Archive | April 2012

Developer’s Journal: HANA Catalog Access from ABAP

Introduction

In my last blog, I introduced the topic of ABAP Secondary Database Connection and the various options for using this technology to access information in a HANA database from ABAP. Remember there are two scenarios where ABAP Secondary Database Connection might be used.  One is when you have data being replicated from an ABAP based application to HANA. In this case the ABAP Data Dictionary already contains the definitions of the tables which you access with SQL statements.

The other option involves using HANA to store data gathered via other means.  Maybe the HANA database is used as the primary persistence for completely new data models.  Or it could be that you just want to leverage HANA specific views or other modeled artifacts upon ABAP replicated data.  In either of these scenarios, the ABAP Data Dictionary won’t have a copy of the objects which you are accessing via the Secondary Database Connection. Without the support of the Data Dictionary, how can we define ABAP internal tables which are ready to receive the result sets from queries against such objects?

In this blog, I want to discuss the HANA specific techniques for reading the Catalog and also how the ABDC classes could be used to build a dynamic internal table which matches a HANA table or view.  The complete source code discussed in this blog can be downloaded from the SCN Code Exchange.

HANA Catalog

The first task is figuring out how to read metadata about HANA tables and views.  When access these objects remotely from ABAP, we need to be able to prepare ABAP variables or internal tables to receive the results.  We can’t just declare objects with reference to the data dictionary like we normally would.  Therefore we need some way to access the metadata which HANA itself stores about its tables, views, and their fields.

HANA has a series of Catalog objects.  These are tables/views from the SYS Schema. Some of the ones which we will use are:

  • SCHEMAS – A list of all Schemas within a HANA database.  This is useful because once we connect to HANA via the Secondary Database Connection we might need to change from the default user Schema to another schema to access the objects we need.
  • DATA_TYPES – A list of all HANA built-in data types. This can be useful when you need the detail technical specification of a data type used within a table or view column.
  • TABLES – A list of all tables and their internal table ID.  We will need that table ID to look up the Table Columns.
  • TABLE_COLUMNS – A listing of columns in a Table as well as the technical information about them.
  • VIEWS –  A list of all views and their internal view ID.  We will need that View ID to look up the View Columns. We can also read the View creation SQL for details about the join conditions and members of the view.
  • VIEW_COLUMNS – A listing of columns in a View as well as the technical information about them.

Now reading these views from ABAP can be done exactly as we discussed in the previous blog.  You can use the Secondary Database Connection and query them with ABDC, for example. Here is the code I use to query the SCHEMAS view:

gr_sql_con = cl_sql_connection=>get_connection( gv_con_name ).
 create object gr_sql
 exporting
 con_ref = gr_sql_con.
data lr_result type ref to cl_sql_result_set.
 lr_result = gr_sql->execute_query(
 |select * from schemas| ).
data lr_schema type ref to data.
 get reference of rt_schemas into lr_schema.
 lr_result->set_param_table( lr_schema ).
 lr_result->next_package( ).
 lr_result->close( ).

Personally I figured it might be useful to have one utility class which can read from any of these various catalog views.  You can download this class from here. Over the next few blogs in this series I will demonstrate exactly what I built up around this catalog utility.

ABAP Internal Tables from ABDC

I originally had the idea that I would read the TABLE_COLUMNS View from the HANA catalog and then use the technical field information to generate a corresponding ABAP RTTI and dynamic internal table. My goal was to make queries from tables which aren’t in the ABAP data dictionary much easier.  As it turns out, I didn’t need to directly read this information from the catalog views because the ADBC already had functionality to support this requirement.

The ADBC result set object (CL_SQL_RESULT_SET), has a method named GET_METADATA. This returns an ABAP internal table with all the metadata about which every object you just queried.  Therefore I could build a generic method which takes in any HANA Table or View and does a select single from it.  With the result set from this select single, I could then capture metadata for this object.

METHOD get_abap_type.
 DATA lr_result TYPE REF TO cl_sql_result_set.
 lr_result = gr_sql->execute_query(
 |select top 1 * from { obj_name_check( iv_table_name ) }| ).
 rt_meta = lr_result->get_metadata( ).
 lr_result->close( ).
ENDMETHOD.

