Exposing Data in JSON Format

You can send and receive JSON messages by default via WSO2 Micro Integrator. See the topics given below to understand how data can be exposed in the JSON format, and how data can be changed by sending JSON payloads. In this example, you will use a data service that exposes RDBMS data.

A data service can expose data in one of the following formats: XML, RDF, or JSON. You can select the required format by specifying the output type for the data service query. To expose data in JSON, you need to select JSON as the output type, and map the output to a JSON template.

Prerequisites

Let's create a MySQL database with the required data.

  1. Install the MySQL server.

  2. Create a database named Employees.

    CREATE DATABASE Employees;

  3. Create the Employee table inside the Employees database:

    USE Employees;

CREATE TABLE Employees (EmployeeNumber int(11) NOT NULL, FirstName varchar(255) NOT NULL, LastName varchar(255) DEFAULT NULL, Email varchar(255) DEFAULT NULL, Salary varchar(255));

Synapse configuration

Given below is the data service configuration you need to build. See the instructions on how to build and run this example.

<data name="RDBMSDataService" serviceStatus="active" transports="http https local">
   <config enableOData="false" id="Datasource">
      <property name="driverClassName">com.mysql.jdbc.Driver</property>
      <property name="url">jdbc:mysql://localhost:3306/Employees</property>
      <property name="username">root</property>
      <property name="password">password</property>
   </config>
   <query id="GetEmployeeDetails" useConfig="Datasource">
      <sql>select EmployeeNumber, FirstName, LastName, Email, Salary from Employees where EmployeeNumber=:EmployeeNumber</sql>
      <result outputType="json">{
   "Employees":{
      "Employee":[
         {
            "EmployeeNumber":"$EmployeeNumber",
            "FirstName":"$FirstName",
            "LastName":"$LastName",
            "Email":"$Email",
            "Salary":"$Salary"
         }
      ]
   }
}</result>
      <param name="EmployeeNumber" sqlType="STRING"/>
   </query>
   <query id="AddEmployeeDetails" useConfig="Datasource">
      <sql>insert into Employees (EmployeeNumber, FirstName, LastName, Email, Salary) values(:EmployeeNumber,:FirstName,:LastName,:Email,:Salary)</sql>
      <param name="EmployeeNumber" sqlType="STRING"/>
      <param name="FirstName" sqlType="STRING"/>
      <param name="LastName" sqlType="STRING"/>
      <param name="Email" sqlType="STRING"/>
      <param name="Salary" sqlType="STRING"/>
   </query>
   <query id="UpdateEmployeeDetails" useConfig="Datasource">
      <sql>update Employees set LastName=:LastName, FirstName=:FirstName, Email=:Email, Salary=:Salary where EmployeeNumber=:EmployeeNumber</sql>
      <param name="LastName" sqlType="STRING"/>
      <param name="FirstName" sqlType="STRING"/>
      <param name="Email" sqlType="STRING"/>
      <param name="Salary" sqlType="STRING"/>
      <param name="EmployeeNumber" sqlType="STRING"/>
   </query>
   <operation name="GetEmployeeOp">
      <call-query href="GetEmployeeDetails">
         <with-param name="EmployeeNumber" query-param="EmployeeNumber"/>
      </call-query>
   </operation>
   <operation name="AddEmployeeOp">
      <call-query href="AddEmployeeDetails">
         <with-param name="EmployeeNumber" query-param="EmployeeNumber"/>
         <with-param name="FirstName" query-param="FirstName"/>
         <with-param name="LastName" query-param="LastName"/>
         <with-param name="Email" query-param="Email"/>
         <with-param name="Salary" query-param="Salary"/>
      </call-query>
   </operation>
   <operation name="UpdateEmployeeOp">
      <call-query href="UpdateEmployeeDetails">
         <with-param name="LastName" query-param="LastName"/>
         <with-param name="FirstName" query-param="FirstName"/>
         <with-param name="Email" query-param="Email"/>
         <with-param name="Salary" query-param="Salary"/>
         <with-param name="EmployeeNumber" query-param="EmployeeNumber"/>
      </call-query>
   </operation>
   <resource method="GET" path="Employee/{EmployeeNumber}">
      <call-query href="GetEmployeeDetails">
         <with-param name="EmployeeNumber" query-param="EmployeeNumber"/>
      </call-query>
   </resource>
   <resource method="POST" path="Employee">
      <call-query href="AddEmployeeDetails">
         <with-param name="EmployeeNumber" query-param="EmployeeNumber"/>
         <with-param name="FirstName" query-param="FirstName"/>
         <with-param name="LastName" query-param="LastName"/>
         <with-param name="Email" query-param="Email"/>
         <with-param name="Salary" query-param="Salary"/>
      </call-query>
   </resource>
   <resource method="PUT" path="Employee">
      <call-query href="UpdateEmployeeDetails">
         <with-param name="LastName" query-param="LastName"/>
         <with-param name="FirstName" query-param="FirstName"/>
         <with-param name="Email" query-param="Email"/>
         <with-param name="Salary" query-param="Salary"/>
         <with-param name="EmployeeNumber" query-param="EmployeeNumber"/>
      </call-query>
   </resource>
</data>

