Dear All,
I am writing this blog specifically for SMP 3.0 as from SMP 3.0 onwards the entire architecture is based on OData Framework. Be it any backend datasource, there is a concept of Entity Data Model (EDM) to expose your backend data in OData.
For SAP Backend systems, there are two ways to consume data from RFC(Remote Function Modules).
1. Expose the RFC as a SOAP Service using SOAP Manager and create Data Models on Eclipse IDE with SAP OData Plugins
2. Create a Gateway Service Project on Netweaver Gateway and import the service into your Eclipse IDE with SAP OData Plugins.
For method 2, the pre-requisite is to have an SAP Netweaver Gateway installed either in an Central Hub Deployment or Embedded Deployment
Central Hub Deployment of SAP Netweaver Gateway has SAP NW Gateway Server installed in a different instance then the SAP ERP instance whereas Embedded Deployment has all the components of SAP Netweaver Gateway installed in the same instance.
For this blog post we are going to follow method 2 and are using an Embedded Deployment model of SAP Netweaver Gateway.
Log in to you SAP Server Instance and go the the transaction SEGW
(If you are missing any roles, capture the SU53 logs and get in touch with your basis person to provide you with the required authorization. The basic authorization required would be of the Gateway Developer Role)
Once you log in to SEGW you would see the below screen
Click on the Create Button to create a new Project.
It will prompt you to enter the Project name, Description and the Package name if you wish to Transport the project to QAS. Else you can just create it
inside the Local Temp ($TMP) Directory by clicking Local Object button
Now we will create a Data Model Directly from the RFC,
I have an RFC made by name Z_SMP_PM_NOTIFICATION
which has two input parameters and returns a list as an output
So inside our project Right Click on Data Model and click on Import --> RFC/BOR Interface
Give the name of the Entity and the Destination RFC.
Here we will give the name of the Entity as NotificationList and the destination RFC as Z_SMP_PM_NOTIFICATION.
Click on Next to define the Fields that we require in our entity. For my RFC to work i need the REQ_INTERFACE_NAME as the input as the LT_NOTIF_LIST as output parameter so i would select only those fields.
Click on Next to define a key. You can also change the name of the fields under the name column. Defining a key for an entity is mandatory
Click on Finish to create the entity.
Next we will create an EntitySet which will be of the datatype the Entity that we created.
Double Click on the Entity Sets node and click on the Create Icon
to create a new entity. Give the name of the Entity Set and the Entity Type name as the name of the Entity that we just created
Once this is done you would see an entry under the Service Implementation node with the same name as the Entity Set.
Expand it to see you will see 5 operations along with every entity set
Create - This operation will be used if you want to create any data within SAP from the webservice. for e.g Creating a new Employee in the master table
Delete - This operation is used to delete existing entry within SAP from the webservice. for eg Deleting a particular Employee within the master table
GetEntity(Read) - This operation is used if you want to retrieve a single record against a key from SAP for e.g Retrieving details of a particular employee
GetEntitySet(Query) - This operation is used to retrieve a list of records from SAP against a query or without a queryfor e.g Retrieving list of employees or retrieving a list of employees with Country Code IN etc
Update - This operation is used to update the existing data of a record within SAP For e.g Updating contact details of a particular employee.
Since for this example our RFC returns a list of Notifications so we will proceed for defining a GetEntitySet(Query) Operation on our EntitySet.
Right Click on the GetEntitySet(Query) node and select Map to Datasource.
You can either map the fields manually or click on Propose Mapping button on the top to map it automatically
If your input parameter has any constant value then you can directly define it over here with ' ' quotes.
Once this is done we are done with the development of the Entity set and Mapping. Next this is we will Generate the Runtime Objects which all the Gateway Services require for operating.
Gateway Services based on Model Provider and Data Provider Classes.
Click on the Generate Runtime Objects button 
If there are not errors you will see a below message that all these classes are created with a green box on their side.
Once all the classes are made, next thing we will do is to register this service against the SAP Netweaver Gateway Server so that we can access it.
The pre requisite for this would be that you create Destination for the Systems. If the destinations are not maintained you can make those using the TCODE SM59 and then create an alias using SPRO->SAP Netweaver-->Gateway-->OData Channel-->Configuration-->ConnectionSettings-->SAP Netweaver Gateway to SAP System--> Manage SAP System Alias and create a new Entry there against the RFC Destination.
Double Click on the Service Maintenance Node and you should see all the Destinations that you have created.
Select the Destination and click on Register Service.
Click on Register Button and it will ask you for a prompt
It will open a new page, Do not change any values, Within the package Assignment give the Package name if you wish to transport or
you can store it as a Local Object.
Click on the green tick to register the service.
Once the service is registered and deployed you will see a green box against the destination.
We have now deployed the service on the SAP Netweaver Gateway Server.
Next we will proceed to testing the Service that we just deployed. Go to the transaction /IWFND/MAINT_SERVICE
Here you will see a list of services
Select our service and click on the Gateway Client button
It will open up a new window
click on the 
and you will see the list of Entity Sets that we created under this Service
If you have any input parameters then you can give it after the Entity Set name. The RFC that we created had one input parameter which was a constant so i defined the constant value during mapping itself. If you have any input values for query operation you can supply it as follows
/sap/opu/odata/sap/ZTESTNOTIFICATION_SRV/NotificationCollection?$filter=parametername eq 'value'
Once you add this click on the 
button to test the service.
It should return with a HTTP Request code 200 and with the data
This way you can develop multiple entity sets and test it.
Hope this helps you all.
For more info on SMP, follow SMP Developer Center
Thanks,
Rakshit Doshi