Consume a REST Service (for Versions 6.0–6.10)

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1 Introduction

With the REST services module from the Mendix App Store, the full power of JSON-based REST APIs is available to Mendix developers. The module serves three goals: to consume services, publish services, and synchronize data between (Mendix) apps by combining consuming and publishing.

In this how-to, you will consume a JSON-based REST services by integrating with the API of the world famous Rijksmuseum that allows us to search for art.

This how-to will teach you how to do the following:

  • Create a GET REST Service
  • Create a POST REST Service

2 Prerequisites

In this section you will download the REST module from the App Store and test your service in the browser. The service tested in this how-to is the API of the Rijksmuseum, used to search for art. You will be consuming this endpoint: https://www.rijksmuseum.nl/api/en/collection/?key=<key>&format=json&q=<search query>.

To use this service, you need to create an account at https://www.rijksmuseum.nl in order to obtain an API key at the website. You can also perform the steps of this how-to using your own REST service.

Make sure you have completed these prerequisite steps:

  1. Open the Mendix Modeler, and then click App Store in the upper-right part of the toolbar to open the App Store.
  2. In the App Store, search for and download the latest Rest Services module:
  3. Search for and download the latest Community Commons Function Library module from the App Store:
  4. Test your service in the browser by filling in the <key> and <search query> fields in the URL stated above (you can use Van Gogh as an example search query). This will result in something similar to the following JSON fragment:

3 Creating a Data Model for the REST Service

In this section, you will define a data model to consume this service. You will create a Query entity to store the search request and a Results object to store the result. Then you will add all the interesting pieces of the resulting JSON to your domain model so that it reflects the structure of the JSON response (according to the JSON deserialization rules described here: https://github.com/mweststrate/RESTServices#json-deserialization).

  • { = object

  • [{ = list of objects

  • [ = list (to be able to map a list of string/float/Boolean values, you need to set a many-to-many association to the Primitive entity in your RestServices module or to a subclass of the Primitive entity)

To create a data model for the REST service, follow these steps:

  1. Create a non-persistable Query object and name the attribute the same as the query parameter (case-sensitive):
  2. Create a non-persistable Results object to store the result and link it to the Query entity in order to display the results in the interface: Create your entity structure based on the JSON structure, starting with the Results entity. Make sure you rename the association to the name of the JSON object.

  3. Create a non-persistable entity called ArtObject with two attributes:

    • title
    • principalOrFirstMaker
  4. Create a many-to-many (*-*) association between the Results entity and the ArtObject entity.

  5. Rename the association to artObjects:

  6. Create a non-persistable entity called Image with one attribute called url (string).

  7. Create a one-to-many (1-*) association between the ArtObject entity and the Image entity and call it webImage:

  8. Create a non-persistable entity called ProductionPlace.

  9. Make a generalization to RestServices.Primitive.

  10. Create a many-to-many (*-*) association between the ArtObject entity and the ProductionPlace entity and call it productionPlaces:

Your Domain Model should look similar to this:

Section Description
A List of objects, association: artObjects
B The title attribute of the ArtObject entity (you can name the entity anything you want, but the attribute has to be exactly the same)
C Single object, association: headerImage
D List of strings, association: productionPlaces

4 Creating the Results Page

In this section, you will create a page enabling users to enter a search query and see the results in a data grid over the provided association, and you will add a button that will execute the search.

4.1 Using a Microflow as a Data Source

To use a microflow as a data source, follow these steps:

  1. Create a new page called SearchArt.
  2. Add a data view with the Microflow data source type, and then click Select….
  3. Create a new microflow and call it DS_NewSearchQuery.
  4. Add a Create object activity.
  5. Select the Query entity from the Select Entity pop-up window:
  6. Name the query NewQuery in the Create Object dialog box, and click OK.
  7. Open the properties of the end event and select Object for Type:
  8. Select the Query entity, and under Return value, enter $NewQuery:
  9. Click OK and then save the microflow.

4.2 Creating the Search and Result Pages

To create the search and result pages, follow these steps:

  1. Go back to the SearchArt page and add a Group Box.
  2. Add a new Table with three columns.
  3. In the first column, enter Search the Rijksmuseum.
  4. Add the Query > q attribute to the middle column.
  5. Add a microflow button to the last column:
  6. Add a nested Results data view inside the Query data view, and then add a nested ArtObject template grid inside the Results data view:
  7. Add the fields as illustrated in the screenshot below to the ArtObject template grid:

    You can download the Image Viewer widget from the App Store and add the url attribute to the Image attribute in the properties section:

  8. Add the created page to your navigation.

5 Consuming the Service Using a Get Request

In this section you will consume the service in the Search microflow using the Get request to retrieve data.

To consume the service using a Get request, follow these steps:

  1. Create a microflow with Query as the input parameter and link it to the Search button:
  2. Create a new Results object and add a request Java Action to the microflow:
  3. Add the request Java Action with the following details:

    Name Argument
    method RestServices.HttpMethod.GET
    url https://www.rijksmuseum.nl/api/en/collection/?key=' + + ‘&format=json’
    optRequestData $Query
    optResponseData $newResults
    sendWithFormEncoding false

    You have now requested the data from the Rijksmuseum, and the data has been mapped to your Results and associated entities.

  4. Add a Change object activity and link the NewResults object to the Query object. This will show the search results on the page:

  5. Run your application and search for van Gogh. You will see the following results:

6 Consuming the REST Service with a POST Request

In this section, you will create a microflow to hypothetically send data back to the Rijksmuseum. There is no POST service available, but this example demonstrates how you would setup a POST request if the service was available.

  1. Open the SearchArt page.
  2. Add a microflow button to the search page and name it Update.
  3. Add an edit button to the ArtObject template grid so that you can change the data of the result.
  4. Create a microflow for the Update button and add the following:

    • Input Parameter –Results
    • Java action – Request
    Name Argument
    method RestServices.HttpMethod.POST
    url https://www.rijksmuseum.nl/api/en/collection/?key=' + + ‘&format=json’
    optRequestData $Results (ideally you would name it Request)
    optResponseData Add here the entity to which you can map the response (if a response is available from the service)
    sendWithFormEncoding false

    If you now change the data of one of the objects linked to the Results object that you are passing on to the microflow, the POST request will update the other system accordingly.

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