For example if I run this method for my ABAP Schema on table SFLIGHT I get the following information back:

Of course the most value comes when you read an object which doesn’t exist in the ABAP Data Dictionary.  For example, I could also read one of the HANA Catalog Views: SCHEMAS

This metadata might not seem like much information, but its enough to in turn generate an ABAP RTTI (RunTime Type Information) object. From the RTTI, I now can generate an ABAP internal table for any HANA table or view in only a few lines of code:

 DATA lr_tabledescr TYPE REF TO cl_abap_tabledescr.
 lr_tabledescr = cl_abap_tabledescr=>create(
 p_line_type  = me->get_abap_structdesc( me->get_abap_type( iv_table_name ) ) ).
 CREATE DATA rt_data TYPE HANDLE lr_tabledescr.

This all leads up to a simple method which can read from any HANA table and return an ABAP internal table with the results:

METHOD get_abap_itab.
*@78QImporting@  IV_TABLE_NAME  TYPE STRING
*@78QImporting@  IV_MAX_ROWS  TYPE I  DEFAULT 1000
*@7BQReturning@  value( RT_DATA )  TYPE REF TO DATA
*@03QException@  CX_SQL_EXCEPTION
DATA lr_result TYPE REF TO cl_sql_result_set.
IF iv_max_rows IS SUPPLIED.
 lr_result = gr_sql->execute_query(
 |select top { iv_max_rows } * from { obj_name_check( iv_table_name ) }| ).
 ELSE.
 lr_result = gr_sql->execute_query(
 |select * from { obj_name_check( iv_table_name ) }| ).
ENDIF.
 DATA lr_tabledescr TYPE REF TO cl_abap_tabledescr.
 lr_tabledescr = cl_abap_tabledescr=>create(
 p_line_type  = me->get_abap_structdesc( me->get_abap_type( iv_table_name ) ) ).
 CREATE DATA rt_data TYPE HANDLE lr_tabledescr.
 lr_result->set_param_table( rt_data ).
 lr_result->next_package( ).
 lr_result->close( ).
ENDMETHOD.

CLOSING

Between the HANA Catalog objects and the ADBC functionality to read type information, I’ve now got all the pieces I need to perform dynamic queries against any HANA table or view. Ultimately I could use this functionality to build all kinds of interesting tools. In fact I’m already playing around with a generic catalog/data browser; but that’s something to look forward to in a future blog.

 

 

Enterprise Geeks Podcast – Code Jam and SAPPHIRE/ASUG Annual Conference Prep

We are ready to rock to Van Halen at SAPPHIRE in our kilts

Season 4 Episode 13

Its luck episode number 13 of season 4 — if only we could have done the recording last Friday the 13th.  After several weeks of travel, we finally got most of the gang together to record a podcast.  We discuss the SAP Database and Mobility press conference from the previous week as well as upcoming plans for SAPPHIRE/ASUG Annual Conference. Craig also announces the new Code Jam events and talks about his vision for where this series of events will be headed.

Running Time: 45:23

If you have questions, suggestions, or topic ideas for future episodes, give us a shout here.

DJ Adams and a trip down technology lane

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Craig Cmehil managed to catch a quick chat with DJ Adams recently in Germany and they discussed everything from MAPICS to SAPUI5 to Gateway and how the past is reconnecting the present.

DJ Adams is an enterprise architect and open source programmer, author, and bread-maker living in Manchester. He has a degree in Latin & Greek (Classics) from the University of London, and despite having been referred to as an alpha geek, can nevertheless tie his own shoelaces and drink beer without spilling it.

So many things discussed… WOW! Big thanks to DJ for joining in.

Direct Download Link: https://enterprisegeeks.com/podcasts/eGeeks_DJAdams_March_2012.m4a

Developer’s Journal: ABAP/HANA Connectivity via Secondary Database Connection

Introduction

In this first edition of this HANA Developer’s Journey I barely scratched the surface on some of the ways which a developer might begin their transition into the HANA world. Today I want to describe a scenario I’ve been studying quite a lot in the past few days: accessing HANA from ABAP in the current state.  By this, I mean what can be built today.  We all know that SAP has some exciting plans for ABAP specific functionality on top of HANA, but what everyone might not know is how much can be done today when HANA runs as a secondary database for your current ABAP based systems.  This is exactly how SAP is building the current HANA Accelerators, so it’s worth taking a little time to study how these are built and what development options within the ABAP environment support this scenario.

