Introduction to OData in SAP
OData (Open Data Protocol) is an open standard protocol
used to build and consume RESTful APIs. SAP utilizes OData services for
efficient data access and communication between the SAP system and external
applications like SAP Fiori, SAP UI5, or even non-SAP systems like .NET, Java,
or PHP. This allows for smooth integration between the backend system and the
frontend, enabling users to build modern, lightweight, and interactive
applications.
Difference Between SAP ABAP Apps and UI5/Fiori
Apps
ABAP
Apps
In traditional SAP ABAP applications:
- Execution at the Backend: Most of the code, including
UI elements like dropdowns and radio buttons, are handled by the backend system
(i.e., SAP server).
- Event Handling: All event-related code and validations
are processed on the server side.
- Database Operations: Any database operations like SELECT,
DELETE, INSERT, and UPDATE are executed at the database.
- Server Load: Since 90% of the processing is done on the
server side, ABAP apps are stateful. This means the server remains busy
managing the user session, potentially degrading performance under heavy load.
- Heavy Screens: ABAP applications have GUI-based,
heavier screens that are not well-suited for modern web interfaces.
- Limited Web Features: ABAP applications do not support
web-based functionalities like Fiori and UI5 apps.
UI5/Fiori Apps
UI5 and Fiori applications, on the other hand, offer:
- Frontend Execution: Screen-related code, event
handling, and validations are handled on the frontend.
- Backend Operations: Only database operations (SELECT, INSERT,
DELETE, UPDATE) are executed on the server side.
- Stateless Nature: These applications are stateless,
meaning the server is not overloaded with managing user sessions, which results
in better performance.
- Lightweight: They are lightweight browser-based
applications that are responsive and can run on multiple devices.
- Modern UI: UI5/Fiori apps provide a modern, flexible,
and mobile-friendly interface.
- HTTP-based: They operate based on HTTP requests and
responses, making them suitable for web environments.
OData
Architecture in SAP
SAP supports OData through the following components:
1. SAP Network Gateway (OData ABAP services): For
handling backend ABAP data.
2. SAP HANA XS Engine (OData HANA services): Specific for
accessing HANA database data.
3. OData External Services: Used for integrating with
non-SAP systems.
OData services are primarily executed under the SAP
NetWeaver Gateway component. This gateway supports two formats:
- XML
- JSON (Preferred for being lightweight and faster in
performance)
SAP
OData Service Development
The main purpose of SAP OData services is to allow
external applications to perform database operations (like read, write, update,
or delete) via an easy-to-use RESTful API.
T-Code for
OData Development: SEGW
In SAP, the transaction code SEGW is used for creating
OData services. Every OData project in SAP has four main components:
1. Data Model
2. Service Implementation
3. Runtime Artifacts
4. Service Maintenance
1.
Data Model
The Data Model defines the structure of the data that
will be exposed through the OData service. Key elements of the data model are:
- Entity Type: This is a collection of fields, similar to
a structure in ABAP, which defines the schema of the data.
- Entity: It holds a single record at a time, like a work
area in ABAP.
- Entity Set: A collection of records, similar to an
internal table in ABAP.
- Association: Defines the relationship between two
entity types.
- Association Set: Establishes a relationship between two
entity sets.
2.
Service Implementation
Service implementation involves defining the CRUD
operations for the OData service. CRUD refers to:
- Create: Handled by the CREATE_ENTITY() method.
- Read:
- Single entity: GET_ENTITY() method, similar
to SELECT SINGLE.
- Multiple
entities: GET_ENTITYSET() method, similar to SELECT *.
- Update: Handled by the UPDATE_ENTITY() method to update
records.
- Delete: Handled by the DELETE_ENTITY() method to remove
records.
3.
Runtime Artifacts
Runtime artifacts are auto-generated classes that handle
the execution of OData services:
- _MPC (Model Provider Class): Defines the data model of
the service.
- _MPC_EXT (Model Provider Extension Class): Allows
developers to extend the data model with custom logic.
