This page describes the steps for calling a web service using the REST protocol. This page also gives you background information on how web services work within the Blueriq architecture. There are two possibilities in Blueriq to define the data that is send to and from REST services. The first possibility is by using an XSD, and this works similar as in Chapter 4 - Calling a SOAP service. The second possibility is to define a domain schema.
The following steps have to be done, you can choose between two different first steps:
1. Using an XSD
This method can only be used for communicating with web services that send XML responses. If a different format such as JSON is required, you should use a domain schema.
Importing
In order to interpret an XML response from a REST web service, Blueriq needs to import an XSD. In contrast to SOAP, there may not be an explicit contract available for REST. You can use the API of the REST service to get XSD files.
If the REST service only gives example answers, you can generate an XSD file from the examples (see for instance http://www.freeformatter.com/xsd-generator.html).
Close your project and go to File → Import → Import XSD and provide the location of the XSD file. If you have multiple files (for example: your XSD is importing/including an XSD schema), provide a zip file with all needed files. This is essentially the same as importing a WSDL (Chapter 4 - Calling a SOAP service). Select the project for the import and you can choose whether to create a new module, or overwrite an existing one. The option 'Generate Domain' will automatically generate a domain model for you, based on the XSD schema. When this button is checked, entities, attributes and relations are created based on the type definitions in the XSD. When using an existing module, there may already be a domain model present, that uses identical names as in the XSD. When overwriting, conflicting elements are not created. Obviously, these problems do not occur if you use a new module. When 'Generate Domain' is unchecked, no domain model is generated for you. In that case, you can later match the elements from the XSD to you own domain (explained later). In general, it is advised to use a separate module in order not to mix the domain model for the web service with the domain of your business.
You should get the message that the import was successful.
Mapping with Domain Model
Open your project and go the module which contains the web service. The module now has a Schema Set. This item can be found in the bar on the left side of the screen, as can be seen below.
The Schema Set defines which entities, attributes and relations are used by the web service (they map the XSD to the domain model). This works exactly the same for REST and SOAP, and the description can be found here: Chapter 4 - Calling a SOAP service.
1. Using a domain schema
In Blueriq version 9.2.6 we added a new element, the domain schema. This domain schema lets you define a representation of your domain that is used for the communication with a web service. In the below example, it is chosen that the status of an airport is represented by a certain set of attributes, starting with the delay. An important point to notice is that the domain schema is independent of the language that is used for the communication, and projects can add implementations of any representation not covered out of the box (JSON, XML). The domain schema that you define in studio is used as basis to create a message to a web service or to read a message from a web service. The domain schema can be translated to JSON or XML in a straightforward way, and can be inspected with the preview button.
You can see the domain schema as a sort of contract of the communication. You start with an entity that represents the begin and the end of the message. For every attribute/relation you can select a name, what datatype it is, if it is required within the message and if it is multivalued. This contract should be set up to reflect the message that is send, but it can be different to the internal Blueriq domain. For instance, your contract uses a multivalued attribute. Your application always has one value for this attribute however, so it is not multivalued. When sending a message, it is no problem to insert a single-valued attribute in a multivalued entry in the domain schema. It will just be send as a list with only one entry. You have to be careful if it is the other way around, storing a list with possibly more values on a single values attribute.
2. Defining the REST service
In contrast to importing a WSDL, no service definition is automatically generated. You have to define how the REST service is called manually. Create a new REST service object and give your REST service a name.
Next, you need to specify the location of the REST service. This is an URL. You can already specify fragments and arguments here, but then you cannot change them later. For example, check http://services.faa.gov/airport/status/IAD?format=xml. In this case, airport, status and IAD are dynamic fragments and can change, depending on input by the user. You would only use http://services.faa.gov/ as location in this case.
Now you specify how the communication is specified. This can either be a domain schema, or an XSD schema set. You have to choose one XSD schema set here that has to include everything for the entire web service. In contrast, by choosing a domain schema, you will choose later what domain schema to use for every separate method.
You can specify as many operations as you need, by pressing on the plus icon. Give every operation a unique name.
Request
If you want to dynamically change the address or send custom headers or body in your message, you need to specify a singleton entity from where the information is gathered (1). (2) shows the URL you are going to call. Items within {} are dynamic and determined at runtime. You can add static fragments (3) which are always the same, or dynamic fragments (4) which are filled by attributes of the request entity. You can specify arguments (5) of your request the same way. There are 4 different HTTP methods: GET, POST, PUT and DELETE. Most likely, the web service works with the GET method. This method does not alter the state of the web service and just asks for information. At (6) you specify what method to use.
You can also send a message to the REST web service as part of the HTTP headers. This happens more often with POST and PUT methods. This procedure is the same as for the response of the message that you find just below here.
Response
Now you can specify how your response message looks like. If you need to set headers, then you can do so at (1) in the same way you set arguments or fragments for the request. If you need to send information in the body of the message, for example with a POST message, then you can specify this now. This screen looks different depending on if you send information using an XSD schema set or a domain schema.
We explain the XSD schema set first. If you have a SimpleType in the schema, then you fill in an attribute at (4). If it is a complexType, then first choose which entity will be sent at (2) and then your attribute field (4) will switch to a relation field. Fill in the name of the relation between your singleton response entity and your data entity. Custom Schema Elements (3) are ways to fill in your schema in a different way other than with data from your profile. It is not needed at the moment (An example is a justification tree)
When using a domain schema, you now simply select the domain schema that you want to use to send information (2). Furthermore, you have to select a body relation (3). This is a relation between the singleton response entity of your message and the entity that is chosen as the root entity in your domain schema.
3. Creating a Service Call
In order to call a REST web service, you create a service call of type AQ_WebServiceClient the same way as for SOAP web services (Chapter 4 - Calling a SOAP service). The only difference is that you select REST at the service dropdown. You usually do not want to supply a URL, as it will overwrite the dynamic URL generation of the REST service definition.
4. Using the Webservice
This is similar to SOAP (Chapter 4 - Calling a SOAP service).
Usually you want to use a separate module for your web service. Read more information on this here: Chapter 7 - Modules and Datamapping
Previous Chapter: Chapter 4 - Calling a SOAP service
Next Chapter: Chapter 6 - Setting up Blueriq as a web service
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