HANA as a Secondary Database

The scenario I’m describing is one that is quite common right now for HANA implementations.  You install HANA as a secondary database instead of a replacement for your current database.  You then use replication to move a copy of the data to the HANA system. Your ABAP applications can then be accelerated by reading data from the HANA copy instead of the local database. Throughout the rest of this blog I want to discuss the technical options for how you can perform that accelerated read.

ABAP Secondary Database Connection

ABAP has long had the ability to make a secondary database connection.  This allows ABAP programs to access a database system other than the local database. This secondary database connection can even be of a completely different DBMS vendor type. This functionality is extended to support SAP HANA for all the NetWeaver release levels from 7.00 and beyond. Service Note 1517236  (for SAP Internal) or Note  1597627  (for everyone) lists the preconditions and technical steps for connection to HANA systems and should always be the master guide for these preconditions, however I will summarize the current state at the time of publication of this blog.

Preconditions

  • SAP HANA Client is installed on each ABAP Application Server. ABAP Application Server Operating System must support the HANA Client (check Platform Availability Matrix for supported operating systems).
  • SAP HANA DBSL is installed (this is the Database specific library which is part of the ABAP Kernel)
  • The SAP HANA DBSL is only available for the ABAP Kernel 7.20
    • Kernel 7.20 is already the kernel for NetWeaver 7.02, 7.03, 7.20, 7.30 and 7.31
    • Kernel 7.20 is backward compatible and can also be applied to NetWeaver 7.00, 7.01, 7.10, and 7.11
  • Your ABAP system must be Unicode

Next, your ABAP system must be configured to connect to this alternative database. You have one central location where you maintain the database connection string, username and password.  Your applications then only need to specify the configuration key for the database making the connection information application independent.

This configuration can be done via table maintenance (Transaction SM30) for table DBCON. From the configuration screen you supply the DBMS type (HDB for HANA), the user name and password you want to use for all connections and the connection string. Be sure to include the port number for HANA systems. It should be 3<Instance Number>15. So if your HANA Database was instance 01, the port would be 30115.

DBCON can also be maintained via transaction DBACOCKPIT. Ultimately you end up with the same entry information as DBCON, but you get a little more information (such as the default Schema) and you can test the connection information from here.

 

Secondary Database Connection Via Open SQL

The easiest solution for performing SQL operations from ABAP to your secondary database connection is to use the same Open SQL statements which ABAP developers are already familiar with. If you supply the additional syntax of CONNECTION (dbcon), you can force the Open SQL statement to be performed against the alternative database connection.

For instance, let’s take a simple Select and perform it against our HANA database:

  SELECT * FROM sflight CONNECTION ('AB1')
    INTO TABLE lt_sflight
   WHERE carrid = 'LH'.

The advantage of this approach is in its simplicity.  With one minor addition to existing SQL Statements you can instead redirect your operation to HANA. The downside is that the table or view you are accessing must exist in the ABAP Data Dictionary. That isn’t a huge problem for this Accelerator scenario considering the data all resides in the local ABAP DBMS and gets replicated to HANA. In this situation we will always have local copies of the tables in the ABAP Data Dictionary.  This does mean that you can’t access HANA specific artifacts like Analytic Views or Database Procedures. You also couldn’t access any tables which use HANA as their own/primary persistence.