- _DPC (Data Provider Class): Contains the logic for CRUD
operations.
- _DPC_EXT (Data Provider Extension Class): Allows
developers to extend the service logic with custom implementation.
- _SRV: Registered services.
- _MDL: Registered model.
4.
Service Maintenance
Once the OData service is developed, it needs to be
registered and maintained. This involves:
- Error Logs: To trace and find errors that occur during
the execution of the OData service.
- Gateway Client: A temporary screen provided by SAP to
test the functionality of the OData service.
Advantages of OData Services
- Front-End Agnostic: OData services are independent of
the front-end technology. You can consume them in SAP UI5, Fiori, or even
non-SAP applications like .NET, Java, or PHP.
- Supports Multiple Formats: OData services support both
XML and JSON formats, with JSON being the preferred choice due to its
lightweight nature.
- Efficient Data Access: Since OData is based on REST, it
allows efficient communication between frontend and backend, which is
especially beneficial for SAP Fiori and UI5 applications.
Key
Takeaways
- ABAP Applications are stateful and execute most of
their code on the server side, leading to a heavy server load.
- UI5/Fiori Applications are stateless, execute
frontend-related code on the client side, and only execute database operations
on the server.
- OData Services allow the smooth integration of backend
ABAP data with frontend applications like SAP Fiori and external systems. They
are lightweight, front-end agnostic, and follow the REST architecture.
- T-code SEGW is used for creating OData services, with
four main components: Data Model, Service Implementation, Runtime Artifacts,
and Service Maintenance.
By understanding OData services, ABAP developers can
unlock the full potential of SAP’s modern programming model, creating flexible,
lightweight, and efficient applications that run smoothly in today’s
multi-device, web-based environment.
Here are some key interview questions and answers based
on the Odata.
1. What is OData,
and why is it used in SAP?
Answer:
OData (Open Data Protocol) is a standard protocol used
for building and consuming RESTful APIs. In SAP, OData services are used to
facilitate communication between the backend (SAP system) and frontend
applications like SAP Fiori or even non-SAP systems like .NET, PHP, etc. OData
enables smooth integration and allows for efficient data access, providing
flexibility in building lightweight web-based applications.
2. What is the
main difference between ABAP apps and UI5/Fiori apps?
Answer:
- ABAP Apps:
- Stateful
applications where most of the code execution (including UI-related elements)
happens on the server side.
- Heavy GUI-based
screens.
- Performance is
impacted as the server is overloaded with session management.
- UI5/Fiori Apps:
- Stateless
applications where UI-related code is executed on the frontend.
- Lightweight
browser-based screens that are responsive and mobile-friendly.
- Server is
mainly used for database operations, improving performance.
3. What is the
architecture of OData in SAP?
Answer:
OData services in SAP follow this architecture:
1. SAP Network Gateway (OData ABAP Services): For
ABAP-based backend data.
2. SAP HANA XS Engine (OData HANA Services): For handling
HANA-specific data.
3. OData External Services: Used for integration with
non-SAP applications.
OData is primarily executed under the SAP NetWeaver
Gateway component, which supports XML and JSON formats (with JSON being
preferred due to its lightweight nature).
4. What are the
main types of OData services in SAP?
Answer:
There are three main types of OData services in SAP:
1. OData ABAP Services: Used for traditional ABAP-based
systems.
2. OData HANA Services: For working with SAP HANA
databases.
3. OData External Services: For non-SAP applications or
external systems.
5. Explain the key
components of an OData service project in SAP.
Answer:
An OData project in SAP contains the following
components:
1. Data Model: Defines the structure of data using Entity
Types, Entity Sets, and Associations.
2. Service Implementation: Implements CRUD (Create, Read,
Update, Delete) operations.
- CREATE_ENTITY(),
GET_ENTITY(), GET_ENTITYSET(), UPDATE_ENTITY(), DELETE_ENTITY().
3. Runtime Artifacts: Includes auto-generated classes
like _MPC, _DPC, and their extensions (_MPC_EXT, _DPC_EXT).
