objects and it contains the memory address of data object (reference semantics). Data reference cannot be used at operand position directly; it should be dereferenced first.
Working with data reference:
There can be two types of data references:
- Typed Data Reference
- Generic Data Reference
Typed Data Reference:
Typed data reference variable can be declared as:
DATA lr_num TYPE REF TO i. CREATE DATA lr_num.
Here first statement declares a reference variable lr_num which can point to any data object of type “i”. And second statement creates an anonymous data object of type “i” and assigns the reference of this data object to lr_num. Now if we want to change the value of data object, then it can be done by dereferencing lr_num by using dereference operator ->* as shown below:
DATA lr_num TYPE REF TO i. CREATE DATA lr_num. lr_num->* = 2. WRITE: / lr_num->*.
The output will be 2.
- With ABAP 7.40, instead of CREATE DATA, the NEW operator can also be used to create an anonymous data object and assigns its reference to a data reference variable.
DATA lr_num TYPE REF TO i. lr_num = NEW #( ).
Assigning existing data object to data reference:
If you want to assign the reference of an existing data object to a data reference, you can use GET REFERENCE statement.
DATA: lv_num TYPE i VALUE 2. DATA: lr_num TYPE REF TO i. GET REFERENCE OF lv_num INTO lr_num. lr_num->* = 4. WRITE: / lv_num.
Here lv_num is an existing data object (not anonymous data object). The output would be 4.
- With ABAP 7.40, instead of GET REFERENCE, the REF operator also can be used to assign the reference of an existing data object to a data reference.
Working with structures:
DATA: lr_mara TYPE REF TO mara. CREATE DATA lr_mara. lr_mara->matnr = '1111'. lr_mara->matkl = '03'.
Here individual components of the structure can be accessed with -> operator on data reference variable.
Working with internal tables:
While processing internal table row, we can use REFERENCE INTO statement to set references to table rows as shown below:
DATA: lr_mara TYPE REF TO mara. DATA: lt_mara TYPE TABLE OF mara. SELECT * FROM mara INTO TABLE lt_mara UP TO 10 ROWS. LOOP AT lt_mara REFERENCE INTO lr_mara. WRITE: / lr_mara->matnr. ENDLOOP.
Generic Data Reference:
Generic data reference can be declared as:
DATA: lr_num TYPE REF TO data. CREATE DATA lr_num TYPE i.
Here first statement declares a generic data reference lr_num which can point to any data object. And second statement creates an anonymous data object of type “i” and assigns its reference to lr_num.
‘data’ in ABAP is a generic data type.
Now since lr_num is generic, lr_num->* cannot be directly used at operand position. Hence the below statement would not be allowed.
lr_num->* = 2.
So in case of generic data reference, it can only be dereferenced using a field symbol, and this field symbol can be used at any operand position to manipulate the value of data object as shown below:
DATA: lr_num TYPE REF TO data. FIELD-SYMBOLS: <num> TYPE any. CREATE DATA lr_num TYPE i. ASSIGN lr_num->* TO <num>. <num> = 3.
- After ASSIGN statement you should check sy-subrc If field symbol assignment is successful, sy-subrc will be 0 otherwise it will be 4.
Working with structures:
DATA: lr_str TYPE REF TO data. FIELD-SYMBOLS: <str> TYPE any. FIELD-SYMBOLS: <data> TYPE any. CREATE DATA lr_str TYPE mara. ASSIGN lr_str->* TO <str>. ASSIGN COMPONENT 'MATNR' OF STRUCTURE <str> TO <data>. <data> = '112'.
Here CREATE DATA statement creates an anonymous data object (MARA structure) and assigns its reference to the generic data reference lr_str, which then can be dereferenced into a generic field symbol <str>. Now, to access individual component of MARA structure, ASSIGN COMPONENT statement can be used.
Dynamically create data objects:
Requirement: Selection screen parameter “Table Name” will take a table name as input and display the corresponding table entries as output.
PARAMETERS: p_tname TYPE tabname. DATA: lr_tab TYPE REF TO data. FIELD-SYMBOLS: <tab> TYPE ANY TABLE. CREATE DATA lr_tab TYPE TABLE OF (p_tname). ASSIGN lr_tab->* TO <tab>. IF sy-subrc EQ 0. SELECT * FROM (p_tname) INTO TABLE <tab> UP TO 10 ROWS. cl_demo_output=>display( <tab> ). ENDIF.
Here lr_tab is a generic data reference and <tab> is a generic field symbol for internal table. In CREATE DATA statement, the type of data object is mentioned in parenthesis which means that the type will be determined at runtime based on the value of parameter p_tname. After that we have dereferenced the data reference lr_tab into a generic field symbol <tab>. Now this field symbol can be used to do any valid operation on the internal table.
Difference between data reference and object reference:
There are two types of reference variable:
- Data reference and
- Object reference
Data reference variable can store the reference to any data object (variable, structures, internal tables etc.) whereas Object reference variable can store the reference to any class object.
For data reference variables, either the generic data type or a completely specified data type can be specified. For object reference variables, either a class or an interface can be specified.
Thank you for reading.
In next blog, I have put one example of dynamic programming approach:
Can I ask you - what exactly is the point of these blogs?
I have quite a bit of ABAP experience but, to be honest, after reading this I'm none wiser on why would I need this if I'm not planning to re-invent SE16. If someone has trouble understanding ABAP Help, I doubt this would be of much help to them either.