Secondary Database Connection Via Native SQL

ABAP also has the ability to utilize Native SQL. In this situation you write you database specific SQL statements.  This allows you to access tables and other artifacts which only exist in the underlying database.  There is also syntax in Native SQL to allow you to call Database Procedures.  If we take the example from above, we can rewrite it using Native SQL:

EXEC SQL.
    connect to 'AB1' as 'AB1'
  ENDEXEC.
  EXEC SQL.
    open dbcur for select * from sflight where mandt = :sy-mandt and carrid = 'LH'
  ENDEXEC.
  DO.
    EXEC SQL.
      fetch next dbcur into :ls_sflight
    ENDEXEC.
    IF sy-subrc NE 0.
      EXIT.
    ELSE.
      APPEND ls_sflight TO lt_sflight.
    ENDIF.
  ENDDO.
  EXEC SQL.
    close dbcur
  ENDEXEC.
  EXEC SQL.
    disconnect 'AB1'
  ENDEXEC.

Its certainly more code than the Open SQL option and a little less elegant because we are working with database cursors to bring back an array of data.  However the upside is access to features we wouldn’t have otherwise. For example I can insert data into a HANA table and use the HANA database sequence for the number range or built in database functions like now().

    EXEC SQL.
      insert into "REALREAL"."realreal.db/ORDER_HEADER"
       values("REALREAL"."realreal.db/ORDER_SEQ".NEXTVAL,
                   :lv_date,:lv_buyer,:lv_processor,:lv_amount,now() )
    ENDEXEC.
    EXEC SQL.
      insert into "REALREAL"."realreal.db/ORDER_ITEM" values((select max(ORDER_KEY)
        from "REALREAL"."realreal.db/ORDER_HEADER"),0,:lv_product,:lv_quantity,:lv_amount)
    ENDEXEC.

The other disadvantage to Native SQL via EXEC SQL is that there are little to no syntax checks on the SQL statements which you create. Errors aren’t caught until runtime and can lead to short dumps if the exceptions aren’t properly handled.  This makes testing absolutely essential.

Secondary Database Connection via Native SQL – ADBC

There is a third option that provides the benefits of the Native SQL connection via EXEC SQL, but also improves on some of the limitations.  This is the concept of ADBC – ABAP Database Connectivity.  Basically it is a series of classes (CL_SQL*) which simplify and abstract the EXEC SQL blocks. For example we could once again rewrite our SELECT * FROM SFLIGHT example:

****Create the SQL Connection and pass in the DBCON ID to state which Database Connection will be used
  DATA lr_sql TYPE REF TO cl_sql_statement.
  CREATE OBJECT lr_sql
    EXPORTING
      con_ref = cl_sql_connection=>get_connection( 'AB1' ).

****Execute a query, passing in the query string and receiving a result set object
  DATA lr_result TYPE REF TO cl_sql_result_set.
  lr_result = lr_sql->execute_query(
    |SELECT * FROM SFLIGHT WHERE MANDT = { sy-mandt } AND CARRID = 'LH'| ).

****All data (parameters in, results sets back) is done via data references
  DATA lr_sflight TYPE REF TO data.
  GET REFERENCE OF lt_sflight INTO lr_sflight.

****Get the result data set back into our ABAP internal table
  lr_result->set_param_table( lr_sflight ).
  lr_result->next_package( ).
  lr_result->close( ).

Here we at least remove the step-wise processing of the Database Cursor and instead read an entire package of data back into our internal table at once.  By default the initial package size will return all resulting records, but you can also specify any package size you wish thereby tuning processing for large return result sets.  Most importantly for HANA situations, however, is that ADBC also lets you access non-Data Dictionary artifacts including HANA Stored Procedures.  Given the advantages of ADBC over EXEC SQL, it is SAP’s recommendation that you always try to use the ADBC class based interfaces.

Closing

This is really just the beginning of what you could with this Accelerator approach to ABAP integration into SAP HANA. I’ve used very simplistic SQL statements in my examples on purpose so that I could instead focus on the details of how the technical integration works.  However, the real power comes when you execute more powerful statements (SELECT SUM … GROUP BY), access HANA specific artifacts (like OLAP Views upon OLTP tables), or database procedures.  These are all topics which I will explore more in future editions of this blog.

Shout out to BCO6181

While at the Mastering SAP Technologies event in Sydney last week, loyal Enterprise Geek Tony de Thomasis (otherwise known as c821311 on Twitter) asked a few of us to give some advice to his students in BCO6181. It sounds like Tony has a great group of students which are already well on their way to creating the next generation of Enterprise Geeks.