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In the ESB profile of WSO2 Enterprise Integrator (WSO2 EI), this is commonly referred to as Service Chaining, where several services are integrated based on some business logic and exposed as a single, aggregated service. 

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Let's create HTTP endpoints to the back-end services that you need to connect, in order to check the channeling fee and to settle payment.

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1. In EI Tooling, add a Property mediator just after the Get Hospital Property mediator in the In sequence of the API resource to retrieve and store the card number that is sent in the request payload.

    

   With the Property mediator selected, access the Properties tab and fill in the information as in the following table:

   Field	Value
   Property Name	Select New Property
   New Property Name	card_number
   Property Action	Select set
   Value Type	Select Expression
   Value Expression	json-eval($.cardNo)
   Description	Get Card Number

   Tip
   For detailed instructions on adding a Property mediator, see Mediating requests to the back-end service.

2. Go to the first case box of the Switch mediator. Add a Property mediator just after the Log mediator to store the value for uri.var.hospital variable that will be used when sending requests to ChannelingFeeEP.
   

   With the Property mediator selected, access the Properties tab and fill in the information as in the following table:

   Field	Value
   Property Name	Select New Property
   New Property Name	uri.var.hospital
   Property Action	Select set
   Value Type	Select LITERAL
   Property Data Type	Select STRING
   Value	grandoaks
   Description	Set Hospital Variable

3. Similarly, add property mediators in the other two case boxes in the Switch mediator. Change only the Value field as follows:
   • Case 2: clemency
   • Case 3: pinevalley
     

4. Delete the Send mediator by right clicking on the mediator and selecting Delete from Model. Replace this with a Call mediator from the Mediators palette and add GrandOakEP from the Defined Endpoints palette to the empty box adjoining the Call mediator. 
   
   Replace the Send mediators in the following two case boxes as well and add ClemencyEP and PineValleyEP to the respective boxes adjoining the Call mediators.
   

   Info
   Replacing with a Call mediator allows us to define other service invocations following this mediator.

   Let's use Property mediators to retrieve and store the values that you get from the response you receive from GrandOakEP, ClemencyEP or PineValleyEP.

5. Next to the Call mediator box, add a Property mediator to retrieve and store the value sent as appointmentNumber.

   

   With the Property mediator selected, access the Properties tab and fill in the information as in the following table:

   Field	Value
   Property Name	Select New Property
   New Property Name	uri.var.appointment_id (This value is used when invoking ChannelingFeeEP)
   Property Action	Select set
   Value Type	Select EXPRESSION
   Value Expression	json-eval($.appointmentNumber)
   Description	Get Appointment Number

   Note

   You derive the Value Expression in the above table from the following response that is received from GrandOakEP, ClemencyEP or PineValleyEP: Code Block {"appointmentNumber":1, "doctor": {"name":"thomas collins", "hospital":"grand oak community hospital", "category":"surgery","availability":"9.00 a.m - 11.00 a.m", "fee":7000.0}, "patient": {"name":"John Doe", "dob":"1990-03-19", "ssn":"234-23-525", "address":"California", "phone":"8770586755", "email":"johndoe@gmail.com"}, "fee":7000.0, "confirmed":false}

6. Similarly, add two more Property mediators as follows. They retrieve and store the doctor details and patient details respectively, from the response that is received from GrandOakEP, ClemencyEP or PineValleyEP.

   Field	Value
   Property Name	Select New Property
   New Property Name	doctor_details
   Property Action	Select set
   Value Type	Select EXPRESSION
   Value Expression	json-eval($.doctor)
   Description	Get Doctor Details
   Property Name	Select New Property
   New Property Name	patient_details
   Property Action	Select set
   Value Type	Select EXPRESSION
   Value Expression	json-eval($.patient)
   Description	Get Patient Details

   
   

   

7. Add a Call mediator and add ChannelingFeeEP from Defined Endpoints palette to the empty box adjoining the Call mediator. 