Also posting the old syntax and then adding a note of 7.4 syntax could have been justified few years ago when it just became available. But these days I believe it should be the other way around: post current syntax and make a note of the old one. This is, however, all available in ABAP Help so, again, not sure what the point of this blog is...
I observed that sometimes, ABAP help lacks proper examples, so anyone who is very new in ABAP development may not be very comfortable in understanding ABAP help. Please correct me if i am wrong.
My point in this blog was to help the readers by showing that dynamic programming in ABAP is achieved using field symbols and data reference by putting some examples. Also the table display problem was just an example to show how to create data object dynamically.
I agree that i should have used 7.4 syntax, will keep this in mind in my future posts, thanks for your guidance 🙂
This may have been true many years ago but currently ABAP keyword documentation is available online and it has very good examples and thorough explanations, from what I see. Unfortunately, I can't find how to get a link to a specific article but this is a general link for documentation and a sample screenshot:
If someone is using ABAP Help in their outdated SAP system I'd encourage them to use online documentation to supplement it.
Another nice t-code for help is ABAPDOCU. It comes complete with documented program examples.
Jelena, So I strongly disagree with you!! I am a new ABAPer. After working with several other languages C++, Java, PHP and BPMS.
While I can read the documentation which can be verbose , I found this blog and his one on Field Symbols most useful to get up to speed quickly
Keep it up! 🙂
@Jelena - Humbly disagree.
SAP help language and examples can be tougher to understand for beginners. This is much more simpler and i benefited from it.
Thanks Rahul for the blog.
It's OK to disagree, different people - different opinions.
Yes, there are some ABAP Help (not to be confused with SAP Help) articles that are difficult to understand. But in this particular case personally I find ABAP documentation and examples quite adequate and language in this blog doesn't seem any simpler to understand to me (maybe I'm stupid, dunno 🙂 ). And I'm scratching my head on what exactly causes difficulties for the beginners in this case. So far the comments just state disagreement but it'd be nice to offer some specific examples, like what exactly is not clear in ABAP Help. (CC Horst Keller )
"So in case of generic data reference, it can only be dereferenced using a field symbol, and this field symbol can be used at any operand position to manipulate the value of data object as shown below" - could not find this clarity in the help documentation .
Also this single blog post summarizes data referencing and dereferencing in a more easy to understand manner than the help documentation, placing the concept in a single page.
This is stated in the documentation for TYPE REF TO data:
"A data reference variable typed generically with TYPE REF TO data can be dereferenced only in the statement ASSIGN with the dereferencing operator ->*."
If information in this blog helps you to understand something, that's great. But please always check the dates on these blogs (this one is 4 years old) and make sure to refer to the current documentation for the release you're working on to get most accurate information.
you can pass references to routines/methods as IMPORTING parameters, and still be able to change the referenced object. In this use case the IS BOUND predicate expression is useful to check if a data reference is valid.
Correct Jacques, I forgot to put this point.
We should always check if the data reference is valid using IS BOUND predicate, just like we use IS ASSIGNED for validating field symbol.
Again this is a nice start. I know that a lot of us are still on the older systems. (SAP GUI) So I tend to look for these "older" blogs. With that thought - it would help if this read less like a index from a book or a help doc. Perhaps a nice program to illustrate your points would be helpful instead of the small snippets. Show that one program that "encapsulates" what you are trying to do. I know you've written a dynamic program. Show it! Then maybe in pieces explain it.
Think more about what the business problem/demand caused you to write a dynamic program. Why? Easier to understand? Quicker to code? Multiple uses?
This really reads more like a help document.
Just a thought!
Do Keep blogging! Very few are brave enough to use the "older" technology and blog about it.
Thanks Michelle for your suggestions, I will try to put a good example demonstrating dynamic programming in next blog.
It's the best explanation I've ever seen. To be honest I prefer this snippets that seeking in a program the way to understand the topic. Thanks for posting.
Thank you for blogging about this concept often not well understood, and to summary the important notions all in one.
Just to nitpicking:
Excellent Blog indeed. Though there are several new syntaxes which has come up with SAP ABAP the business logic remains the same in SAP. Though we don't use new syntaxes as mentioned by Jelena Perfiljeva still we can write few blogs which are quite useful as per our requirements. We work for different customers for different scenario's i don't think all the requirements would be one and the same. in such cases our Blogs will be much useful for some one who are desperately looking for such scenario's . i wrote a blog for Inbound Delivery creation previously [Which you can't find any solution anywhere] and didn't used New ABAP Syntax. But still there are hundreds of users which found that useful. Jelena Perfiljeva though it useless and asked me the same question what's the use of that blog for her. i may be wrong here. but My intention is to help some one and share the knowledge according to our experience. so in this particular scenario we don't need to worry about new ABAP Syntax or other stuff, just that we're writing a blog which is useful for some needy.
Once Again Excellent Blog here. Much Appreciated.
Just reading this comment because it mentioned my old account. It seems your account is now inactive but for the record, I never made such derogatory comments on your blog. Anyone can read the actual comment text here together with your response. I'm quite surprised to read this statement here because your response in the blog comment was completely different.
Can someone please explain, how would the following statement be written with "NEW" keyword -
I understand that the below statement would be incorrect -
lr_tab = NEW (ptab)( ).
Thanks & Regards,