Alternatively, you can use one of the following JSON templates for the response mapping:

  • Simple JSON template

    { "Employees":
      {"Employee":[
        {"EmployeeNumber":"$EmployeeNumber",                       
         "Details": {
          "FirstName":"$FirstName",
          "LastName":"$LastName",
          "Email":"$Email",
          "Salary":"$Salary"
         }
        }                 
      ]
    }           
}

  • Define data types

    In a basic JSON output mapping, we specify the field values that we expect in the query result. You can give additional properties to this field mapping such as data type of the field, the possible content filtering user roles etc. These extended properties for the fields are given in parentheses, with a list of string tokens providing the additional properties, separated by a semicolon (";"). See the sample below.

Info

As shown in the sample given above, the column name values that are expected in the query result should be referred to by the column name with the $ prefix. E.g. $EmployeeNumber.

Also, the structure of the JSON template should follow some guidelines in order to be compatible with the result. These guidelines are:

  • The top most item should be a JSON object. It cannot be a JSON array.
  • For handling multiple records from the result set, the immediate child of the top most object can be a JSON array, and the array should contain only a single object.
  • If only a single result is returned, the immediate child of the top most object can be a single JSON object.
  • After the immediate child of the top most object, there cannot be other JSON arrays in the mapping.

All JSON responses are returned as an array.

  • If you want to write a nested query using JSON, see the example on nested queries.

Build and run

Create the artifacts:

  1. Set up WSO2 Integration Studio. The path to this folder is referred to as MI_TOOLING_HOME throughout this tutorial.

  2. Download the JDBC driver for MySQL from here and copy it to the MI_TOOLING_HOME/Contents/Eclipse/runtime/microesb/lib/ (for MacOS) or MI_TOOLING_HOME/runtime/microesb/lib/ (for Windows) directory.

    Note

    If the driver class does not exist in the relevant folders when you create the datasource, you will get an exception such as Cannot load JDBC driver class com.mysql.jdbc.Driver.

  3. Create a Data Service project.

  4. Create the data service with the configurations given above.
  5. Deploy the artifacts in your Micro Integrator.

GET data in JSON

The RDBMSDataService that you are using contains the following resource:

  • Resource Path: Employee/{EmployeeNumber}
  • Resource Method: GET
  • Query ID: GetEmployeeDetails

You can now RESTfully invoke the above resource. To send a JSON message to a RESTful resource, you can simply add the “ Accept : Application/json ” to the request header when you send the request. The service can be invoked in REST-style via curl .
Shown below is the curl command to invoke the GET resource:

curl -X GET -H "Accept: application/json" http://localhost:8290/services/RDBMSDataService/Employee/{EmployeeNumber}

Example:

curl -X GET -H "Accept: application/json" http://localhost:8290/services/RDBMSDataService/Employee/1

As a result, you receive the response in JSON format as shown below.

{"Employees":{"Employee":[{"EmployeeNumber":"1","FirstName":"John","LastName":"Doe","Email":"[email protected]","Salary":"10000"},{"EmployeeNumber":"1","FirstName":"John","LastName":"Doe","Email":"[email protected]","Salary":"20000"}]}

POST/UPDATE data using JSON

When a client sends a request to change data (POST/PUT/DELETE) in the datasource, the HTTP header Accept should be set to application/json .  Also, if the data is sent as a JSON payload, the HTTP header Content-Type should be set to application/json .

The RDBMSDataService that you are using contains the following resources for adding and updating data.

  • Resource for adding employee information:

    • Resource Path: Employee
    • Resource Method: POST
    • Query ID: AddEmployeeDetails

  • Resource for updating employee information:

    • Resource Path: Employee
    • Resource Method: PUT
    • Query ID: UpdateEmployeeDetails

You can RESTfully invoke the above resource by sending HTTP requests as explained below.

Post data

To post new employee information, you need to invoke the resource with the POST method.