8. Add a Property mediator adjoining the Call mediator box to retrieve and store the value sent as actualFee. Access the Properties Property tab of the mediator and fill in the information as in the following table:

   Field	Value
   Property Name	Select New Property
   New Property Name	actual_fee (This value is used when invoking SettlePaymentEP )
   Property Action	Select set
   Value Type	Select EXPRESSION
   Value Expression	json-eval($.actualFee)
   Description	Get Actual Fee

   Note
   You derive the Value Expression in the above table from the following response that is received from ChannelingFeeEP: Code Block {"patientName":" John Doe ", "doctorName":"thomas collins", "actualFee":"7000.0"}

   Let's use the PayloadFactory mediator to construct the following message payload for the request sent to SettlePaymentEP. 

   Code Block

   {"appointmentNumber":2, "Doctordoctor":{ "name":"thomas collins", "hospital":"grand oak community hospital", "category":"surgery", "availability":"9.00 a.m - 11.00 a.m", "Fee":7000.0 }, "Patientpatient":{ "name":"John Doe", "Dob":"1990-03-19", "ssn":"234-23-525", "address":"California", "phone":"8770586755", "email":"johndoe@gmail.com" }, "Feefee":7000.0, "Confirmedconfirmed":false, "card_number":"1234567890" }

9. Next to the Property mediator, add a PayloadFactory mediator from the mediators palette to construct the above message payload. 

   

   With the Payloadfactory mediator selected, access the properties tab of the mediator and fill in the information as in the following table:

   Field	Value	Description
   Payload Format	Select Inline	-
   Media Type	Select json	-
   Payload	{ "appointmentNumber":$1, "doctor":$2, "patient":$3, "fee":$4, "confirmed":"false", "card_number":"$5" }	The message payload to send with the request to SettlePaymentEP. In this payload, $1, $2, $3, $4 and $5 indicate variables.

   We will look at adding the value for the field Args in the following steps.

   Tip
   To avoid getting an error message, first select the Media Type before providing the Payload.

10. To add the Args field for the PayloadFactory mediator, click the Browse (...) icon in the Args field. Click on the Add button and enter the following information as in the table below. It provides the argument that defines the actual value of the first variable used in the format definition in the previous step.

    Field	Value	Description
    Type	Select Expression	-
    Value	$ctx:uri.var.appointment_id	The value for the first variable ($1) in the message payload format.
    Evaluator	Select xml	Indicates that the expression provided is in XML.

    Info
    The $ctx method is similar to using the get-property method. This method checks in the message context. For more details on using this method, refer the documentation.

11. Similarly, click Add and add more arguments to define the other variables that are used in the message payload format definition. Use the following as the Value for each of them: 

    $ctx:doctor_details
$ctx:patient_details
$ctx:actual_fee
$ctx:card_number
    

12. Add a Call mediator and add SettlePaymentEP from Defined Endpoints palette to the empty box adjoining the Call mediator.
13. Add a Respond mediator to send the response to the client. 
    
    You should now have a completed configuration that looks like this:
    
14. Save the updated REST API configuration.

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Since you created new endpoints, these will need to be packaged into our existing C-App. 

Package the C-App names SampleServicesCompositeApplication project with the artifacts created. 

Starting the

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ESB runtime and deploying the artifacts

On the Servers tab, expand the WSO2 Carbon server, right-click SampleServicesCompositeApplication, and choose Redeploy. The Console window will indicate that the C-App has been deployed successfully.

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The Healthcare service is now active and you can start sending requests to the service.

Sending requests to

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the ESB

1. Create a JSON file names request.json with the following request payload.

   Code Block
   { "name": "John Doe", "dob": "1940-03-19", "ssn": "234-23-525", "address": "California", "phone": "8770586755", "email": "johndoe@gmail.com", "doctor": "thomas collins", "hospital": "grand oak community hospital", "cardNo": "7844481124110331", "appointment_date": "2017-04-02" }

2. Open a command line terminal and execute the following command from the location where request.json file you created is saved:
   

   curl -v -X POST --data @request.json http://localhost:8280/healthcare/categories/surgery/reserve --header "Content-Type:application/json"

   Info
   This is derived from the URI-Template defined when creating the API resource. http://<host>:<port>/categories/{category}/reserve

   You will see the response as follows:

   Code Block
   {"patient":"John Doe", "actualFee":7000.0, "discount":20, "discounted":5600.0, "paymentID":"e2781025-5332-4a78-950b-3be83c99fa76", "status":"Settled"}

You have now explored how the ESB profile of WSO2 EI can do service chaining using the Call mediator and transform message payloads from one format to another using the PayloadFactory mediator.