Luke Stevens, Murdoch Childrens Research Institute https://www.mcri.edu.au 20-Jun-2017

Thanks to Mark Oium, Medical College of Wisconsin, Milwaukee, WI, for example of Stata shell command and curl to exchange data with REDCap via the API: https://community.projectredcap.org/articles/462/api-examples.html (not public)

API is an acronym of "Application Programming Interface", which in English translates as a mechanism via which you may interact with a system (in this case REDCap) from a program, rather than via the regular web-browser interface.

The Stata do-files included here give examples of how you can utilise the REDCap API to interact with a REDCap project from within Stata without having to log on to REDCap via your browser in order to download or upload data and/or metadata.

The documentation lists the "API methods" ("functions", if you like) that are available and how you can use them.

The REDCap API documentation is available from within the REDCap web application at https://redcap-url.your-institution.edu/api/help/

Logging on to REDCap and downloading data for further processing is a common task, whether for obtaining raw data for cleaning and analysis purposes, for preparing summary reports or CONSORT diagrams, or even for just taking a quick peek at some aspect of a project or its data.

Scripting an API call into your do-file could be a handy time-saver, but also enables you to perform your data downloads in a documented and repeatable manner. #reproducibleresearch

Note that using the API will not completely replace the browser interface. You may still wish to download REDCap's regular Stata do-files that contain labelling commands, for example.

Before you can follow the example do-files you need a REDCap project to access, an "API token", which functions as your username and password (keep it secret!) and also a copy of curl, the program that will enable you to communicate programmatically with your REDCap server.

You will need access to an instance of REDCap within which you can create new projects. Download the project XML file provided in this repository and upload it on REDCap's "Create New Project" page. You now have a new project you can use as you like for practice with the REDCap API.

You must never write down your REDCap password, and this prohibition extends to including passwords within program scripts (e.g. a do-file). In order to avoid having to record passwords this way it is common for APIs to authenticate users via a user-specific token - an unmemorable string of hexadecimal digits.

Follow these steps to obtain an API token:

1. Navigate to the User Rights page of your new practice project.

2. Click on your username and then "Edit user privileges"

3. Ensure the "API Export" and "API Import/Update" boxes are ticked, and save

4. Click "API" in the left-hand menu column, then "Request an API token"

Your request requires approval by your REDCap administrator (you should receive an email confirmation when it is complete).

5. Return to your project's API page and you will see your token.

The API token below is ONLY for you and will work ONLY with this project. All activity performed using this token is logged as being performed by you! Treat this token like your username and password: it must NOT be shared with others.

If you think your token has been compromised, contact your REDCap administrator immediately AND either delete or regenerate your token.

REDCap provides the "API Playground" as an area where you can experiment with the different API methods and parameter options, It enables you to execute requests and view corresponding responses, and also generates boilerplate scripts in various different programming languages.

Have a play!

You will find that the interactions here are similar to what you do when using REDCap via your web browser: you send a request to the server, the server processes the request and returns an appropriate response. This is because the interaction is performed using the same mechanism: the HTTP protocol (with an encrypted connection, hence HTTPS).

Stata does not have inbuilt functionality for performing http requests (note you can load a .dta from an http url via webuse, but it does not work using https) but does offer the shell command, which enables you to pass data to other programms on your computer. We can use the popular command-line tool curl to perform the communication with the REDCap server.

Download a version of curl that is appropriate to your device and operating system: https://curl.haxx.se http:https://macappstore.org/curl/

It does not matter where on your system you copy the curl executable file (especially if you include the location in your PATH environment variable) but for the purposes of the following exercises it is assumed that you have the executable at: c:\curl\curl.exe

The following do-files are provided to illustrate different ways the REDCap API may be used, and different ways in which an appropriate do-file may be constructed.

1. Simple_Export.do

   • A basic API call to download all data from your REDCap project.

2. Export_Fields_Instruments.do

   • Specify specific fields and instruments to download.

3. Export_Filter.do

   • Specify an expression that will filter the records downloaded.

4. Export_Report.do

   • Specify a REDCap report to download.

5. Export_Metadata.do

   • Illustrating metadata (data dictionary) download - not just records.

6. Import_Records.do

   • Illustrating data import - API is not just for export.

7. Build_Command_String.do

   • An example of building the curl command programmatically.

8. Debugging.do

   • How to troubleshoot an API call that fails.

9. Delete_Records.do

   • An example of deleting multiple records.

10. Read_Token_From_File.do

    • An example of reading in your API token from an external (and private) file.

11. get_redcap_metadata.ado

    • An ado-file (program) for downloading data dictionary information and applying metadata to raw datasets.
    • Save to your ado directory and pass the API URL and token as arguments when you call it:
    • get_redcap_metadata "`apiurl'" "`apitoken'"

12. 12_File_Export_Import.do

    • Looping through records to export a file from one project and import it to the corresponding record in another.