4. Service Maintenance: Involves error logging, and
testing the service using the Gateway Client.
6. What are CRUD
operations in OData services, and how are they implemented?
CRUD stands for Create, Read, Update, and Delete. In
OData services:
- CREATE_ENTITY(): Handles create operations.
- GET_ENTITY(): Reads a single record, similar to SELECT
SINGLE.
- GET_ENTITYSET(): Reads multiple records, similar to SELECT
*.
- UPDATE_ENTITY(): Updates a record.
- DELETE_ENTITY(): Deletes a record.
These methods are implemented in the _DPC_EXT (Data
Provider Extension Class), which can be customized based on business
requirements.
7. What is the
difference between Entity Type, Entity, and Entity Set in OData?
Answer:
- Entity Type: Defines the structure of the data with
fields, data types, and lengths, similar to a structure in ABAP.
- Entity: Holds a single record at a time, like a work
area in ABAP.
- Entity Set: Holds a collection of records, similar to
an internal table in ABAP.
8. What are the
runtime artifacts generated during OData service creation?
Answer:
The runtime artifacts generated are:
- _MPC (Model Provider Class): Defines the data model.
- _MPC_EXT (Model Provider Extension Class): Extends the
data model with custom logic.
- _DPC (Data Provider Class): Handles CRUD operations.
- _DPC_EXT (Data Provider Extension Class): Extends CRUD
functionality with custom implementations.
- _SRV: Registered services.
- _MDL: Registered model.
These classes help in managing the execution of the OData
service.
9. What is the
role of the SAP NetWeaver Gateway in OData?
Answer:
SAP NetWeaver Gateway acts as the middleware that
processes OData requests and responses. It converts backend data into formats
like XML or JSON that are consumable by frontend applications (like Fiori, UI5,
or external systems). The gateway handles HTTP requests and provides necessary
services for OData communication between the frontend and backend systems.
10. What is the
purpose of the Gateway Client in OData?
Answer:
The Gateway Client is a tool provided within the SAP
NetWeaver Gateway (accessible via transaction code SEGW). It is used to test
the functionality of OData services. Developers can execute HTTP requests and
check the responses, trace errors, and validate the correct functioning of
their OData service implementations.
11. Explain the
relationship between Entity Types and Associations in OData.
Answer:
In OData:
- Entity Types define individual data structures.
- Associations represent relationships between two entity
types. For example, an association can define a relationship between a customer
and their orders.
An Association Set is used to define a relationship
between two entity sets, establishing a link between collections of records in
the OData model.
12. How does OData
support different frontend technologies like UI5, Fiori, or even non-SAP
systems?
Answer:
OData is frontend-agnostic, meaning it can be consumed by
various frontend technologies. Whether it's SAP UI5/Fiori or non-SAP
applications (like PHP, .NET, or Java), OData provides a uniform way to access
SAP backend data via RESTful APIs. This flexibility makes it ideal for modern
application development, where the frontend could be anything from a web app to
a mobile app.
13. Why is JSON
preferred over XML in OData services?
Answer:
JSON is the preferred format in OData services because it
is lightweight and easier to parse compared to XML. JSON leads to faster data
transfer and better performance, especially in web-based applications where
minimizing the payload size is critical for optimal user experience.
14. What is the
advantage of using OData services over traditional SAP methods?
Answer:
OData services offer several advantages:
- Lightweight and stateless architecture, which results
in better performance.
- Platform-independent: They can be consumed by any
front-end technology.
- Supports multiple formats: Both XML and JSON are
supported, giving flexibility in how data is consumed.
- Modern integration: OData enables seamless integration
between SAP and modern web or mobile applications.
15. Can you
explain what Code Pushdown is and how it relates to OData and HANA?
Answer:
Code Pushdown is the concept where heavy data processing
is pushed from the application server to the database layer, especially
relevant in SAP HANA. In OData services, instead of fetching large volumes of
data to the application server for processing, HANA performs operations
directly at the database level, leading to faster data retrieval and reduced
application server load.