Create a web service module

Resources are identified as a set of functions within the Web services module that provides the service.

In this task you create a Genero BDL module and code two functions that define access to resources.

In the RESTful high-level framework you must define functions as PUBLIC in order to expose the resource.

A RESTful Web service function is a normal BDL function that uses attributes. These attributes (WS*) are defined specifically for high-level REST.

In the function attributes clause there is an attribute that determines the HTTP verb (for example, WSGet). The WSPath attribute determines the resource endpoint. These two attributes must be included in all RESTful Web service functions.

Other attributes are set in the ATTRIBUTES property of input and output parameters to define HTTP headers, etc.

Create your application module. For example, create a file named myservice.4gl.
Start with importing the com Web services module, and declare that you want to use the test1schema schema:
```
IMPORT com
SCHEMA test1schema
```
Define types used by the REST functions.
We define the following record type at the modular level:
```
TYPE custinfoType RECORD LIKE custinfo.*
```

Create a function to get all customer records (copy and paste the code below)

In the function's ATTRIBUTES clause the following attributes are set:

WSGet – specifies the GET HTTP verb.
WSPath – specifies the resource endpoint.
WSDescription – provides a description of the resource which will be displayed in the generated OpenAPI specification file.

In the function's RETURNS clause, we specify a DYNAMIC ARRAY OF custinfoType to return the complete set of customer records.

PUBLIC FUNCTION getCustomerRecords()
    ATTRIBUTES(WSGet,
        WSPath = "/customers",
        WSDescription = "Fetches all customer records.")
    RETURNS (DYNAMIC ARRAY OF custinfoType)
    DEFINE custlist DYNAMIC ARRAY OF custinfoType
    DEFINE i INTEGER = 1
    DECLARE customerCurs CURSOR FOR SELECT * FROM custinfo ORDER BY cust_lname
    FOREACH customerCurs INTO custlist[i].*
        LET i = i + 1
    END FOREACH
    # Remove the empty element implied by reference in FOREACH loop
    CALL custlist.deleteElement(custlist.getLength())
    RETURN custlist
END FUNCTION

Create a function to get a customer's details (copy and paste the code below)
In the function's ATTRIBUTES clause the following attributes are set:
- WSGet – specifies the GET HTTP verb.
- WSPath – specifies the resource endpoint. It includes a {WSParam-identifier} as a template path. The value will be specified in an input parameter with an WSParam attribute.
- WSDescription – provides a description of the resource which will be displayed in the generated OpenAPI specification file.
- WSThrows - specifies how we handle different outcomes of the request. We set these in the attribute with a standard HTTP status code and a message as follows:
  - 404:Not Found, if the resource is not found.
  - 400:SQL error, when an unexpected SQL error occurs.
  We trap errors in the TRY/CATCH block. We check the SQLCA record after the execution of the SQL query. The call to SetRestError() with NULL handles the return of the message defined in WSThrows.
In the function's input parameter we set the attribute WSParam as the part of the path to a specific customer resource. The customer id will be provided in the URI request, for example:
```
GET http://localhost:8090/MyService/customers/2
```
In the function's RETURNS clause we return the customer record in the fCustomerRec variable of type custinfoType.
```
PUBLIC FUNCTION getCustomerById(
    resourceId INTEGER ATTRIBUTES(WSParam))
    ATTRIBUTES(WSGet,
        WSPath = "/customers/{resourceId}",
        WSDescription = "Fetches a single record from the Customer resource.",
        WSThrows = "404:Not Found,400:SQL Error")
    RETURNS(custinfoType)
    DEFINE fCustomerRec custinfoType
    TRY
        SELECT custinfo.*
            INTO fCustomerRec.*
            FROM custinfo
            WHERE custinfo.cust_num = resourceId
        IF sqlca.sqlcode == NOTFOUND THEN
            # 404 is defined by the WSThrows attribute
            CALL com.WebServiceEngine.SetRestError(404, NULL)
        END IF
    CATCH
        DISPLAY "SQL error: ", sqlca.sqlcode
        CALL com.WebServiceEngine.SetRestError(400, NULL)
    END TRY
    RETURN fCustomerRec
END FUNCTION
```