  1. First, create a file named employee-payload.json , and define the JSON payload for posting new data as shown below.

    {
  "user_defined_value": {
    "EmployeeNumber" : "14001",
    "LastName": "Smith",
    "FirstName": "Will",
    "Email": "[email protected]",
    "Salary": "15500.0"
  }
}

  2. On the terminal, navigate to the location where the employee-payload.json file is stored, and execute the following HTTP request:

    curl -X POST -H 'Accept: application/json'  -H 'Content-Type: application/json' --data "@employee-payload.json" -k -v http://localhost:8290/services/RDBMSDataService/Employee

Post data in batches

You are able to post JSON data in batches using the RDBMSDataService that you created or uploaded.

Info

Verify that batch requesting is enabled for the data service.

  1. First, create a file named employee-batch-payload.json , and define the JSON payload for posting multiple employee records (batch) as shown below.

    {
    "user_defined_value": {
        "user_defined_value": [
            {
                "EmployeeNumber": "5012",
                "FirstName": "Will",
                "LastName": "Smith",
                "Email": "[email protected]",
                "Salary": "13500.0"
            },
            {
                "EmployeeNumber": "5013",
                "FirstName": "Parker",
                "LastName": "Peter",
                "Email": "[email protected]",
                "Salary": "15500.0"
            }
        ]
    }
}

  2. On the terminal, navigate to the location where the employee-batch-payload.json file is stored, and execute the following HTTP request:

    curl -X POST -H 'Accept: application/json'  -H 'Content-Type: application/json' --data "@employee-batch-payload.json" -k -v http://localhost:8290/services/RDBMSDataService/Employee_batch_req

Update data

To update the existing employee records, you need to invoke the resource with the PUT method.

  1. First, create a file named employee-upload-update.json , and define the JSON payload for updating an existing employee record as shown below.
    For example, change the salary amount. Make sure that the employee number already exists in the database.

    {
  "user_defined_value": {
    "EmployeeNumber" : "1",
    "FirstName": "Will",
    "LastName": "Smith",
    "Email": "[email protected]",
    "Salary": "78500.0"
  }
}

  2. On the terminal, navigate to the location where the employee-upload-update.json file is stored, and execute the following HTTP request:

    curl -X PUT -H 'Accept: application/json'  -H 'Content-Type: application/json' --data "@employee-upload-update.json" -k -v http://localhost:8290/services/RDBMSDataService/Employee

Post data using Request Box

When the Request Box feature is enabled, you can invoke multiple operations (consecutively) using one single operation. The process of posting a JSON payload through a request box transaction is explained below.

Info

Verify that batch requesting is enabled for the data service.

  1. First, create a file named employee-request-box-payload .json , and define the JSON payload for posting multiple employee records (batch) as shown below.

    Tip

    The following payload works for this use case. When you create payloads for different use cases, be mindful of the tips given here .

    {
 "request_box"  : { 
      "_postemployee" : {
                "EmployeeNumber"  : "14005", 
                "LastName" :  "Smith" ,
                "FirstName" :  "Will" , 
                "Email" :  "[email protected]" ,
                "Salary" : "15500.0"
                        },
      "_getemployee_employeenumber":{
                "EmployeeNumber"  : "14005"
           }
    }
}

  2. On the terminal, navigate to the location where the employee-request-box-payload.json file is stored, and execute the following HTTP request:

    curl -X POST -H 'Accept: application/json'  -H 'Content-Type: application/json' --data "@employee-request-box-payload.json" http://localhost:8290/services/RDBMSDataService/request_box

Tip

Creating JSON payloads for Request Box transactions

Note the following when you define a JSON payload for a request box transaction: The object name specified in the payload must be in the following format: " _<HTTP_METHOD><RESOURCE_PATH> " where RESOURCE_PATH represents the path value specified in the data service resource. For example, if the RESOURCE_PATH is "employee", the payload object name should be as follows:

  • For HTTP POST requests: _postemployee
  • For HTTP PUT requests: _putemployee

The child name/values of the child fields in the payload should be the names and values of the input parameters in the target query.

Handling a resource path with the "/" symbol

If the RESOURCE_PATH specified in the data service contains the "/" symbol, be sure to replace the "/" symbol with the underscore symbol ("\") in the payload object name.

Important! In this scenario, the RESOURCE_PATH value should only contain simple letters. For example, the value can be " /employee/add" but not " /Employee/Add".

For example, if the RESOURCE_PATH is /employee/add , the payload object name should be as follows:

  • For HTTP POST requests: _post_employee_add
  • For HTTP PUT requests: _put_employee_add
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